Daniel Costinett
Office: | Min Kao 504 |
E-mail: |
ude.ktu@CJD |
Phone: | 865-974-3572 |
Fax: | 865-974-5483 |
Address: | Min H. Kao Building, Suite 504 1520 Middle Drive Knoxville, TN 37996-2250 |
Biography
Daniel Costinett is a Professor in the Department of Electrical Engineering and Computer Science at the University of Tennessee Knoxville. He received his Ph.D. degree in Electrical Engineering at the University of Colorado at Boulder in 2013. In 2012, he assisted with research and course development as an instructor at Utah State University. His research interests include resonant and soft switching power converter design, high efficiency wired and wireless power supplies, on-chip power conversion, medical devices, and electric vehicles.
Dr. Costinett was a recipient of the National Science Foundation CAREER Award in 2017, the 2022 Richard M. Bass Outstanding Young Power Electronics Engineer Award, the 2016 and 2020 IEEE PELS Transactions Second Place Prize Paper Award, and the 2015 IEEE IAS William M. Portnoy Award. He received the 2022 Moses E. and Mayme Brooks Distinguished Professor Award, 2015 ECE Faculty of the Year Award, 2020 Chancellor’s Award for Professional Promise in Research from UTK, and 2023 Gonzalez Family Outstanding Researcher Award. He currently serves as Associate Editor of IEEE Transactions on Power Electronics.
Ongoing Research Projects
Completed Research Projects
- Multi-load Multi-frequency Wireless Power Transfer
- Electrosurgical Power Supply with Harmonic Control and Component Integration
- Increasing Power Density of Inductors using Electropermanent Magnets
- RF Wireless Energy Harvesting
- GaN-based Single-stage Transmitter for Wireless Power Transfer
- Fabrication of Custom Printed 3D Air Core Inductors
- SiC-Based Reconfigurable DC-DC Converter Design for Electric Vehicles (EV) Charging and Powertrain Application.
- Automated Device Analysis and Converter Design
- Intelligent Comprehensive Design and Operation Paradigm for WBG-Based Converters
- Intelligent Gate Drive for Maximizing Performance and Enhancing Reliability of Wide Bandgap Semiconductors
- Ultra-light Highly Efficient MW-Class Cryogenically Cooled Inverter for All Future Electric Aircraft Applications
- Little Box Challenge Inverter
- WBG-based Power Module for EV Traction Drives
- DC Controller for Continuously Variable Series Reactors (CVSRs)
- Coil Design for Wireless EV Charging
- GaN-Based Active ZVS Rectifier for 6.78 MHz Wireless Power Transfer
- 7-Level Switched Capacitor Rectifier for WPT
- Development of Ultra-High Efficiency, High-Density 3kW Single-Phase AC-DC Converter
- A High Frequency Wireless Power Transfer System for Electric Vehicle Charging Using Multi-layer Non-uniform Self-resonant Coil at MHz
- Reducing Levelized Cost of Energy (LCOE) of Residential PV Inverters Through Dynamic Hardware Allocation
- GaN-based Frequency Synchronous Rectifier with On-board Control for 6.78MHz Wireless Power Transfer
- A Smart and Highly Compact Power Electronics Box to Provide Universal Charging Technologies (OBC, Wireless and DC Fast Charging) along with DCDC
Current Students
PhD
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Arka Basu arrow_drop_down
Research Interests
Wireless power; Electric vehicles
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Kody Froehle arrow_drop_down
Research Interests
Lightweight wireless power transfer for UAVs
Graduated Students
PhD
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Kamal Sabi arrow_drop_down
Status
Kamal graduated in December 2022 and is curently employed by Texas Instruments
PhD Dissertation
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Chongwen Zhao arrow_drop_down
Status
Chongwen obtained his PhD in December 2018 and is currently employed by Apple Inc.
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Ling Jiang arrow_drop_down
Status
Ling graduated in December 2018 and is currently employed at Analog Devices, Inc.
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Saeed Anwar arrow_drop_down
Status
Saeed graduated in May 2020 and is currently employed by Busek
PhD Dissertation
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Jie Li arrow_drop_down
Status
Jie graduated in January, 2022 and is currently working at Apple. His MS thesis was Wireless Power System Design for Maximum Efficiency
PhD Dissertation
Research Projects
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Jared Baxter arrow_drop_down
Status
Jared Graduated in Spring 2024 and is currently working at Texas Instruments
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Spencer Cochran arrow_drop_down
Status
Spencer graduated in August 2021 and is now working for Astranis. His MS thesis was A GaN-Based Synchronous Rectifier with Reduced Voltage Distortion for 6.78 MHz Wireless Power Applications
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Andrew Foote arrow_drop_down
Status
Andrew graduated in October 2023 and is currently employed by Volkswagen Group of America
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Jingjing Sun arrow_drop_down
Status
Jingjing graduated in March 2022 and is currently working at Analog Devices, Inc.
PhD Dissertation
Research Projects
- Development of Ultra-High Efficiency, High-Density 3kW Single-Phase AC-DC Converter
- A High Frequency Wireless Power Transfer System for Electric Vehicle Charging Using Multi-layer Non-uniform Self-resonant Coil at MHz
- Development of a Converter-Based Emulator for Data Center Power Distribution System
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Ruiyang Qin arrow_drop_down
Status
Ruiyang graduated in March 2022 and is currently working at Tesla
PhD Dissertation
Research Projects
- Coil Design for Wireless EV Charging
- A High Frequency Wireless Power Transfer System for Electric Vehicle Charging Using Multi-layer Non-uniform Self-resonant Coil at MHz
- A Smart and Highly Compact Power Electronics Box to Provide Universal Charging Technologies (OBC, Wireless and DC Fast Charging) along with DCDC
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Weimin Zhang arrow_drop_down
Status
Weimin graduated with his PhD in August 2015 and is now working at Apple, Inc.
MS
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Maeve Lawniczak arrow_drop_down
Status
Maeve graduated with her MS in Summer 2018, and is current employed at Schneider Electric
Research Projects
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Doug Bouler arrow_drop_down
Status
Doug graduated with his MS in Summer 2018 and is currently employed at Texas Instruments
Research Projects
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Gabriel Gabian arrow_drop_down
Status
Gabriel graduated in August 2017 and is currentl employed by Allegro MicroSystems, LLC
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Jordan Gamble arrow_drop_down
Status
Jordan graduated with his MS in Spring 2018 and is current employed at LTK Engineering Services
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Quillen Blalock arrow_drop_down
Status
Quillen Blalock graduated with an MS in electrical engineering in May 2020 and is employed at Texas Instruments in Knoxville, Tennessee.
Research Projects
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Peter Pham arrow_drop_down
Status
Peter graduated in July 2020 and is currently employed by Analog Devices
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Joseph Setelin arrow_drop_down
Status
Joey graduated in May 2022 and is currently working for Texas Instruments
BS
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Rafael Camarillo arrow_drop_down
Status
Rafael graduated in May 2018 and is currently employed by Booz Allen Hamilton
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Kyle Goodrick arrow_drop_down
Status
Kyle graduated in May 2017 and started the PhD program at The University of Colorado Boulder
Research Projects
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Jay Vahaly arrow_drop_down
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Yael Garcia arrow_drop_down
Publications
Journal Papers
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IEEE Transactions on Power Electronics2024
arrow_drop_downHigh-power inductive wireless power transfer (WPT) systems for EVs are designed to meet specifications such as stray field, power level, efficiency, misalignment tolerance, and ground clearance. These metrics are all heavily influenced by the coil geometry. This paper proposes a coil design method based on the Fourier Analysis Method (FAM) which is an analytical method for directly designing coil geometries to meet stray field and power level requirements through an optimization of Fourier basis function coefficients. In this work, two 120 kW WPT proof-of-concept demonstrators with low stray field and high efficiency are built from FAM optimization results to validate the models and show the impact of the FAM design process. Experimental validation of the Gen. 2 demonstrator at 120 kW output power resulted in a measured DC/DC efficiency of 97.2% at alignment with a 125 mm airgap. At the 120 kW test point, the stray fields 80 cm away from the center of the airgap between the coil assemblies were 3.4 µT(rms) on the X-axis and 3.5 µT(rms) on the Y-axis, much lower than the 27 µT(rms) ICNIRP limit.
[BibTeX]IEEE Transactions on Transportation Electrification2024
arrow_drop_downWith the growth of electric vehicle (EV) popularity, different charging options to increase user convenience and reduce charging times are being considered and researched. Among these, inductive wireless power transfer (WPT) systems for EVs are being designed to meet specifications such as stray field, power level, efficiency, misalignment tolerance, and ground clearance, which are all heavily influenced by the coil geometry. The proposed Fourier Analysis Method (FAM) is an analytical method to directly design coil geometries to meet stray field and power level requirements through an optimization of Fourier basis function coefficients. The outputs of the optimization are complex, planar coil geometries that meet the power level and stray field constraints with minimized loss factors. Contours of these potentials determine the coil conductor paths and loss models predict the system efficiency and performance over misalignment. The Fourier representation of the geometry is used to conveniently calculate the coupling over misalignment, external proximity effect loss, and ferrite loss. A 6.6 kW prototype WPT system with low stray field and high efficiency is built from the optimization results to validate the models and showcase the usefulness of the FAM design approach.
[BibTeX]IEEE Transactions on Industrial Electronics2024
arrow_drop_downTo further improve the system integration and convenience of the battery charging system for electric vehicles, this letter proposed a multipurpose magnetic coupler-based charging solution that integrates bidirectional on-board charger (OBC), wireless power transfer (WPT), and an auxiliary power module (APM). The proposed solution presents multiple highlights: 1) the first exhibited solution to integrate OBC, WPT, and APM in one unit; 2) magnetic integration that uses a multiwinding WPT pad to eliminate the main transformer of OBC and APM; and 3) topological integration that saves multiple active and passive devices. This letter includes a description of the system topology, operation principles of individual charging modes, a novel magnetic coupler, and the design methodology. Finally, a prototype was constructed and different charging modes were tested to validate the proposed design.
[BibTeX]IEEE Transactions on Power Electronics2023
arrow_drop_downThis paper provides a complete coil and shielding design solution for a 6.6 kW electric vehicle wireless power transfer system based on compact self-resonant (SR) coils. Due to the presence of a conductive vehicle body above the receiver coil, vertical fringing flux must be shielded in any electric vehicle wireless charger. Using high-frequency SR coils, parasitic capacitance introduced by standard shielding design approaches degrades the quality factor of the coils. In this work, the high-frequency parasitic capacitance introduced by the magnetic and conductive shielding materials is analyzed in detail, and a shielding geometry optimization method is proposed. Using ferrite and an additional dielectric spacer, prototype aluminum-backed SR coils are fabricated to validate the modeling. The total thicknesses of the transmitter and receiver coils are only 11.4 mm and 7.4 mm, respectively. The prototype coils achieve 92.3% DC-DC efficiency and 7.1 kW/dm3 volumetric power density. This paper demonstrates the first 6.6 kW WPT system for EV charging using compact megahertz-self-resonant coils including a complete magnetic and conductive shielding implementation.
[BibTeX]IEEE Transactions on Power Electronics2023
arrow_drop_downThis article proposes a high-efficiency single-phase GaN-based rectifier with reactive power transfer for use in front-end power supplies as an efficient alternative to centralized reactive power compensation. A full-range zero-voltage switching (ZVS) modulation for both unity power factor (PF) operation and nonunity PF operation is proposed for the GaN-based rectifier in critical conduction mode (CRM) operation. A frequency limitation method is also developed to limit the peak frequency during the ac current zero-crossing. Also, a GaN-based T-type totem-pole rectifier is proposed to overcome the control challenge in CRM during the ac voltage zero-crossing. Meanwhile, a digital-based control scheme is developed to implement ZVS operation and reactive power regulation. The proposed rectifier and ZVS control have the advantages of simple topology, high efficiency, straightforward control implementation, and capability of flexible reactive power regulation. A 1.6-kVA prototype of the GaN-based CRM T-type totem-pole rectifier is built and demonstrated with full-range ZVS operation, 98.9% full-load efficiency, and flexible reactive power regulation with smooth dynamic response.
[BibTeX]IEEE Transactions on Power Electronics2022
arrow_drop_downA high-power, high-frequency wireless power transfer system for electric vehicles (EVs) is proposed in this article with lightweight and compact coil design. Leveraging a multilayer nonuniform self-resonant coil, no external capacitor is needed for compensation and the high-frequency conduction loss is mitigated by sharing current between multiple copper layers. The analytical model for the proposed coil is provided, and prototype coils with 200-mm radius are fabricated and tested, achieving a quality factor over 450 at 3 MHz. The optimized design for both coils and a GaN-based power stage are detailed and validated experimentally. Experimental tests show 95.2% dc–dc efficiency with 6.6-kW power transferred across a 100-mm coil-to-coil distance with 52.5 kW/m2 power density. The system demonstrates the first 6.6-kW wireless power transfer system for EV charging using compact self-resonant coils at MHz.
[BibTeX]IEEE Transactions on Power Electronics2022
arrow_drop_downIn this article, a wireless charging architecture employing a multilevel switched-capacitor (MSC) ac–dc rectifier is investigated. The proposed MSC rectifier features a multilevel design that is scalable to accommodate different power ratings and load ranges. The topology showcases advantages for wireless power transfer (WPT) systems in terms of compactness, efficiency, impedance tunability, and harmonic attenuation. The single-stage active topology is capable of varying its low-distortion staircase input voltage to tune the WPT system for high system-wide efficiency. A seven-level, 20-W prototype is used to verify the WPT loading and loss analysis. The prototype operates at 150 kHz with up to 3:1 step-down conversion ratio to an output voltage of 5.0 V. The experimental peak dc-to-dc efficiency is 93.8% and the rectifier peak efficiency is 98.3%. The rectifier demonstrates low waveform distortion and high efficiency across many WPT loading conditions, solidifying its place as a strong candidate for wireless power applications.
[BibTeX]IEEE Transactions on Power Electronics2022
arrow_drop_downThis article details the systematic design of a 100-W multiload wireless charging station. The station provides positional flexibility for the receivers, exhibits limited cross-channel disturbance, and has high efficiency. The positional flexibility is achieved using a transmitter coil design approach, which uses interleaved windings and controlled coil geometry to shape the magnetic field. The limited cross-channel disturbance is realized with an immittance network, which maintains a constant transmitter coil current. A holistic system-level modeling and design method is proposed to design the entire system for maximum efficiency. The first step is decoupling each stages using parameterized source and/or load of adjacent stages, and optimize internally for minimum loss, which leads to a reduced design space. The second step is system-wide optimization, which addresses power loss interdependence. A 100-W, 6.78-MHz experimental system with a 0.5 × 0.5 m
transmitter coil is demonstrated. The measured magnetic field variation on the charging surface is 15.9%. And the system shows no cross-channel disturbance when charging two 50-W receivers. The measured dc-to-dc efficiency is 92.8%.$^2$ [BibTeX]IEEE Open Journal of Power Electronics2021
arrow_drop_downThe GaN-based critical conduction mode (CRM) totem-pole power factor correction (PFC) converter with full-line-cycle zero voltage switching (ZVS) is a promising candidate for high-efficiency front-end rectifiers. However, the input current can be degraded by line-cycle current distortion and ac line zero-crossing current spikes, and maintaining reliable ZVS control is difficult in noise-susceptible high-frequency environments. In this paper, a detailed analysis of the current distortion issues in a GaN-based CRM totem-pole PFC with digital ZVS control is provided, and effective approaches are proposed to mitigate different kinds of current distortion and ensure stable ZVS control under high-frequency operation. The proposed solutions have the advantages of straightforward implementation and do not increase the control complexity. The current distortion issues are demonstrated in two GaN-based CRM totem-pole PFC prototypes, a 1.5 kW PFC for data centers and a 100 W PFC in a 6.78 MHz wireless charging power supply for consumer electronics. The proposed methods are experimentally verified with effective mitigation of the current distortion and improvement of the converter power efficiency.
[BibTeX]IEEE Transactions on Power Electronics2020
arrow_drop_downThis article establishes an analytical model for the device drain-source overvoltage related to the two loops in three-level active neutral point clamped (3L-ANPC) converters. Taking into account the nonlinear device output capacitance, two common modulation methods are investigated in detail. The results show that the line switching frequency device usually has higher overvoltage, and the switching speed of the high switching frequency device is not strongly influenced by the multiple loops. By keeping the nonactive clamping switch off, the effect of the nonlinear device output capacitance can be significantly mitigated, which helps reduce the overvoltage. Moreover, the loop inductance can be reduced with vertical loop layout and magnetic cancellation in the printed circuit board and busbar design. A 500-kVA 3L-ANPC converter using silicon carbide mosfets was built and tested. The experimental results validate the overvoltage model of the two modulation methods as well as the busbar design. With the nonactive clamping switch off, the overvoltage of both the high and line switching frequency devices is significantly reduced, which helps achieve higher switching speed.
[BibTeX]IEEE Journal of Emerging and Selected Topics in Power Electronics2020
arrow_drop_downIn order to evaluate the feasibility of newly developed gallium nitride (GaN) devices in a cryogenically cooled converter, this article characterizes a 650-V enhancement-mode GaN high-electron mobility transistor (GaN HEMT) at cryogenic temperatures. The characterization includes both static and dynamic behaviors. The results show that this GaN HEMT is an excellent device candidate to be applied in cryogenic-cooled applications. For example, transconductance at cryogenic temperature (93 K) is 2.5 times higher than one at room temperature (298 K), and accordingly, peak di/dt during turn-on transients at cryogenic temperature is around 2 times of that at room temperature. Moreover, the ON-resistance of the channel at the cryogenic temperature is only one-fifth of that at room temperature. The corresponding explanations of performance trends at cryogenic temperatures are also given from the view of semiconductor physics. In addition, several device failures were observed during the dynamic characterization of GaN HEMTs at cryogenic temperatures. The ultrafast switching speed-induced high di/dt and dv/dt at cryogenic temperatures amplify the negative effects of parasitics inside the switching loop. Based on failure waveforms, two failure modes were classified, and detailed failure mechanisms caused by ultrafast switching speed are given in this article.
[BibTeX]IEEE Transactions on Power Electronics2020
arrow_drop_downTo better support the superconducting propulsion system in the future aircraft applications, the technologies of high-power high switching frequency power electronics systems at cryogenic temperatures should be investigated. This article presents the development of a 40-kW cryogenically cooled three-level active neutral point clamped inverter with 3 kHz output line frequency and 140 kHz switching frequency. Si mosfets are characterized at cryogenic temperatures, and the results show that they have promising performance such as lower on-resistance and switching loss. The design of the inverter is presented in detail with the special consideration of the cryogenic temperature operation. Moreover, a packaging and integration architecture is designed and fabricated to demonstrate the feasibility and performance of the inverter in the lab. It is able to achieve no leakage with good thermal and air insulation. With the inverter and packaging, the experimental results show that the inverter operates properly at cryogenic temperatures. The loss is measured at different load conditions, and the loss analysis is given, which shows that the cryogenically cooled inverter has 30% less loss than operating at room temperature.
[BibTeX]IEEE Transactions on Power Electronics2020
arrow_drop_downParalleling three phase three-level inverters is gaining popularity in industrial applications. However, analytical models for the harmonics calculation of a three-level neutral point clamped (NPC) inverter with popular space vector modulation (SVM) are not found in the literature. Moreover, how interleaving angle impacts the dc- and ac-side harmonics and electromagnetic interference (EMI) harmonics in parallel interleaved three-level inverters and how to optimize interleaving angle to reduce these harmonics have not been discussed in the literature. Furthering previous study, this article presents the modeling, analysis, and reduction of harmonics in paralleled and interleaved three-level NPC inverters with SVM. Analytical models for harmonic calculation are developed, and the dc-side harmonics characteristics of an NPC inverter are identified. The impact of interleaving angle on the ac-side voltage and dc-link current harmonics of parallel interleaved three-level NPC inverters is comprehensively studied. The impact of switching frequency and interleaving angle on EMI harmonics is also illustrated. Optimal interleaving angle ranges to reduce these harmonics are derived analytically. The developed models and harmonic reduction analysis are verified experimentally with two paralleled and interleaved three-level NPC inverters.
[BibTeX]IEEE Transactions on Power Electronics2020
arrow_drop_downThe attenuation performance of an electromagnetic interference filter can be significantly degraded by coupling, parasitics, and frequency-dependent nonlinearity, especially in high frequency (HF) range. This article reveals and investigates a mutual capacitive coupling effect in the popular filter structures with T-shaped joint. The mechanism is explained and the impact on filter attenuation is analyzed, which show this coupling is the dominant cause of performance degradation of T-shaped filters and a major cause for other T-shape-related filters. The effect patterns for both common-mode (CM) and differential-mode (DM) filters are analytically derived and further examined in multistage filter structures. Mitigation solutions using PCB slits and grounded shielding are proposed to improve filter transfer gain up to 30 dB in the HF range. A topological strategy is also presented, further enhancing filter attenuation. In addition, the impact of relative positions of the inductors on the coupling capacitance is discussed, and five positions are experimentally studied and compared. Experimental results obtained from three-phase LCL and LCLC filters verify the significance of this coupling and the effectiveness of the mitigation methods.
[BibTeX]IEEE Transactions on Power Electronics2020
arrow_drop_downIn order to apply power electronics systems to applications such as superconducting systems under cryogenic temperatures, it is necessary to investigate the characteristics of different parts in the power electronics system. This article reviews the influence of cryogenic temperature on power semiconductor devices including Si and wide bandgap switches, integrated circuits, passive components, interconnection and dielectric materials, and some typical cryogenic converter systems. Also, the basic theories and principles are given to explain the trends for different aspects of cryogenically cooled converters. Based on the review, Si active power devices, bulk Complementary metal-oxide-semiconductor (CMOS) based integrated circuits, nanocrystalline and amorphous magnetic cores, NP0 ceramic and film capacitors, thin/metal film and wirewound resistors are the components suitable for cryogenic operation. Pb-rich PbSn solder or In solder, classic printed circuit boards material, most insulation papers and epoxy encapsulant are good interconnection and dielectric parts for cryogenic temperatures.
[BibTeX]IEEE Transactions on Industrial Electronics2020
arrow_drop_downThis paper studies how an outer fractional winding can impact the equivalent parallel capacitance (EPC) of a differential-mode inductor, which is a critical passive component in a power electronic converter to combat with electromagnetic noises, and proposes a winding scheme that can reduce EPC and increase inductance, achieving both high-frequency filtering performance and high density. To perform these studies, a comprehensive layer capacitance model based on energy equivalence principle is established, which decouples EPC contribution among three elements, i.e., outer fraction layer, layer-to-layer, and layer-to-core, thus enabling the impact evaluation of different winding elements and schemes. Experimental comparison results have validated the accuracy of this EPC model and excellent performance of the proposed winding scheme with EPC reduction by 4×. It reveals that contrary to previous understanding, the inverse winding, in fact, is more effective for EPC reduction than the direct winding in most of the partial layer scenarios, and that by using this scheme with the outer fraction layer, 45% higher inductance and slightly less EPC can be achieved, compared to the single-layer winding design.
[BibTeX]IEEE Journal of Emerging and Selected Topics in Power Electronics2020
arrow_drop_downThree-level converters are more susceptible to parasitics compared with two-level converters because of their complicated structure with multiple switching loops. This paper presents the methodology of busbar layout design for three-level converters based on magnetic cancellation effect. The methodology can fit for 3L converters with symmetric and asymmetric configurations. A detailed design example is provided for a high power three-level active neutral point clamped (ANPC) converter, which includes the module selection, busbar layout, and DC-link capacitor placement. The loop inductance of the busbar is verified with simulation, impedance measurements, and converter experiments. The results match with each other, and the inductances of short and long loops are 6.5 nH and 17.5 nH respectively, which are significantly lower than the busbars of NPC type converters in other references.
[BibTeX]2020
arrow_drop_downSeries-series compensated inductive power transfer (SSIPT) systems have been widely studied and characterized for constant resistance loads (CRLs) and constant voltage loads (CVLs), but much less so for constant power loads (CPLs), although CPLs have numerous applications. In this work, we address some of the fundamental knowledge gaps for SSIPT/CPL systems that we believe have not been fully explored in the literature. First, we apply Middlebrook's stability criterion to derive a closed-form impedance-based stability condition for SSIPT/CPL systems. The derivation of the equilibrium solution is based on small-signal analysis and we show its consistency with intuitive results from perturbation-based arguments. Second, we show that the power transfer efficiency is minimum at the resonant frequency of the primary resonator. Third, the stability criterion is used to develop a straightforward approach for finding the operating frequency and input voltage that achieves near-maximum power transfer efficiency. This solution is useful as a starting point for a more meticulous parameter sweep to find the optimum input voltage and frequency values. Our analytical results are validated by performing frequency sweep measurements with two SSIPT experimental setups - one tuned to 165 kHz and the other to 6.78 MHz. We also provide an intuitive description and comparison of voltage-driven and current-driven CPLs. This topic is rarely treated in an intuitive manner and largely ignored, but we believe a solid conceptual understanding of voltage-driven and current-driven CPLs is beneficial for designers.
[BibTeX]IEEE Journal of Emerging and Selected Topics in Power Electronics2019
arrow_drop_downTo understand the limitation of maximizing the switching speed of SiC low current discrete devices and high current power modules in hard switching applications, double pulse tests are conducted and the testing results are analyzed. For power modules, the switching speed is generally limited by the parasitics rather than the gate drive capability. For discrete SiC devices, the conventional voltage source gate drive (VSG) is not sufficient to maximize the switching speed even if the external gate resistance is minimized. The limitation of existing current source gate drives (CSG) are analyzed, and a CSG dedicated for SiC discrete devices is proposed, which can provide constant current during the switching transient regardless of the high Miller voltage and large internal gate resistance. Compared with the conventional VSG, the proposed CSG achieves 67% faster turnon time and 50% turn-off time, and 68% reduction in switching loss at full load condition.
[BibTeX]IEEE Transactions on Power Electronics2019
arrow_drop_downThis paper identifies extra junction capacitances and switching commutation loops introduced by line-frequency devices (i.e., non-active every other half line cycle) in three-level ac/dc converters and investigates the corresponding effects. Junction capacitances and power loops are well known as the key factors that impact converter switching loss and device stress, thus influence device selection, power stage layout, and thermal design. By examining switching transients of the commonly used T-shaped and I-shaped three-level converters, the cause and mechanism of the extra junction capacitances and power loops are presented. The impacts on switching loss, device voltage stress, and ac-side voltage/current distortion are respectively reported and analyzed. A loss calculation scheme for the three-level converter to include that extra loss is proposed. A power layout scheme to mitigate the device voltage stress is provided. Compensation and modeling of the voltage and current distortion are also proposed. Experimental results conducted on several types of three-level converter prototypes including a gallium nitride based 115 Vac/650 Vdc/1.5-kW/450-kHz Vienna-type rectifier and a SiC MOSFET based 1-kV/10-kW/ 280-kHz three-level active neutral-point-clamped inverter confirm the presented effects and verify the associated analysis and solutions.
[BibTeX]IEEE Transactions on Power Electronics2019
arrow_drop_downA single-stage 6.78 MHz transmitter is proposed, which directly converts a utility ac input to a regulated, high-frequency (6.78 MHz) ac output for wireless power transmission. The topology integrates a totem-pole rectifier operating in a discontinuous conduction mode and an asymmetrical voltage cancellation controlled full-bridge inverter. Compared with the traditional cascaded multistage transmitters, this single-stage approach achieves high power efficiency over the full load range, utilizes fewer fast-switching devices, and shrinks the size of the converter. Constant current behavior at the output of the transmitter enables a fast response to a sudden load change. The operation and theoretical analysis of the single-stage transmitter is verified using a 100 W, GaN-based prototype. Experimental results demonstrate the capability of the converter to provide high power factor, low total harmonic distortion of the input current, and high conversion efficiency over the whole power range. The resulting prototype is suitable for implementation in wireless power systems where multiple consumer electronics loads are charged from a single transmitter.
[BibTeX]IEEE Transactions on Power Electronics2019
arrow_drop_downJunction temperature is an important design/operation parameter, as well as, a significant indicator of device's health condition for power electronics converters. Compared to its silicon (Si) counterparts, it is more critical for silicon carbide (SiC) devices due to the reliability concern introduced by the immaturity of new material and packaging. This paper proposes a practical implementation using an intelligent gate drive for online junction temperature monitoring of SiC devices based on turn-off delay time as the thermo-sensitive electrical parameter. First, the sensitivity of turn-off delay time on the junction temperature for fast switching SiC devices is analyzed. A gate impedance regulation assist circuit is proposed to enhance the sensitivity by a factor of 60 and approach 736 ps/°C tested in the case study with little penalty on the power conversion performance. Next, an online monitoring unit based on gate assist circuits is developed to monitor the turn-off delay time in real time with the resolution less than 104 ps. As a result, the micro-controller is capable of “reading” junction temperature during the converter operation. Finally, a SiC-based half-bridge inverter is constructed with an intelligent gate drive consisting of the gate impedance regulation circuit and online turn-off delay time monitoring unit. Experimental results demonstrate the feasibility and accuracy of the proposed approach.
[BibTeX]IEEE Transactions on Power Electronics2019
arrow_drop_downAs wide-bandgap (WBG) devices and applications move from niche to mainstream, a new generation of engineers trained in this area is critical to continue the development of the field. This paper introduces a new hands-on course in characterization of WBG devices, which is an emerging and fundamental topic in WBG-based techniques. First, the lecture-simulation-experiment format based course structure and design considerations, such as safety, are presented. Then, the necessary facilities to support this hands-on course are summarized, including classroom preparation, software tools, and laboratory equipment. Afterward, the detailed course implementation flow is presented to illustrate the approach of close interaction among lecture, simulation, and experiment to maximize students' learning outcomes. Finally, grading for students and course evaluation by students are discussed, highlighting the findings and potential improvements. Detailed course materials are provided via potenntial.eecs.utk.edu/WBGLab for educational use.
[BibTeX]CPSS Transactions on Power Electronics and Applications2018
arrow_drop_downA systematic study on a gallium nitride (GaN) high-electron-mobility transistor (HEMT) based battery charger, consisting of a Vienna-type rectifier plus a dc-dc converter, reveals a common phenomenon. That is, the high switching frequency, and high di/dt and dv/dt noise inside GaN converters may induce a dc drift or low frequency distortion on sensing signals. The distortion mechanisms for different types of sensing errors are identified and practical minimization techniques are developed. Experimental results on the charger system have validated these mechanisms and corresponding approaches, showing an overall reduction of input current total harmonic distortion (THD) by up to 5 percentage points and improved dc-dc output voltage regulation accuracy. The knowledge helps engineers tackle the troublesome issues related to noise.
[BibTeX]IEEE Transactions on Power Electronics2018
arrow_drop_downWide bandgap semiconductors are gradually being adopted in high power-density high efficiency applications, providing faster switching and lower loss, and at the same time imposing new challenges in control and hardware design. In this paper, a gallium nitride-based Vienna-type rectifier with SiC diodes is proposed to serve as the power factor correction stage in a high-density battery charger system targeting for aircraft applications with 800 Hz ac system and 600 V level dc link, where power quality is required according to DO160E standard. To meet the current harmonic requirement, PWM voltage distortion during the turn-off transient, is studied as the main harmonics contributor. The distortion mechanism caused by different junction capacitances of the switching devices is presented. A mitigation scheme considering the nonlinear voltage-dependent characteristics of these capacitances is proposed and then simplified from a pulse-based turn-off compensation method to a general modulation scheme. Simulation and experimental results with a 450 kHz Vienna-type rectifier demonstrate the performance of the proposed approach, showing a THD reduction from 10% to 3% with a relatively low-speed controller.
[BibTeX]IEEE Transactions on Power Electronics2017
arrow_drop_downNewly emerged gallium nitride (GaN) devices feature ultrafast switching speed and low on-state resistance that potentially provide significant improvements for power converters. This paper investigates the benefits of GaN devices in an LLC resonant converter and quantitatively evaluates GaN devices' capabilities to improve converter efficiency. First, the relationship of device and converter design parameters to the device loss is established based on an analytical model of LLC resonant converter operating at the resonance. Due to the low effective output capacitance of GaN devices, the GaN-based design demonstrates about 50% device loss reduction compared with the Si-based design. Second, a new perspective on the extra transformer winding loss due to the asymmetrical primary-side and secondary-side current is proposed. The device and design parameters are tied to the winding loss based on the winding loss model in the finite element analysis (FEA) simulation. Compared with the Si-based design, the winding loss is reduced by 18% in the GaN-based design. Finally, in order to verify the GaN device benefits experimentally, 400- to 12-V, 300-W, 1-MHz GaN-based and Si-based LLC resonant converter prototypes are built and tested. One percent efficiency improvement, which is 24.8% loss reduction, is achieved in the GaN-based converter.
[BibTeX]IEEE Transactions on Power Electronics2017
arrow_drop_downThis paper presents an intelligent gate drive for silicon carbide (SiC) devices to fully utilize their potential of high switching-speed capability in a phase-leg configuration. Based on the SiC device's intrinsic properties, a gate assist circuit consisting of two auxiliary transistors with two diodes is introduced to actively control gate voltages and gate loop impedances of both devices in a phase-leg configuration during different switching transients. Compared to conventional gate drives, the proposed circuit has the capability of accelerating the switching speed of the phase-leg power devices and suppressing the crosstalk to below device limits. Based on Wolfspeed 1200-V SiC MOSFETs, the test results demonstrate the effectiveness of this intelligent gate drive under varying operating conditions. More importantly, the proposed intelligent gate assist circuitry is embedded into a gate drive integrated circuit, offering a simple, compact, and reliable solution for end-users to maximize benefits of SiC devices in actual power electronics applications.
[BibTeX]IEEE Transactions on Power Electronics2017
arrow_drop_downWith the increased cloud computing and digital information storage, the energy requirement of data centers keeps increasing. A high-voltage point of load (HV POL) with an input series output parallel structure is proposed to convert 400 to 1 VDC within a single stage to increase the power conversion efficiency. The symmetrical controlled half-bridge current doubler is selected as the converter topology in the HV POL. A load-dependent soft-switching method has been proposed with an auxiliary circuit that includes inductor, diode, and MOSFETs so that the hard-switching issue of typical symmetrical controlled half-bridge converters is resolved. The operation principles of the proposed soft-switching half-bridge current doubler have been analyzed in detail. Then, the necessity of adjusting the timing with the loading in the proposed method is analyzed based on losses, and a controller is designed to realize the load-dependent operation. A lossless RCD current sensing method is used to sense the output inductor current value in the proposed load-dependent operation. Experimental efficiency of a hardware prototype is provided to show that the proposed method can increase the converter's efficiency in both heavy- and light-load conditions.
[BibTeX]IEEE Transactions on Power Electronics2017
arrow_drop_downDead time significantly affects the reliability, power quality, and efficiency of voltage-source converters. For silicon carbide (SiC) devices, considering the high sensitivity of turn-off time to the operating conditions (> 5× difference between light load and full load) and characteristics of inductive loads (> 2× difference between motor load and inductor), as well as large additional energy loss induced by the freewheeling diode conduction during the superfluous dead time (~15% of the switching loss), then the traditional fixed dead time setting becomes inappropriate. This paper introduces an approach to adaptively regulate the dead time considering the current operating condition and load characteristics via synthesizing online monitored turn-off switching parameters in the microcontroller with an embedded preset optimization model. Based on a buck converter built with 1200-V SiC MOSFETs, the experimental results show that the proposed method is able to ensure reliability and reduce power loss by 12% at full load and 18.2% at light load (8% of the full load in this case study).
[BibTeX]IEEE Transactions on Industrial Electronics2017
arrow_drop_downMultifrequency wireless power transfer (WPT) is advantageous in facilitating compatibility with different WPT standards. However, implementing a multifrequency transmitter often requires compromises in system size, complexity, power transfer capability, or output regulation. In this paper, a single-inverter-based dual-mode WPT system is proposed. The system employs a multifrequency programmed pulse width modulation scheme. This multifrequency modulated inverter can simultaneously generate and regulate 100-kHz and 6.78-MHz outputs, or multiple frequencies within ranges of 87-300 kHz, which facilitates the development of multistandard WPT technology for consumer electronics. The principle of the proposed modulation is illustrated, where two different frequencies are concurrently modulated using a programmed pulse train of square waveforms for power delivery, while eliminating certain harmonics. Design tradeoffs and constraints are examined through analytical circuit models. Finally, experimental results are provided to verify the method on a gallium-nitride-based WPT prototype.
[BibTeX]IEEE Transactions on Power Electronics2016
arrow_drop_downElectric-drive vehicles, including hybrid, plug-in hybrid, and electric vehicles, require a high-voltage (HV) battery pack for propulsion and a low-voltage (LV) dc bus for auxiliary loads. This paper presents an architecture that uses modular dc-dc bypass converters to perform active battery cell balancing and to supply current to auxiliary loads, eliminating the need for a separate HV-to-LV high step-down dc-dc converter. The modular architecture, which achieves continuous balancing of all cells, can be used with an arbitrary number of cells in series, requires no control communication between converters, and naturally shares the auxiliary load current according to the relative state-of-charge (SOC) and capacities of the battery cells. Design and control details are provided for LV low-power dual active bridge (DAB) power converters serving as the bypass converter modules. Furthermore, current sharing is examined and worst-case SOC and current deviations are derived for mismatches in cell capacities, SOCs, and parasitic resistances. Experimental results are presented for a system consisting of 21 series 25 Ah Panasonic lithium-ion NMC battery cells and 21 DAB bypass converters, with combined outputs rated to supply a 650-W auxiliary load.
[BibTeX]IEEE Transactions on Power Electronics2016
arrow_drop_downThis paper presents a comprehensive short-circuit ruggedness evaluation and numerical investigation of up-to-date commercial silicon carbide (SiC) MOSFETs. The short-circuit capability of three types of commercial 1200-V SiC MOSFETs is tested under various conditions, with case temperatures from 25 to 200 °C and dc bus voltages from 400 to 750 V. It is found that the commercial SiC MOSFETs can withstand short-circuit current for only several microseconds with a dc bus voltage of 750 V and case temperature of 200 °C. The experimental short-circuit behaviors are compared, and analyzed through numerical thermal dynamic simulation. Specifically, an electrothermal model is built to estimate the device internal temperature distribution, considering the temperature-dependent thermal properties of SiC material. Based on the temperature information, a leakage current model is derived to calculate the main leakage current components (i.e., thermal, diffusion, and avalanche generation currents). Numerical results show that the short-circuit failure mechanisms of SiC MOSFETs can be thermal generation current induced thermal runaway or high-temperature-related gate oxide damage.
[BibTeX]IEEE Journal of Emerging and Selected Topics in Power Electronics2016
arrow_drop_downGallium nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This paper reviews the characteristics and commercial status of both vertical and lateral GaN power devices, providing the background necessary to understand the significance of these recent developments. In addition, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic Rds,on, breakdown mechanisms, thermal design, device availability, and reliability qualification. This review will help prepare the reader to effectively design GaN-based converters, as these devices become increasingly available on a commercial scale.
[BibTeX]IEEE Journal of Emerging and Selected Topics in Power Electronics2016
arrow_drop_downGallium nitride (GaN) heterojunction field-effect transistors are an enabling technology for high-density converter design. This paper proposes a three-level dc-dc converter with dual outputs based on enhancement-mode GaN devices, intended for use as a battery charger in aircraft applications. The charger can output either 28 or 270 V, selected with a jumper, to satisfy the two most common dc bus voltage requirements in airplanes. It operates as an LLC converter in the 28 V mode and as a buck converter in the 270 V mode. In both operation modes, the devices can realize zero voltage switching (ZVS). With the chosen modulation method, the converter can realize automatic voltage balancing of the flying capacitor and the frequency doubling function to act as an interleaved converter. For the LLC mode, the resonant frequency is twice the switching frequency of primary-side switches, and for the buck mode, the frequency of the output inductor current is also twice the switching frequency. This helps to reduce the size of magnetics while maintaining a low switching loss. Also, the converter utilizes a matrix transformer, with resonant parameters designed to reduce conduction loss and avoid ZVS failure. The operating principle of the converter is analyzed and then experimentally verified on a 1.5-kW prototype with 1 MHz resonant frequency.
[BibTeX]IEEE Journal of Emerging and Selected Topics in Power Electronics2016
arrow_drop_downHigh power density is a desirable feature of power electronics design, which prompts economic incentives for industrial applications. In this paper, a gallium nitride (GaN)-based 2-kVA single-phase inverter design was developed for the Google Little Box Challenge, which achieves a 102-W/in3 power density. First, the static and dynamic temperature-dependent characteristics of multiple SiC and enhancement-mode GaN FETs are investigated and compared. Based on the device testing results, several topologies of the inverter stage and different power decoupling solutions are compared with respect to the device volume, efficiency, and thermal requirements. Moreover, some design approaches for magnetic devices and the implementation of gate drives for GaN devices are discussed in this paper, which enable a compact and robust system. Finally, a dc notch filter and a hard switching full-bridge converter are combined as the proposed design for the prototype. A 2-kVA prototype is demonstrated, which meets the volume, efficiency, and thermal requirements. The performance of the prototype is verified by the experimental results.
[BibTeX]IEEE Transactions on Power Electronics2015
arrow_drop_downNonlinear, voltage-dependent capacitances of power semiconductor devices are capable of having significant impact on the operation of switched-mode power converters. Particularly at high switching frequency, these nonlinearities play a significant role in determining switching times, losses, and converter dynamics during switching transitions. In order to accommodate the well-established design and analysis techniques commonly used for linear circuits, this paper examines the nonlinear voltage-dependence of switching device capacitances and proposes a circuit-oriented analysis technique that allows the parasitic capacitances to be replaced with linear equivalents. The multitude of developed equivalents are verified through full nonlinear simulation in both MATLAB/Simulink and SPICE, as well as through experimental results.
[BibTeX]IEEE Transactions on Power Electronics2015
arrow_drop_downDouble pulse test (DPT) is a widely accepted method to evaluate the switching characteristics of semiconductor switches, including SiC devices. However, the observed switching performance of SiC devices in a PWM inverter for induction motor drives is almost always worse than the DPT characterization, with slower switching speed, more switching losses, and more serious parasitic ringing. This paper systematically investigates the factors that limit the SiC switching performance from both the motor side and inverter side, including the load characteristics of induction motor and power cable, two more phase legs for the three-phase PWM inverter in comparison with the DPT, and the parasitic capacitive coupling effect between power devices and heat sink. Based on a three-phase PWM inverter with 1200 V SiC MOSFETs, test results show that the induction motor, especially with a relatively long power cable, will significantly impact the switching performance, leading to a switching time increase by a factor of 2, switching loss increase up to 30% in comparison with that yielded from DPT, and serious parasitic ringing with 1.5 μs duration, which is more than 50 times of the corresponding switching time. In addition, the interactions among the three phase legs cannot be ignored unless the decoupling capacitors are mounted close to each phase leg to support the dc bus voltage during switching transients. Also, the coupling capacitance due to the heat sink equivalently increases the junction capacitance of power devices; however, its influence on the switching behavior in the motor drives is small considering the relatively large capacitance of the motor load.
[BibTeX]IEEE Transactions on Power Electronics2015
arrow_drop_downThis paper presents a board-level integrated silicon carbide (SiC) mosfet power module for high temperature and high power density application. Specifically, a silicon-on-insulator (SOI)-based gate driver capable of operating at 200 °C ambient temperature is designed and fabricated. The sourcing and sinking current capability of the gate driver are tested under various ambient temperatures. Also, a 1200 V/100 A SiC mosfet phase-leg power module is developed utilizing high temperature packaging technologies. The static characteristics, switching performance, and short-circuit behavior of the fabricated power module are fully evaluated at different temperatures. Moreover, a buck converter prototype composed of the SOI gate driver and SiC power module is built for high temperature continuous operation. The converter is operated at different switching frequencies up to 100 kHz, with its junction temperature monitored by a thermosensitive electrical parameter and compared with thermal simulation results. The experimental results from the continuous operation demonstrate the high temperature capability of the power module at a junction temperature greater than 225 °C.
[BibTeX]IEEE Transactions on Power Electronics2013
arrow_drop_downThis letter describes a very simple implementation of a digital pulse width modulator (DPWM) under 100 ps resolution in low-cost field-programmable gate arrays (FPGAs). The implementation is based on internal carry chains and logic resources which are present in most FPGA families. The proposed approach does not require manual routing or placement, consumes few hardware resources, and does not rely heavily on specialized phase-locked loop or clock management resources. A 50-MHz switching frequency DPWM with 60-ps resolution and a 1-MHz switching frequency DPWM with 90-ps resolution are experimentally demonstrated, with monotonicity and excellent linearity.
[BibTeX]IEEE Transactions on Power Electronics2013
arrow_drop_downA control scheme is developed to maximize efficiency over a wide range of loads for a dual active bridge converter. A simple control circuit using only phase-shift modulation is proposed which considers both the converter conversion ratio and switching dead times in order to maintain high efficiency in the presence of varying loads. To demonstrate feasibility of the proposed control method, experimental results are presented for a 150-to-12 V, 120-W, 1-MHz prototype converter which has 97.4% peak efficiency and maintains greater than 90% efficiency over a load range between 20 and 120 W.
[BibTeX]Proceedings of the IEEE2013
arrow_drop_downThis paper discusses far-field wireless powering for low-power wireless sensors, with applications to sensing in environments where it is difficult or impossible to change batteries and where the exact position of the sensors might not be known. With expected radio-frequency (RF) power densities in the 20-200- μW/cm2 range, and desired small sensor overall size, low-power nondirective wireless powering is appropriate for sensors that transmit data at low duty cycles. The sensor platform is powered through an antenna which receives incident electromagnetic waves in the gigahertz frequency range, couples the energy to a rectifier circuit which charges a storage device (e.g., thin-film battery) through an efficient power management circuit, and the entire platform, including sensors and a low-power wireless transmitter, and is controlled through a low-power microcontroller. For low incident power density levels, codesign of the RF powering and the power management circuits is required for optimal performance. Results for hybrid and monolithic implementations of the power management circuitry are presented with integrated antenna rectifiers operating in the 1.96-GHz cellular and in 2.4-GHz industrial-scientific-medical (ISM) bands.
[BibTeX]IEEE Transactions on Circuits and Systems II: Express Briefs2011
arrow_drop_downThis brief discusses a low-power wireless sensor based on commercial components for sensing and data transmission. The sensor is wirelessly powered from the far field through an integrated single or dual-polarization antenna, rectifier, and power management module. Since the unit is intended for mobile use, the variable available power is monitored, and the duty cycle for wireless data transmission adaptively adjusted through the use of a low-power microcontroller and a custom power management circuit. In sleep mode, the circuit consumes 1 μA at 2.5 V.
[BibTeX]Journal of Physics A: Mathematical and Theoretical2009
arrow_drop_downQuantum engineering of electronic energy states using nanoscale layers of semiconductor compounds allows the design and the observation of quantum phenomena which are typically observed in atomic structures. Furthermore, semiconductors are present in nearly all modern electronic devices and are a crucial component of integrated circuits. Due to the relatively high rate of manufacturing defects, it is crucial to have a method for testing new semiconductor formations without requiring a sample to be fabricated. A simple, fast and very accurate numerical technique is presented to calculate the eigenstates of such arbitrary quantum structures. The method is based on a high-order finite difference scheme which allows the use of sparse matrix algebra, thus, significantly reducing computational time and allowing for high precision results even for the high energy states.
[BibTeX]Conference Papers
TitleYear-
2024 IEEE Applied Power Electronics Conference and Exposition (APEC)2024
arrow_drop_downNonlinear magnetic properties in power electronics applications, such as permeability and core loss cause significant discrepancies between magnetic designs and prototype measurements, leading to iterative prototyping efforts. To address this issue, a bottom-up approach that is based on the physics of magnetic material is proposed to unveil the fundamental origin of nonlinearity. The physical parameters such as magnetization, gyromagnetic ratio, damping factor, etc., are translated to equivalent circuit parameters. The nonlinear magnetization dynamics of a single magnetic domain are described by an equivalent circuit model derived from the Landau-Lifshitz-Gilbert (LLG) equation. A fictitious magnetic domain is used to demonstrate the developed model’s capability on predicting the nonlinearity that includes magnetization dynamics and hysteresis. Then, the model is further validated by a commercial material, TDK N87 toroidal core. The results such as B-H loop and permeability simulated from the circuit model are in close agreement with the datasheet, validating the feasibility of predicting magnetic material’s nonlinear performance from physics perspective rather than empirical approaches.
[BibTeX]2023 IEEE 24th Workshop on Control and Modeling for Power Electronics (COMPEL)2023
arrow_drop_downBroad-scale modeling and optimization play a vital role in the design of advanced power converters. Optimization is normally implemented via brute force iterations of design variables or utilizing metaheuristic techniques which are time consuming for a wide range of potential topologies, device implementations, and operating points. Recently, discrete time state-space modeling has shown merits in rapid analysis and generality to arbitrary circuit topologies but has not yet been utilized under rapid optimization techniques across multiple converter parameters. In this work, we investigate methods to incorporate rapid gradient-based optimization techniques to leverage discrete time state-space modeling and showcase the approach in the power converter design process. The method is validated on a 48-to-1V converter designed using the proposed techniques.
[BibTeX]2023 IEEE Applied Power Electronics Conference and Exposition (APEC)2023
arrow_drop_downThis paper details a fully compensated self-resonant coil (FSRC) with series LC resonance and reduced surface electric field for application in wireless power transfer for consumer electronics. By having a repeated series LC connection along the entire coil trace, the proposed series resonant structure achieves high-Q, low E-field, and thin profile simultaneously. The impact of ferrite shielding is also studied. Different E-field compensation coil geometries are studied, and a systematic design method is presented for optimal coil performance. Experimental tests verify the coil function, modeling, and design.
[BibTeX]Design and Optimization of a High Gravimetric Power Density Receiver for Wireless Charging of Drones2023 IEEE 24th Workshop on Control and Modeling for Power Electronics (COMPEL)2023
arrow_drop_downThis article presents the weight optimization of a receiver for wireless drone charging applications. There is need for comprehensive modeling to minimize the onboard weight on the flying drone platform. A systematic approach that codesigns all stages of the wireless charger, based on comprehensive loss, weight, and thermal modeling, is put forward to minimize the onboard weight for drone wireless charging applications. A 200 W, GaN-based prototype is implemented to validate the modeling. The prototype has been tested up to 204 W without any active cooling. The receiver achieves a gravimetric power density of 8.3 W/g excluding the weight of connectors, sensing, and control. Index Terms-Wireless power transfer (WPT), power density, synchronous rectifier.
[BibTeX]2023 IEEE Energy Conversion Congress and Exposition (ECCE)2023
arrow_drop_downIntegrated chargers have gained an increasing interest in the electric vehicle (EV) industry. Existing solutions such as the integrated onboard charger (OBC) and auxiliary power module (APM) save the cost and the size, however, it only provides limited functions and hard to be integrated with the future wireless power transfer (WPT) technology. This paper proposed a multi-function magnetic coupler-based integrated charger that provides bidirectional OBC, WPT charging, and APM functions in a single system. In addition to the multi-port converter topology, a multi-winding WPT charging pad is repurposed serving as the main transformer in the OBC and APM modes as well. The paper briefs the system topology, explains various charging modes, and details the magnetic coupler design. Furthermore, a prototype was constructed and successfully delivered 6.6kW in OBC mode, 3.3kW in V2L mode, 6.6kW in WPT mode, and 800W in APM mode, which validates the proposed design.
[BibTeX]2023 IEEE Energy Conversion Congress and Exposition (ECCE)2023
arrow_drop_downThis paper, to the best knowledge of the authors, for the first time reports the packaging of a 100kW three-level active neutral point clamped (3L-ANPC) phase leg power module for electric vehicle (EV) traction inverter applications using 650V/150A e-mode gallium nitride high-electron-mobility transistors (GaN HEMTs). Compared with two-level (2L) half bridge power module, the main challenges of packaging a 3L-ANPC phase leg power module are high number of switches (6 switches vs 2 switches) and multiple commutation loops (1 commutation loop vs 4 commutation loops). In addition, there are four switches involved in the two long commutation loops. Those parasitic loop inductances must be minimized simultaneously. Those challenges are addressed by meticulous packaging of the power module, featuring low power loop inductances, double-sided cooled power module, low junction-to-coolant thermal resistance, symmetrical layout for the two parallel dies of each switch and mechanical robustness, etc. The simulated loop inductances are 1.92nH for the short loops and 5.21nH for the long loops, respectively; resulting in a 471V and 540V of turn-off voltage spikes in a double pulse test simulation at 400V/200A. The simulated junction-to-coolant thermal resistances are 0.37°C/W and 0.53°C/W for different switches, respectively.
[BibTeX]2023 IEEE Energy Conversion Congress and Exposition (ECCE)2023
arrow_drop_downTo build an integrated battery charger with multiple functions for electric vehicles (EVs), the system normally has several stages, such as AC/DC power factor conversion (PFC) converter, isolated and/or non-isolated DC/DC converters. Therefore, it is important to implement the start-up and shutdown procedure by coordinating multi-stage converters to avoid potential large inrush current or over voltage. This paper firstly proposed a highly integrated multi-stage battery charger for electric vehicles that offers multiple functions, including on-board charger (OBC), vehicle-to-load (V2L), wireless power transfer (WPT), all using a 400V battery, and auxiliary power module (APM) for a 12V battery. The control methods for each function are introduced. Based on the system configuration and characteristics of different functions, comprehensive system-level start-up and shut-down schemes are proposed for practical operation scenarios of OBC, WPT and V2L. Finally, a 400VAC/800VDC/22kW prototype is built and the effectiveness of the proposed start-up and shut-down schemes is verified by experiments.
[BibTeX]2023 IEEE Energy Conversion Congress and Exposition (ECCE)2023
arrow_drop_downAs inductive wireless charging reaches higher power levels, thermal management and mechanical durability become more critical. To address these concerns, past works have demonstrated the benefit of encapsulating coil assemblies in thermally conductive materials. However, due to the sensitivity of the MnZn ferrites commonly used in coil assemblies to mechanical stress, care must be taken to avoid creating large stresses in the ferrite that cause higher hysteresis loss. The stress formation in the encapsulant curing process is overviewed and modeled and an experiment is performed to demonstrate the effect in a small-scale coil assembly. Finally, the effect is shown in the reduced coil-coil efficiency of a first generation high power inductive power transfer prototype using a stiff epoxy compared to better performance in a second prototype using a softer thermally-conductive silicone encapsulant.
[BibTeX]2022 IEEE Energy Conversion Congress and Exposition (ECCE)2022
arrow_drop_downThis paper proposes a high-efficiency single-phase GaN-based T-type totem-pole front-end rectifier with reactive power transfer. A full-range zero voltage switching (ZVS) modulation approach for both unity power factor (PF) operation and non-unity PF operation is proposed for the GaN-based rectifier in critical conduction mode (CRM) operation. T-type mode operation and switching frequency limitation are proposed to overcome the ac-line zero-crossing challenges. A digital-based control strategy is also proposed to regulate the active power and reactive power simultaneously. A 1.6 kVA prototype of the T-type totem-pole rectifier is built and demonstrated with full-range ZVS operation, 98.9% full-load efficiency, and flexible reactive power regulation.
[BibTeX]2022 IEEE Design Methodologies Conference (DMC)2022
arrow_drop_downSchematic-level optimization and steady-state loss modeling play a vital role in the design of advanced power converters. Recently, discrete time state-space modeling has shown merits in rapid analysis and generality to arbitrary circuit topologies but has not yet been utilized under rapid optimization techniques. In this work, we investigate methods for the incorporation of rapid gradient-based optimization techniques leveraging discrete time state-space modeling and showcase the utility of the approach for use in the converter design process.
[BibTeX]2021 IEEE Applied Power Electronics Conference and Exposition (APEC)2021
arrow_drop_downAn investigation of a resonant reactive shielding coil for wireless power transfer (WPT) systems is presented in this work. The shielding coil attenuates the magnetic field above and to the side of air-core WPT coils. A parameterized coil model is used to allow arbitrary circular winding geometry and current direction. Detailed modeling and mathematical calculations are provided, and an optimized design algorithm is proposed. The design method is validated using an experimental prototype shielding coil applied to a 3.03 MHz electric vehicle (EV) WPT system operating at 500 W output power. Experimental results show that the peak flux density on the top-center area of the coil is suppressed from 105 μT to 50 μT, and the magnetic field to the side of the vehicle is maintained well below the safety standard. In addition, effect of the shielding coil in WPT systems with metal and ferrite plates is investigated.
[BibTeX]2021 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)2021
arrow_drop_downActive rectifiers enhance WPT systems via tunability, high efficiency, and low waveform distortion. However, utilizing these benefits requires that two circuit characteristics are managed simultaneously: the switching frequency must be synchronized to the transmitter and the output must be regulated. Furthermore, the fundamental benefit of impedance tunability inherent to the active rectifier necessitates that this dual-objective control problem remains stable over a wide range of operating points. Either control loop can be designed in isolation, and under this premise, this work contributes a closed form derivation for the cross-coupling behaviors in the control architecture for a 7-level switched capacitor WPT system. Finally, regions of attenuated cross-coupling effects are identified and used to experimentally demonstrate wide-range control with stable output regulation and frequency synchronization.
[BibTeX]2021 IEEE Energy Conversion Congress and Exposition (ECCE)2021
arrow_drop_downPower electronic inverters for photovoltaic (PV) systems over the years have trended towards high efficiency and power density. However, reliability improvements of inverters have received less attention. Inverters are one of the lifetime-limiting elements in most PV systems. Their failures increase system operation and maintenance costs, contributing to an increased lifetime energy cost of the PV system. Opportunities exist to increase inverter reliability through design for reliability techniques and the use of new modular topologies, semiconductor devices, and energy buffering schemes. This paper presents the implementation and design for reliability for a GaN-based single-phase residential string inverter using a new topological and control scheme that allows dynamic hardware allocation (DHA). In the proposed inverter architecture, a range of identical modules and control schemes are used to dispatch hardware resources within the inverter to variably deliver power to the load or filter the second harmonic current on the DC side. This new approach more than triples the lifetime of GaN-based inverters, reducing system repair/replacement costs, and increasing the PV system lifetime energy production.
[BibTeX]2020 IEEE Applied Power Electronics Conference and Exposition (APEC)2020
arrow_drop_downIn paralleled three-phase three-level voltage source inverters, sometimes the currents of paralleled inverters need to be separately adjusted to control power sharing, and the reference vectors will differ in phase and amplitude. In other cases, although the current references of the paralleled inverters are set to be the same, the d-axis and q-axis current closed-loop control outputs of each converter cannot be exactly the same due to the asymmetry in hardware or software. As a result, the reference vector of each inverter may also be different in terms of phase and amplitude. When conventional three-level space vector pulse width modulation (SVPWM) is applied, periodical jump can be observed in the phase current of each inverter and the zero sequence circulating current (ZSCC). This paper investigates the current jump phenomenon in paralleled three-level inverters with space vector modulation (SVM). The mechanism that causes the current jump is illustrated. A modulation method to eliminate this current jump is proposed. Simulation and experimental results are presented to verify the effectiveness of the proposed method and conducted analysis.
[BibTeX]Modeling and Analysis of Zero Common-mode Voltage Modulation with Dead-Time for Three-Level Inverter2020 IEEE Applied Power Electronics Conference and Exposition (APEC)2020
arrow_drop_downThis paper presents the modeling and analysis of zero common-mode voltage (ZCMV) pulse width modulation with dead-time for three-level voltage source inverters. Analytical model to calculate phase output voltage harmonic of three-level inverter with ZCMV modulation is developed. With ZCMV modulation, the common-mode voltage (CMV) of a three-level inverter can be eliminated in theory. However, CMV reduction performance is limited by dead-time in practical applications. Hence, the harmonic characteristics of CMV is modeled and analyzed considering dead-time. Experiments are conducted on a three-level neutral point clamped inverter with ZCMV modulation, and verify the accuracy of developed models.
[BibTeX]2020 IEEE Energy Conversion Congress and Exposition (ECCE)2020
arrow_drop_downThis paper presents the design of a transmitter coil with an interleaved structure for multi-load wireless power transfer (WPT) applications covering a large charging area. The proposed coil achieves receiver positional flexibility, low electric field generation, and high efficiency. Analytical modeling of the coil magnetic field distribution, electric field generation, and power loss is presented and utilized in the coil design process. A prototype 0.5 m x 0.5 m transmitter coil is built and tested in a 6.78 MHz WPT system. The magnetic field is uniform across the entire charging are with less than 8% variation in amplitude. The overall system efficiency is 92.8% when loaded with two 50 W diode rectifiers.
[BibTeX]2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)2020
arrow_drop_downSteady-state modeling plays an important role in the design of advanced power converters. Typically, steady-state modeling is completed by time-stepping simulators, which may be slow to converge to steady-state, or by dedicated analysis, which is time-consuming to develop across multiple topologies. Discrete time state-space modeling is a uniform approach to rapidly simulate arbitrary power converter designs. However, the approach requires modification to capture state-dependent switching, such as diode switching or current programmed modulation. This work provides a framework to identify and correct state-dependent switching within discrete time state-space modeling and shows the utility of the proposed method within the power converter design process.
[BibTeX]2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)2020
arrow_drop_downWireless power transfer (WPT) systems for Electric Vehicles (EVs) are designed to meet specifications such as stray field, power transfer, efficiency, and ground clearance. Typical design approaches include iterative analysis of predetermined coil geometries to identify candidates that meet these constraints. This work instead directly generates WPT coil shapes and magnetic fields to meet specifications and constraints through the optimization of Fourier basis function coefficients. The proposed Fourier Analysis Method (FAM) applies to arbitrary planar coil geometries and does not rely on iterative finite-element analysis (FEA) simulations. This flexibility allows for rapid design evaluation across a larger range of coil geometries and design specifications. A prototype coil is built to compare FAM outputs to experimental measurements and FEA simulations. The FAM is then used to illustrate the tradeoff of coil current and stray field for a given power level showing that the method is capable of generating optimized coil shapes to meet arbitrary field constraints.
[BibTeX]2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)2020
arrow_drop_downIn wireless power transfer (WPT) applications, the multi-level switched capacitor topology achieves significant advantages in terms of efficiency, system loading, THD, and output regulation. The topology requires dual-loop control in order to harness these benefits. First, a small signal discrete time model for the 7-level rectifier WPT system is developed. Then, a control loop is designed that enables the rectifier to regulate DC load voltage by varying its modulation scheme. Next, the WPT carrier frequency is sensed and a phase-locked loop is used in combination with the small signal power stage model to design a closed-loop controller that synchronizes frequency and regulates control phase through adjustments of the switching period. Finally, cross-coupling interactions between the two control loops are modeled, and stable dual-loop operation is shown.
[BibTeX]2020 IEEE Energy Conversion Congress and Exposition (ECCE)2020
arrow_drop_downIn this paper, an automated controller for an integrated, reconfigurable dc-dc converter for plugin electric vehicles (EVs) is presented. The integrated converter combines both an interleaved boost converter and dual active bridge (DAB) converter, sharing magnetics and switching devices. The converter switches between operating modes using the existing battery management system (BMS) contactors. The integrated converter operates in isolated DAB mode during battery charging operation. During traction operation, the integrated converter is operated in interleaved boost mode for heavy load and DAB mode during light load, high voltage operation. An online transition algorithm is used to transition from interleaved boost mode to DAB mode with minimal bus distortion. The automated controller selects the operating mode and inverter bus voltage at different torque-speed conditions to get maximum overall traction drive efficiency. An experimental prototype of the integrated converter demonstrates the automated controller functionality.
[BibTeX]2020 IEEE Energy Conversion Congress and Exposition (ECCE)2020
arrow_drop_downIn wireless power transfer systems, active rectifiers demonstrate improved efficiency and regulation capability. To enable impedance or output regulation, ensure stable operation, and maximize the efficiency, switching actions of the rectifier have to be synchronized with the magnetic field generated from the transmitter coil. This work presents an implementation of a phase- locked-loop synchronization controller using commercial components, including a low-cost microcontroller. A discrete-time small-signal model is used to derive the transfer function of the inherent feedback and design a compensator stabilizing the synchronization loop. Large-signal state-space modeling is used to design a high-efficiency, soft-switching, 6.78MHz power stage. A low-profile, 40W, GaN-based rectifier prototype is designed and built to experimentally verify the ability to synchronize and achieve high efficiency due to soft-switching.
[BibTeX]2020 IEEE Energy Conversion Congress and Exposition (ECCE)2020
arrow_drop_downA high power, high frequency wireless power transfer system for EV applications is proposed in this paper with lightweight and compact coil design. Leveraging a multi-layer non-uniform self-resonant coil, no external capacitor is needed for compensation and the high frequency conduction loss is mitigated by sharing current between multiple copper layers. Prototype coils with 200 mm radius are fabricated and tested, achieving quality factor over 450 at 3 MHz. The optimized design for both coils and a GaN-based power stage are detailed and validated experimentally. Experimental tests show 93.2% dc-dc efficiency with 2.4kW transferred across a 100 mm air gap.
[BibTeX]2020 IEEE Energy Conversion Congress and Exposition (ECCE)2020
arrow_drop_downThe soft-switching gallium-nitride (GaN) based critical conduction mode (CRM) totem-pole power factor correction (PFC) converter is a good candidate for the front-end rectifier in wireless power transfer (WPT) applications. In multi-receiver MHz WPT systems, the PFC converter is required to have fast dynamic response and noise immunity. In this work, a GaN-based CRM totem-pole PFC converter is designed for a multi-receiver wireless charging power supply. Digital-based variable on-time control is used to achieve the zero voltage switching (ZVS) within the whole line cycle, and a voltage-loop controller with notch filters is designed to improve the transient response. The impact of high-frequency noise on the sensing signals and ZVS control are analyzed, and implementation methods are proposed to mitigate the disturbances. A GaN-based CRM totem-pole PFC that is demonstrated with 98.5% full-load efficiency is built as the first stage in the transmitter of a 100 W 6.78 MHz multi-receiver WPT system. The noise immunity of the CRM PFC is verified by testing the whole WPT system. Experimental results show that the system end-to-end efficiency at full load is 90.16%, and fast dynamic response is achieved during load variation.
[BibTeX]2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL)2019
arrow_drop_downModeling plays a vital role in the design of advanced power converters. Commonly, modeling is completed using either dedicated hand analysis, which must be completed individually for each topology, or time-stepping circuit simulations, which are insufficiently rapid for broad analysis considering a wide range of potential designs or operating points. Discrete time state-space modeling of switching converters has shown merits in rapid analysis and generality to arbitrary circuit topologies but is hampered by difficulty incorporating nonlinear elements. In this work, we investigate methods for the incorporation of nonlinear elements into a generalized discrete time state-space modeling framework and showcase the utility of the approach for use in the converter design process.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downZero voltage switching (ZVS) has been widely implemented to improve the efficiency and robustness of high switching frequency converters. However, once the converter loses ZVS, the abrupt increase in switching loss decreases efficiency and may damage the converter. In this paper, a voltage slope-based detection method is proposed to detect ZVS status and prevent the converter from continuously hard switching. This detection circuit converts the voltage slope of the switching node to a dc voltage, which is compared with a reference voltage for the ZVS criterion. When hard switching occurs, two actions can be chosen: either shutting down the converter or adjusting the dead time to regain ZVS. The detection is achieved with simple circuitry and little control effort. A 6.78 MHz inverter for WPT application is used to verify this detection method. Experimental results show that ZVS status is detected effectively.
[BibTeX]2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL)2019
arrow_drop_downActive rectifiers in wireless power transfer systems exhibit many benefits compared to diode rectifiers, including increased efficiency, controllable impedance, and regulation capability. To achieve these benefits, the receivers must synchronize their switching frequency to the transmitter to avoid sub-fundamental beat frequency oscillations. Without additional communication, the receiver must synchronize to locally-sensed signals, such as voltages and currents induced in the power stage by the transmitter. However, the waveforms in the receiver are dependent on both the transmitter and receiver operation, resulting in an internal feedback between sensing and synchronization which prohibits the use of traditional phase-locked-loop design techniques. In this digest, a discrete time state space model is developed and used to derive a small signal model of these interactions for the purpose of designing stable closed-loop synchronization control. A prototype 150 kHz wireless power transfer converter is used to experimentally validate the modeling, showcasing stable synchronization.
[BibTeX]2019 IEEE Energy Conversion Congress and Exposition (ECCE)2019
arrow_drop_downA multi-layer non-uniform self-resonant coil is proposed in this paper for wireless power transfer applications. Multiple layers of spiral coils are stacked up, and the capacitance between them is controlled by a dielectric material between the copper layers. The coil current is shared among all layers, and the current sharing ratio is determined by the variable-width spiral tracks. Compared with a two-layer self-resonant coil, current sharing across the multi-layer structure reduces total copper loss. The analytical model for the proposed coil is provided and used to optimize the design of the coil. Both finite-element simulation and prototype testing of a three-layer design are used to validate the model. The results confirm the predicted high quality factor series resonant behavior.
[BibTeX]2019 IEEE 7th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)2019
arrow_drop_downData center energy usage is expected to grow in the coming years with the proliferation of cloud services on daily life. The increasing energy demands that data centers will place upon the power grid necessitate the development high efficiency, high power density power supplies. The LLC resonant converter has long been utilized for data center power supplies as the dc-dc transformer to step down the voltage rectified from the ac transmission system to the rack level. As more is demanded of the data center and more information must be processed, space becomes more valuable. The use of wide bandgap materials such as Gallium Nitride (GaN) allows for much faster switching which can lead to higher power density by reducing the size of passive components. However, a higher frequency can lead to much greater switching loss. Zero-voltage switching (ZVS) can be utilized in primary side devices to greatly reduce losses. The achievement of ZVS is dependent on the magnetic design of the LLC transformer. By considering the effects of device capacitance and transformer parasitic capacitance and inductance, ZVS can be achieved to negate the turn-on losses and ensure high efficiency. This paper details the analysis of ZVS for a GaN-based LLC resonant converter with two series-parallel connected transformers.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downIn this paper, a variable frequency soft-switching control for a three-level half bridge (TLHB) buck converter is proposed to achieve wide-range output battery charging function without losing zero voltage switching (ZVS) or high efficiency. The adopted variable frequency triangle-current-modulation (TCM) is based on dc measurement and average-model calculation, thus able to realize ZVS operation fully digitally without current zero-crossing-detection (ZCD) circuits. A top-level average current or output voltage feedback controller further ensures the desired power or output voltage regulation. Experimental results from a GaN based TLHB prototype have shown the reliable TCM control and smooth transition of ZVS operation through the charging procedure.
[BibTeX]2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL)2019
arrow_drop_downAn analytical model for the device drain-source turn-on overvoltage in three-level active neutral point clamped (3L-ANPC) converters is established in this paper. Considering the two commutation loops in the converter, the relationship between the turn-on overvoltage and the loop inductances is evaluated. The line switching frequency device usually exhibits higher overvoltage, while the high switching frequency device is not strongly influenced by the multiple loops. A 500 kVA 3L-ANPC converter using SiC MOSFETs is tested, and the model is verified with the experimental results.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downIn order to enable wireless charging of mobile electronics to compete with wired alternatives, wireless receivers need to operate at power levels sufficient to accommodate fast-charging standards. The receiver efficiency, harmonic content and total volume are key design metrics for wireless receivers. In this paper, four candidate topologies are compared, under 20 W fast-changing conditions, with respect to power loss, harmonic distortion, and power density. Each of the metrics are analyzed and verified experimentally. In coordination with the transmitter, a system-level approach to minimizing distortion is presented. Finally, the multilevel switched-capacitor rectifier is demonstrated to be a good candidate for wireless fast charging of mobile devices with high efficiency, small size, and suitable structure for future integration.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downIn paralleled voltage source inverters (VSI), circulating current has both high frequency and low frequency components, and its spectrum highly depends on the modulation scheme. Previous research has mostly focused on the circulating current suppression for paralleled two-level VSIs. Little literature exists on similar analysis for paralleled three-level VSIs using space vector modulation. A detailed circulating current spectrum on full frequency range has not been well developed. This paper presents an improved analytical model for three-level space vector modulation (SVM), considering the impacts of regularly sampled reference and dead time. Then, circulating harmonic currents are determined across the full frequency range for various interleaving angles of two three-level ANPC inverters. The calculated harmonics are also verified by experimental results.
[BibTeX]2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL)2019
arrow_drop_downControl based modulation techniques such as Boundary Current Mode (BCM) modulation are used to achieve zero voltage switching (ZVS) and overcome the increased switching losses in power electronics operating at high frequency. A simple control approach to implementing BCM uses dual current programmed mode (DCPM) control, but this approach is highly susceptible to noise and propagation delays at high switching frequency. Propagation delays in the control network cause the inductor current to overshoot its reference by a margin which varies with the instantaneous inductor current slope. This overshoot results in increased losses and introduces low-frequency inductor current distortion, particularly in high switching frequency converters. This work addresses propagation delay challenges by tuning the current sensing circuitry to mitigate impact of sensing delay, resulting in an inherent cancellation of sensing delay without additional control complexity. This approach is simple to implement and offers a flexible current control design for BCM modulation. The operation of this proposed compensation technique is demonstrated experimentally in a GaN-based full bridge inverter.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downWith conventional voltage source gate drives (VSG), the switching speed of SiC MOSFETs is difficult to increase due to large internal gate resistance, high Miller voltage, and limited gate voltage rating. This paper analyzes the requirement of current source gate drive (CSG) for SiC MOSFETs and proposes a CSG that can improve the switching speed and reduce switching loss. With the introduction of bi-directional switches, the influence of the large internal gate resistance of the SiC MOSFET can be mitigated, and sufficient gate current can be guaranteed throughout the switching transient. Therefore, the switching time and loss is reduced. The CSG can be controlled to be a VSG during steady state so the current of the gate drive is discontinuous and the stored energy of the inductor can be returned to the power supply to reduce gate drive loss. Double pulse tests are conducted for a SiC MOSFET with both conventional VSG and the proposed CSG. Testing results show that the switching loss of the proposed CSG is less than one third of the conventional VSG at full load condition.
[BibTeX]2019 AIAA/IEEE Electric Aircraft Technologies Symposium (EATS)2019
arrow_drop_downHigh power inverters will be a key enabler for future aircraft based on hybrid electric or turbo-electric propulsion as envisioned by NASA and Boeing. Cooling a power electronics converter to low temperature, e.g. using cryogenic cooling, can significantly improve the efficiency and power density of a power conversion system. This paper presents the design of a MW cryogenically-cooled power inverter for electric aircraft applications. The power semiconductor and magnetic component characterization, inverter topology and power stage design, modulation and control, EMI noise reduction and filters design, and cooling system design are illustrated. A MW-level inverter prototype has been assembled and tested. The experimental results verify the functionality of the inverter.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downParalleling power electronics inverters is an effective way to increase dc-ac system power level. Accurately synchronized switching action and independent closed-loop regulator are necessary to prevent circulating current in paralleled inverters. There are many challenges for the controller design, when the number of paralleled inverters is large, and control period gets short for high switching frequency applications. This paper presents a single controller design based on DSP + FPGA that is suitable for paralleling multiple inverters. A simple synchronization scheme between DSP and FPGA based on universal parallel port (UPP) is proposed to eliminate the synchronization delay among inverters, and independent control of each converter can also be implemented. The controller is built for a system consisting of 4 paralleled three-level, three-phase high frequency ANPC inverters using space vector modulation, and it can be easily adopted to other topologies and modulations. Experimental results have demonstrated the effectiveness of this controller.
[BibTeX]2019 IEEE Energy Conversion Congress and Exposition (ECCE)2019
arrow_drop_downThe adoption of SiC devices in high power applications enables higher switching speed, which requires lower circuit parasitic inductance to reduce the voltage overshoot. This paper presents the design of a busbar for a 500 kVA three-level active neutral point clamped (ANPC) converter. The layout of the busbar is discussed in detail based on the analysis of the multiple commutation loops, magnetic canceling effect, and DC-link capacitor placement. The loop inductance of the busbar is verified with simulation, impedance measurements, and converter experiments. The results match with each other, and the inductances of small and large loop are 6.5 nH and 17.5 nH respectively, which is significantly lower than the busbars of NPC type converters in other references.
[BibTeX]2019 IEEE Energy Conversion Congress and Exposition (ECCE)2019
arrow_drop_downHigh-frequency soft-switched gallium-nitride (GaN) based critical conduction mode (CRM) totem-pole power factor correction (PFC) converter is one of the most potential candidates in data center power supplies. However, the high-speed cycle-by-cycle zero current detection (ZCD) brings challenges to zero-voltage-switching (ZVS) control. Current sensing delay (CSD) exists, and the ZCD circuit is sensitive to high di/dt switching noise. In this paper, mechanisms of the ZCD time error are elaborated, and impacts of the current sensing delay on converter switching frequency, inductor current, input current third harmonic distortion (THD), and power loss are analyzed. Qualification time is added within the controller for immunity to the swiching noise, and a CSD embedded converter model is proposed to compensate the ZCD time delay. Also, loss modeling of the CRM totem-pole PFC is conducted to aid in analysis of the proposed theory. A 1.5 kW single-phase CRM totem-pole PFC prototype is tested. Experimental results validiate the analysis, modeling, and the proposed compensation method for current sensing delay.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downThe four-leg topology has been applied to two-level inverters for common-mode (CM) noise elimination. To achieve zero common-mode voltage (CMV), the zero vector typically used in the two-level inverter is not allowed. As a result, the reference cannot be synthesized by nearest three vectors, which introduces a penalty in dc voltage utilization and current THD. This paper applies the fourth-leg to three-level neutral point clamped (NPC) inverter fed motor drives. Unlike the case in the two-level inverter, the reference can be synthesized by the nearest three vectors while zero CMV can be achieved at the same time in a three-level inverter with the fourth-leg. The topology and modulation are presented. The fourth-leg filter structures are investigated, and a fourth-leg filter structure which decouples the fourth-leg from the main circuit power level is proposed for high power applications. The experiment results on a three-level NPC inverter show that with the fourth-leg and presented modulation applied, the CM noise has been significantly reduced, and around 25 dB attenuation can be observed at the first noise peak in the electromagnetic interference (EMI) frequency range.
[BibTeX]2019 IEEE Energy Conversion Congress and Exposition (ECCE)2019
arrow_drop_downThis paper presents the design and implementation of a boundary current mode (BCM) modulated GaN-based single phase inverter using a combination of bipolar and unipolar switching. Both unipolar and bipolar BCM-switched full bridge inverters are explored in detail in the context of efficiency, output current distortion and leakage current. Although the unipolar switched BCM inverter results in a higher efficiency in comparison to the bipolar switched inverter, it leads to a higher output current distortion at the low frequency zero crossing. On the other hand, the bipolar switched BCM inverter yields a low leakage current and reduced output current distortion, but exhibits lower efficiency. To overcome the low frequency zero crossing current distortion while maintaining a high efficiency, a combination of bipolar and unipolar switching in a BCM inverter is proposed. An experimental prototype has been built to validate the proposed control technique and modulation scheme. The proposed approach achieves a 2% efficiency improvement in comparison to the standard bipolar switched BCM inverter and a THD of 1.15%.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downThis paper details the inductor design and zero-voltage-switching (ZVS) control of a single-phase GaN-based critical-conduction-mode (CRM) totem-pole rectifier with power factor correction (PFC). A full-line-cycle ZVS strategy is derived, and an analytical converter model with ZVS margin is proposed. The boost inductor design is critical for the operation performance of the CRM totem-pole PFC. Based on analytical loss models, the inductor is designed and implemented using a toroidal powder core and litz wire to minimize converter loss and inductor size. Digital on-time control with real-time calculation and zero current detection (ZCD) is used to implement CRM. A 1.5 kW single-phase GaN-based CRM totem-pole PFC prototype is built and tested. With the on-time control, both the inductor current and the output voltage are well regulated. ZVS is realized for the whole line cycle, and the tested efficiency is 98.8% at full load.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downThis paper presents a comprehensive analytical analysis of the ac and dc side harmonics of the three-level active neutral point clamped (ANPC) inverter with space vector modulation (SVM) scheme. An analytical model to calculate the harmonics of a three-level converter with SVM is developed. The ac side output voltage harmonics and dc side current harmonics characteristics are calculated and analyzed. With the developed models, the impact of interleaving on both sides harmonics are studied which considers the modulation index, interleaving angle, and power factor. The analysis provides guideline for interleaving angle optimization to reduce the ac side power filter and dc side dc-link capacitor. The relationship between electromagnetic interference (EMI) filter corner frequency and switching frequency is also analytically derived which provides guideline for switching frequency and EMI filter design optimization. Two paralleled three-level ANPC inverters are constructed and experimental results are presented to verify the analytical analysis.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downWith the development of wide band-gap (WBG) technology, the switching speed of power semiconductor devices increases, which makes circuits more sensitive to parasitics. For three-level active neutral point clamped (3L-ANPC) converters, the over-voltage caused by additional non-active switch loop can be an issue. This paper analyzes the multiple commutation loops in 3L-ANPC converter and summarizes the impact factors of the device over-voltage. The nonlinearity of the output capacitance of the device can significantly influence the over-voltage. A simple control without introducing additional hardware circuit or complex software algorithm is proposed to attenuate the effect of the nonlinear output capacitance. Multi-pulse test is conducted for a 3L-ANPC converter built with silicon carbide (SiC) MOSFETs. With the proposed control, the testing results show that the peak drain-source voltage of both active and non-active switches is reduced by more than 20% compared to the conventional control.
[BibTeX]2019 IEEE Applied Power Electronics Conference and Exposition (APEC)2019
arrow_drop_downThis paper presents the coupled inductor design for interleaved three-level active neutral point clamped (ANPC) inverter considering electromagnetic interference (EMI) noise reduction. Compared to two-level case, the scenarios involved in the three-level space vector modulation (SVM) are more complicated when analyzing the volt-seconds of the coupled inductor for paralleled three-level inverter. At system level, the purpose of converter interleaving is to reduce EMI noise and ripple current in most applications, and coupled inductor design should consider the needs of EMI noise reduction and EMI filter design. These issues are discussed in this paper. The relationship between circulating current and EMI noise is illustrated. EMI filter corner frequency as a function of interleaving angle is analytically derived, and optimal interleaving angle for maximum common-mode (CM) filter and differential-mode (DM) filter corner frequencies is discussed. Coupled inductor design methodology for interleaved three-level inverters with SVM is then presented. Experiments on two interleaved ANPC inverters are conducted. The results verify the coupled inductor design. With the derived optimal interleaving angle, the CM and DM EMI noise are significantly reduced.
[BibTeX]2019 IEEE Energy Conversion Congress and Exposition (ECCE)2019
arrow_drop_downThis paper presents harmonic analysis of common-mode reduction (CMR) modulation for three-level voltage source inverters. The analytical model to calculate the harmonics of CMR modulation with arbitrary PWM sequence is developed. The impact of alternative PWM sequences of CMR modulation on harmonics is investigated. New three-state and four-state PWM sequences of CMR are proposed which spread the energy centered in the carrier frequency in the conventional CMR, and thus reduce the voltage peaks in frequency domain. Experiments are conducted on a three-level neutral point clamped inverter. Experiment results verify the developed analytical model and harmonic analysis.
[BibTeX]2018 AIAA/IEEE Electric Aircraft Technologies Symposium (EATS)2018
arrow_drop_downWide bandgap (WBG) semiconductor devices and cryogenic cooling are key enablers for highly-efficient ultra-dense power electronics converters, which are critical for future more electric aircraft applications. For the development and optimization of a cryogenically-cooled converter, an understanding of power semiconductor characteristics, especially for emerging WBG devices, is critical. This paper focuses on WBG device characterization at cryogenic temperatures. First, the testing setup for cryogenic temperature characterization is introduced. Then several WBG device candidates (e.g., 1200-V SiC MOSFETs and 650-V GaN HEMTs) are characterized from room to cryogenic temperatures. The test results are presented with trends summarized and analyzed, including on-state resistance, breakdown voltage, and switching performance.
[BibTeX]2018 IEEE Transportation Electrification Conference and Expo (ITEC)2018
arrow_drop_downAutomated vehicles require sensors and computer processing that can perceive the surrounding environment and make real time decisions. These additional electrical loads expand the auxiliary load profile, therefore reducing the range of an automated electric vehicle compared to a standard electric vehicle. Furthermore, a fully automated vehicle must be fail-safe from sensor to vehicle control, thus demanding additional electrical loads due to redundancies in hardware throughout the vehicle. This paper presents a review of the sensors needed to make a vehicle automated, the power required for these additional auxiliary loads, and the necessary electrical architectures for increasing levels of robustness.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downA planar coil structure that exhibits a series self-resonant behavior is developed for wireless power transfer systems which use magnetic resonant coupling. The proposed structure uses two thin, planar, spiral tracks separated by one layer of dielectric. By connecting to alternate ends of each track, the coil shows a series LC impedance, which is often necessary for voltage source inverters. An analytical model for the inductance, capacitance and resistance is used to develop a geometric design method that minimizes resistance given a set of application constraints. Experimental coils made with an FR4 PCB and an Teflon-ceramic PCB verify the proposed structure and modeling.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downSwitching transient overvoltage is inevitable in hard switching applications, and the faster switching speed of SiC MOSFETs suggests even worse overvoltage. This paper focuses on the turn-on overvoltage. To understand its nature, the switching transient is analyzed, and it shows the turn-on overvoltage is largely independent of load current condition. This phenomenon is verified by characterizing the turn-on overvoltage of a SiC MOFET and a SiC Schottky diode. Finally, a SPICE-based model is also built to understand the switching transient more accurately, and the modeling method can accurately predict the turn-on overvoltage and help select device voltage rating.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downIn this work, a hybrid switched-capacitor/PWM converter is analyzed and designed for battery charging in mobile electronics. Operation of the converter is reviewed to construct a complete analytical loss model based on FET extracted parameters for an integrated circuit implementation. The model is validated with experimental results and compared with other converter topologies in the same application. The loss modeling is used to optimize the physical scaling of the power transistors to minimize total losses.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downDead-time, device output capacitance, and other non-ideal characteristics cause voltage error for the midpoint PWM voltage of the semiconductor phase-leg employed in a voltage-source inverter (VSI). Voltage-second balancing is a well-known concept to mitigate this distortion and improve converter power quality. This paper proposes a unique voltage-second balancing scheme for a SiC based voltage source inverter using online condition monitoring of turn-off delay time and drain-source voltage rise/fall time. This data is sent to the micro-controller to be used in an algorithm to actively adjust the duty cycle of the input PWM gate signals to match the voltage-second of the non-ideal output voltage with an ideal output voltage-second. The monitoring system also allows for this implementation to eliminate the need for precise current sensing and allows for the implementation to be load independent. Dynamic current sensing is still a developing technology, and each load has a unique effect on the output voltage distortion. Test results for a 1 kW half-bridge inverter implementing this monitoring system and voltage-second balancing scheme show a 70% enhancement on the error against the ideal fundamental current value of the output current and a 2% THD improvement on the output current low frequency harmonics.
[BibTeX]2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)2018
arrow_drop_downThis work examines the application of GaN within Class D audio by providing a side-by-side comparison of enhancement-mode GaN devices with currently available silicon MOSFETs with 60 V drain-to-source voltage ratings. GaN in Class D audio will allow for lower heat radiation, smaller circuit footprints, and longer battery life as compared to Si MOSFETs with a negligible trade-off for quality of sound.
[BibTeX]2018 1st Workshop on Wide Bandgap Power Devices and Applications in Asia (WiPDA Asia)2018
arrow_drop_downIn this paper, an extra junction capacitance and its associated switching commutation path are identified in three-level ac/dc converters, which were previously overlooked due to the off-state of the related device in half line cycle. The impact of this effect on power loss is analyzed, showing an underestimated switching loss in the traditional loss calculation of three-level converters. Through a proposed loss re-evaluation approach based on energy data of conventional double pulse tester (DPT), the corrected loss matches experimental results obtained from a 450kHz 650 V Gallium Nitride (GaN) based Vienna-type rectifier, showing 17.4% additional switching loss due to this effect. And the dominant extra switching loss is found to be Coss loss instead of overlap loss in WBG converters. Thefore, the effect is severe in high swtiching frequency high-speed wideband gap (WBG) based three-level converters.
[BibTeX]2018 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow)2018
arrow_drop_downA single-stage transmitter is reviewed which directly converts a utility ac input to high frequency (6.78 MHz) ac output for wireless power transfer applications. Compared with a two-stage transmitter implementation, this single-stage transmitter obtains high power efficiency with reduced component-count. In this paper, a method is proposed to enable constant current at the output of the single-stage transmitter to accommodate multiple receivers. First, the constant output voltage transmitter is obtained by implementing closed-loop control and a model-based modulation scheme. Then, an impedance matching network is implemented at the output of transmitter to convert the constant voltage to constant current. This feature allows a single transmitter to charge multiple receivers simultaneously. The control methodology is verified using both simulation and a laboratory prototype.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downAs wide bandgap (WBG) semiconductors are gradually adopted for high switching frequency high power-density power converter, new challenges arise from control to hardware design. In this paper, an improved input current sampling method is proposed for three-phase rectifiers to avoid sampling noises when rectifiers are operated at high speed and high switching frequency. Experimental results obtained from a 450-kHz enhancement-mode Gallium Nitride (GaN) high-electron-mobility transistor (HEMT) based three-phase three-level Vienna-type rectifier demonstrate the good performance of the sampling method.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downData centers consume an ever-increasing amount of electricity because of the rapid growth of cloud computing and digital information storage. A high voltage point of load (HV POL) converter is proposed to convert the 400-VDC distribution voltage to 1-VDC within a single stage to increase the power conversion efficiency. A six-phase input series output parallel (ISOP) connected structure is implemented for the HV POL. The symmetrical controlled half bridge current doubler is selected as the converter topology in the ISOP structure. The full load efficiency is improved by 4% points compared with state of the art products. A voltage compensator has been designed in order to meet the strict dynamic voltage regulation requirement. A laboratory prototype has been built, and experimental results have been provided to verify the proposed HV POL with a single power conversion stage can meet the dynamic voltage regulation requirement for an on-board power supply with higher efficiency compared to the conventional architecture.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downA single-stage transmitter is reviewed, which directly converts a utility ac input to high frequency (6.78 MHz) ac output for wireless power transmission. By integrating two stages (totem-pole PFC rectifier and full bridge inverter) into a single stage, the topology achieves high efficiency and reduced component count. In this paper, a simple auxiliary circuit is added to allow the single-stage transmitter to operate in two modes. At heavy load, the transmitter operates as a totem-pole rectifier with PFC and achieves low distortion of the input current. At light load, the circuit operates as a voltage-doubler rectifier (VDR), extending the ZVS range of the transmitter. As a result, hard switching is avoided and efficiency is improved at light load. This improved single-stage transmitter is verified by a 100 W, GaN-based laboratory prototype.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downThe call for higher power and larger spatial freedom has driven the operating frequency of wireless power transfer (WPT) systems into the MHz range. Previous system design methods focus on designing the coils to attain high quality factor while remaining resonant around the working frequency and subsequently designing switching circuit hardware and operating point to minimize the system power loss. This sequential design method over-simplifies the system, neglecting inter-dependencies between system components, which leads to suboptimal designs. This paper presents a system design method that co-optimizes coils, power stages, and circuit operation for maximum overall efficiency, based on accurate models of converters and WPT system. The system model and the importance of co-design are verified by a 6.78 MHz WPT prototype.
[BibTeX]2018 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow)2018
arrow_drop_downIn mobile electronics applications, the high conduction loss on the ac-dc rectifier and the coil is a barrier to the application of wireless charging. In this paper, a wireless charging architecture employing a 7-level switched-capacitor (SC) ac-dc rectifier is investigated, showing a substantial reduction of the conduction losses on the transmitter, the coil and the receiver. The proposed SC rectifier also features a multilevel design with good scalability to accommodate different power ratings, and potentially reduce the harmonic contents of the input voltage. The principle and operation are verified using a 7-level, 20 W, 5-9 Vdc output, 150 kHz prototype. The measured peak dc-to-load system efficiency is above 90%. The high-power density design without bulky magnetic components is suitable for the implementation in low-profile mobile electronics.
[BibTeX]2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL)2018
arrow_drop_downResonant magnetic wireless power transfer (WPT) has potential to improve spatial freedom, allow simultaneous charging of multiple devices, and increase circuit power density. However, many obstacles must first be overcome before the benefits of this technology are fully realized. Due to the high frequency of the WPT carrier, autonomous receiver-side synchronization and control presents significant difficulties. This work addresses the control strategy of a 6.78 MHz GaN-based synchronous WPT rectifier. A zero-crossing current sensing scheme is used to both synchronize the receiver switching frequency and to enable control of its input phase. The rectifier is shown to be capable of regulating its output voltage by changing its input phase, highlighting the value of a circuit that has real-time control over the reactive part of its input impedance. The current sensing, frequency synchronization, and input phase control capabilities of the circuit are demonstrated experimentally and discussed in detail.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downAlthough SiC MOSFETs show superior switching performance compared to Si IGBTs, it is unknown whether SiC MOSFETs have the same advantage over Si super junction (SJ) MOSFETs such as CoolMOS. This paper analyzes the switching performance in different switching cell configurations and summarizes the impact factors that influence switching loss. A double pulse test is conducted for a SiC MOSFET and a CoolMOS with the same voltage and current rating. In the FET/diode cell structure, a SiC Schottky diode is used as the upper device to eliminate the reverse recovery, and the testing results show that the SiC MOSFET has 2.4 times higher switching loss than the Si CoolMOS. This can be explained by the smaller transconductance and the higher Miller voltage of the SiC MOSFET. On the other hand, the Si CooMOS has 10 times higher switching loss than the SiC MOSFET in the FET/FET cell structure because of the significant turn-on loss caused by the poor reverse recovery of its body diode.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downDue to the low availability, high cost, and limited performance of high voltage power devices in high voltage high power applications, series-connection of low voltage switches is commonly considered. Practically, because of the dynamic voltage unbalance and the resultant reliability issue, switches in series-connection are not popular, especially for fast switching field-effect transistors such as silicon (Si) super junction MOSFETs, silicon carbide (SiC) JFETs, SiC MOSFETs, and gallium nitride (GaN) HEMTs, since their switching performance is highly sensitive to gate control, circuit parasitics, and device parameters. In the end, slight mismatch can introduce severe unbalanced voltage. This paper proposes an active voltage balancing scheme, including 1) tunable gate signal timing unit between series-connected switches with <; 1 ns precision resolution by utilizing a high resolution pulse-width modulator (HRPWM) which has existed in micro-controllers; and 2) online voltage unbalance monitor unit integrated with the gate drive as the feedback. Based on the latest generation 600-V Si CoolMOS, experimental results show that the dynamic voltage can be automatically well balanced in a wide range of operating conditions, and more importantly, the proposed scheme has no penalty for high-speed switching.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downTo overcome the increased switching losses in high frequency power electronics, control-based modulation techniques such as boundary current mode (BCM) are commonly used in full bridge inverter and rectifier topologies to guarantee zero voltage switching (ZVS). Traditionally, in order to implement BCM modulation, a combination of current programmed mode (CPM) control and model-based techniques are used. The former is highly susceptible to noise and sensing delay, while the latter is subject to modeling error. In this work, a dual-current programmed mode (DCPM) control circuit for BCM operation is designed and implemented. The proposed control network achieves better noise immunity and low propagation delay at high frequency while regulating peak and valley currents in each period. The operation of this control scheme is demonstrated experimentally using a GaN-based half bridge inverter prototype.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downUnderstanding the CM inductor core saturation mechanism and reducing core flux density is critical for CM inductor design optimization. Instead of a time domain method, this paper introduces frequency domain spectrum concept for CM inductor core saturation analysis and design optimization, which will provide designers a better understanding of CM inductor design. First, both core permeability and converter modulation index's opposite influence on DM flux density and CM flux density are identified. Then, CM flux density is further investigated based on the spectrum concept. Three components in the CM inductor which may cause large CM flux density and core saturation are summarized: (1) switching frequency related components, (2) impedance resonance frequency related components, and (3) modulation frequency related components. Each component is investigated for CM flux density reduction and filter design optimization. A connecting AC and DC side midpoint with notch filter structure is proposed to reduce modulation frequency related components. Experiment results are presented to verify the proposed concept and method.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downAttenuation performance of an EMI filter can be significantly degraded by coupling, parasitics, and frequency-dependent nonlinearity of magnetic cores. In this paper, the effect due to mutual capacitive coupling in filter structures with T-shape joint is identified and investigated. Its mechanism indicates that this coupling is the dominant cause of performance degradation in T-shape filters. PCB slits and grounded shielding are proposed as two effective mitigation solutions, respectively, and are further combined to improve filter transfer gain up to 40 dB along the high frequency range. Experimental results obtained from a three-phase LCL common-mode (CM) filter verify the significant impact of this coupling and the effectiveness of the proposed mitigation methods.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downThis paper presents a modeling approach for dual active bridge (DAB) converter in electric vehicle (EV) applications which considers the magnetizing inductance effect of the high-frequency transformer. A Typical DAB transformer has very high magnetizing inductance compared to the leakage inductance. As a result, the magnetizing current can be neglected. However, for integrated and hybrid converters, where the same core is used for both DC excitation and AC excitation, an air gap is used to prevent core saturation. In such applications, the effect of magnetizing inductance needs to be considered for DAB converter modeling. For accurate estimation of the DAB converter, a loss model considering magnetizing inductance is developed in this paper. Finite element analysis (FEA) is performed to model the transformer to evaluate the proximity loss and fringe induced eddy current loss mechanisms. An experimental prototype of the DAB converter is developed to verify the proposed model. Experimental waveforms are presented and compared for different power level and switching frequency.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downSuperconducting technologies such as motors together with the supporting cryogenic power electronic system are growing in importance in aircraft applications. It is critical to understand the influence of low temperature on filters of the power converter system in these applications. Also, it is worthwhile to investigate whether the converter system can achieve higher efficiency and high power density by utilizing the provided low temperature cooling environment. This paper conducted a comprehensive magnetic core characterization at low temperature to understand the core properties and support filter design at low temperature. The ferrite and nanocrystalline material are characterized from room temperature to cryogenic temperature in a wide range of operating frequencies. The results show that the permeability of ferrite material decreases by a factor of 7~8 and the core loss increases more than 10 times when operating at very low temperature. The permeability of nanocrystalline material decreases to 60% and the core loss increases 1.5~2.5 times when operating at very low temperature. The saturation flux density of both materials has slight increase at low temperature. Based on tested data, a case study of inductor design considering the low temperature cooling environment is presented to illustrate the influence of low temperature on inductor design.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downTo operate a converter at cryogenic temperatures, understanding the characteristics of power semiconductor devices is critical. This paper presents the characterization of state-of-the-art 1.2 kV SiC MOSFETs from leading manufacturers at cryogenic temperatures. The testing setup consisting of a cryogenic chamber, and a liquid nitrogen Dewar is introduced. With a curve tracer and double pulse test, comprehensive characterization of the SiC MOSFETs including both static and switching performance is conducted and evaluated. Test results indicate the on-resistance increases while the breakdown voltage remains relatively constant at cryogenic temperatures. Other characteristics like threshold voltage and switching loss vary significantly at cryogenic temperatures among devices from different manufacturers.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downZero sequence circulating current (ZSCC) exists when paralleled inverters have common dc and ac sides without isolation. Most of the prior work on the ZSCC analysis and suppression depended on paralleled two-level inverters. The scenarios involved in the three-level converters are more complicated. This paper investigates the ZSCC in paralleled three-level active neutral point clamped (ANPC) inverters. The mechanisms causing potential ZSCC jump in three-level paralleled ANPC inverters are analyzed. The ZSCC patterns of different interleaved modulation schemes for three-level converters are illustrated. Then, the active vector dividing concept is extended to three-level converters, and a modulation scheme is proposed to reduce the high frequency ZSCC in three-level converters. Experiments have been conducted on two paralleled three-level inverters. The current jump in ZSCC is observed and mitigated. The ZSCC with proposed modulation scheme is reduced to less than half of the ZSCC with conventional continuous space vector modulation (CSVM) scheme.
[BibTeX]2018 IEEE Applied Power Electronics Conference and Exposition (APEC)2018
arrow_drop_downUnlike conventional passive or active filters, an impedance balancing circuit reduces the common-mode (CM) electromagnetic interference (EMI) noise by establishing an impedance balancing bridge. The EMI noise can be significantly reduced when the impedance bridge is designed to be well balanced. This paper investigates impedance balancing circuits in Dc-fed motor drive systems where both DC input and AC output need to meet EMI standards and thus EMI filters are needed for both sides. An impedance balancing circuit is proposed to reduce both DC and AC side CM noise. Two auxiliary branches are added to the conventional passive filters to establish an impedance bridge and reduce CM noise. The design criteria are presented, and the impact of the proposed impedance balancing circuit on both sides CM noise are investigated. It shows that the proposed impedance balancing circuit can reduce DC side and AC side CM noise based on different mechanisms. The CM noise reduction performance of the proposed method does not depend on the motor and cable models. Experiment results are presented to demonstrate the feasibility and effectiveness of the proposed method.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downOne of the popular converter topologies applied in high power dc-ac applications is the three-level active neutral point clamped (ANPC). Owing to relatively low switching frequency and slow switching speed of these topologies in high power applications, the commutation loop analysis in these topologies has not been fully conducted, and the over-voltage issue of non-active switches has not been thoroughly analyzed. This paper reveals an over-voltage issue on non-active switches in three level inverters due to multi-commutation loop. The detailed mode analysis during the commutation and related over-voltage issue are given. Finally, Si-based ANPC with 140 kHz switching frequency and SiC-based ANPC converters with 280 kHz switching frequency and high switching speed are tested respectively to compare and verify the over-voltage issue for non-active switches.
[BibTeX]2018 IEEE Energy Conversion Congress and Exposition (ECCE)2018
arrow_drop_downIn order to evaluate the feasibility of newly developed GaN devices in a cryogenic-cooled converter, this paper characterizes a 650 V enhancement-mode Gallium-Nitride heterojunction field-effect transistor (GaN HFET) at cryogenic temperatures. The characterization includes two parts: static and dynamic characterization. The results show that this GaN HEMT is an excellent device candidate to be applied in cryogenic-cooled applications. For example, transconductance at cryogenic temperature is 2.5 times of one at room temperature, and accordingly, peak di/dt during turn-on transients at cryogenic temperature is around 2 times of that at room temperature. Moreover, the on-resistance of the channel at cryogenic temperature is only one-fifth of that at room temperature.
[BibTeX]2017 IEEE Applied Power Electronics Conference and Exposition (APEC)2017
arrow_drop_downA new single-stage AC/RF converter is proposed which directly converts a utility AC input to a regulated, high frequency (6.78MHz) AC output for wireless power transmission. The topology integrates a totem pole rectifier operating in discontinuous conduction mode (DCM) and a phase-shift controlled full bridge inverter. Compared to traditional multi-stage approaches, the single-stage approach improves system power efficiency by reducing the number of cascaded conversion stages. In addition, the reduced power semiconductor component count will be a potential benefit for compact size and lower cost. A 100W laboratory prototype has been built to verify theoretical analysis. Experimental measurements show the capability of the converter to provide power factor correction (PFC) with high conversion efficiency and low total harmonic distortion (THD).
[BibTeX]2017 IEEE Applied Power Electronics Conference and Exposition (APEC)2017
arrow_drop_downBattery charging circuits for mobile applications, such as smart phones and tablets, require both small area and low losses. In addition, to reduce the charging time, high current is needed through the converter. In order to reduce conduction losses, low on-resistance of the switches is necessary. However, specific resistance (resistance per unit area) is a strong function of the maximum voltage blocking capability of the transistors. To maintain high efficiency and ensure device reliability, the designed breakdown voltage of the transistors needs to include some margin to account for ringing on the switching node. Bond wires add inductance to the power loop increasing the overshoot voltage. In this work the design, implementation and testing of a 40 W CMOS integrated buck converter with an on chip decoupling capacitor are presented. The design was optimized for a 5V to 4V application with a maximum of 2 W on-chip losses at 10 A with an operating frequency of 1 MHz.
[BibTeX]2017 IEEE 5th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)2017
arrow_drop_downThis paper introduces a dead-time optimization technique for a 2-level voltage source converter (VSC) using turn-off transition monitoring. Dead-time in a VSC impacts power quality, reliability, and efficiency. Silicon carbide (SiC) based VSCs are more sensitive to dead-time from increased reverse conduction losses and turn-off time variability with operating conditions and load characteristics. An online condition monitoring system for SiC devices has been developed using gate drive assist circuits and a micro-controller. It can be leveraged to monitor turn-off time and indicate the optimal dead-time in each switching cycle of any converter operation. It can also be used to specify load current polarity, which is needed for dead-time optimization in an inverter. This is an important distinction from other inverter dead-time elimination/optimization schemes as current around the zero current crossing is hard to accurately detect. A 1kW half-bridge inverter was assembled to test the turn-off time monitoring and dead-time optimization scheme. Results show 91% reduction in reverse conduction power losses in the SiC devices compared to a set dead-time of 500ns switching at 50 kHz.
[BibTeX]Operating mode transition control of a SiC integrated DC DC powertrain charger for electric vehicles2017 IEEE Transportation Electrification Conference and Expo (ITEC)2017
arrow_drop_downIn this paper, a control strategy of an integrated, reconfigurable DC-DC converter for plugin electric vehicles (EVs) is proposed. The integrated converter, capable of operating in both traction and charging modes, can be reconfigured as an interleaved boost or a dual active bridge (DAB) converter. The existing contactors of the battery management system (BMS) are used for reconfiguration between the boost and DAB modes. To maximize overall power conversion efficiency during traction operation, the converter is dynamically reconfigured to operate in the mode with highest efficiency at the present operating point. A switching transition control approach is developed for fast and seamless switching, ensuring zero-voltage turn-on and zero-current turn-off of the BMS contactors. The smooth transitions minimize switching-induced degradation of the BMS contactors, and allow uninterrupted power delivery during mode transitions. The experimental results of the prototype are presented to verify the functionality of the proposed control approach.
[BibTeX]2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL)2017
arrow_drop_downThis work presents an analytical model for integrated DC-DC converters at high currents. A loss model is constructed using parameters extracted from simulation or are available in the process manual and are scaled with the size of the device. The loss model is used to compare power converter implementations for varying on-chip size and power loss goals. Buck, 3-Level Buck, and Switched-Capacitor topologies are compared using this analytical model and then implemented in a commercial CMOS process. Validation of the constructed loss model is done through hardware measurements.
[BibTeX]2017 IEEE Applied Power Electronics Conference and Exposition (APEC)2017
arrow_drop_downWhile fast switching brings many benefits, it also presents unwanted ringing during switching transient. In this paper, an increasing magnitude ringing phenomenon is observed during the MOSFET turn-off transient. The unusual phenomenon is replicated in simulation and it is found the MOSFET channel is turned on again after it is turned off. The major cause to this unexpected turn on is found to be common source inductance and a moderate 3 nH one in simulation replicates the severe self-turn-on ringing observed in experiment. This paper reveals the detrimental effect of common source inductance in fast switching. Therefore, Kelvin source connection in circuit and package design is strongly recommended.
[BibTeX]