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Daniel Costinett

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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 an Assistant 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 power supplies, wireless power transfer, energy harvesting, biomedical devices, and electric vehicles.

Publications


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Journal Papers
Title
Year
  • Bo Liu; Ren Ren; Zheyu Zhang; Ben Guo; Fei Wang; Daniel Costinett
    CPSS Transactions on Power Electronics and Applications
    2018

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    A 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.

  • Bo Liu; Ren Ren; Edward A. Jones; Fred Wang; Daniel Costinett; Zheyu Zhang
    IEEE Transactions on Power Electronics
    2018

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    Wide 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.

  • Weimin Zhang; Fred Wang; Daniel J. Costinett; Leon M. Tolbert; Benjamin J. Blalock
    IEEE Transactions on Power Electronics
    2017

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    Newly 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.

  • Yutian Cui; Fei Yang; Leon M. Tolbert; Daniel J. Costinett; Fred Wang; Benjamin J. Blalock
    IEEE Transactions on Power Electronics
    2017

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    With 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.

  • Zheyu Zhang; Jeffery Dix; Fei Fred Wang; Benjamin J. Blalock; Daniel Costinett; Leon M. Tolbert
    IEEE Transactions on Power Electronics
    2017

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    This 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.

  • Zheyu Zhang; Haifeng Lu; Daniel J. Costinett; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock
    IEEE Transactions on Power Electronics
    2017

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    Dead 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).

  • Chongwen Zhao; Daniel Costinett
    IEEE Transactions on Industrial Electronics
    2017

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    Multifrequency 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.

  • Zhiqiang Wang; Xiaojie Shi; Leon M. Tolbert; Fred Wang; Zhenxian Liang; Daniel Costinett; Benjamin J. Blalock
    IEEE Transactions on Power Electronics
    2016

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    This 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.

  • Edward A. Jones; Fei Fred Wang; Daniel Costinett
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2016

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    Gallium 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 R<sub>ds,on</sub>, 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.

  • Chongwen Zhao; Bradford Trento; Ling Jiang; Edward A. Jones; Bo Liu; Zheyu Zhang; Daniel Costinett; Fei Fred Wang; Leon M. Tolbert; John F. Jansen; Reid Kress; Rick Langley
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2016

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    High 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.

  • Ren Ren; Bo Liu; Edward A. Jones; Fei Fred Wang; Zheyu Zhang; Daniel Costinett
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2016

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    Gallium 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.

  • Michael Evzelman; M. Muneeb Ur Rehman; Kelly Hathaway; Regan Zane; Daniel Costinett; Dragan Maksimovic
    IEEE Transactions on Power Electronics
    2016

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    Electric-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.

  • Daniel Costinett; Dragan Maksimovic; Regan Zane
    IEEE Transactions on Power Electronics
    2015

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    Nonlinear, 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.

  • Zheyu Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    IEEE Transactions on Power Electronics
    2015

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    Double 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.

  • Zhiqiang Wang; Xiaojie Shi; Leon M. Tolbert; Fei (Fred) Wang; Zhenxian Liang; Daniel Costinett; Benjamin J. Blalock
    IEEE Transactions on Power Electronics
    2015

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    This 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.

  • Daniel Costinett; Dragan Maksimovic; Regan Zane
    IEEE Transactions on Power Electronics
    2013

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    A 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.

  • Daniel Costinett; Miguel Rodriguez; Dragan Maksimovic
    IEEE Transactions on Power Electronics
    2013

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    This 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.

  • Zoya Popović; Erez Avigdor Falkenstein; Daniel Costinett; Regan Zane
    Proceedings of the IEEE
    2013

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    This 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/cm2range, 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.

  • Erez Falkenstein; Daniel Costinett; Regan Zane; Zoya Popovic
    IEEE Transactions on Circuits and Systems II: Express Briefs
    2011

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    This 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.

Conference Papers
Title
Year
  • Jie Li; Daniel Costinett
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    A 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.

  • Jacob Dyer; Zheyu Zhang; Fred Wang; Daniel Costinett; Leon M. Tolbert; Benjamin J. Blalock
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    Dead-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.

  • Jordan Sangid; GaVin Long; Parker Mitchell; Benjamin J. Blalock; Daniel J. Costinett; Leon M. Tolbert
    2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2018

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    This 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.

  • Ling Jiang; Daniel Costinett
    2018 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow)
    2018

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    A 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.

  • Bo Liu; Ren Ren; Zheyu Zhang; Fred Wang; Daniel Costinett
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    As 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.

  • Yutian Cui; Leon M. Tolbert; Daniel J. Costinett; Fred Wang; Benjamin J. Blalock
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    Data 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.

  • Jie Li; Daniel Costinett
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    The 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.

  • Ling Jiang; Daniel Costinett
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    A 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.

  • Wen Zhang; Zheyu Zhang; Fred Wang; Daniel Costinett; Leon M. Tolbert; Benjamin J. Blalock
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    Switching 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.

  • Gabriel Gabian; Jordan Gamble; Benjamin Blalock; Daniel Costinett
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    In 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.

  • Chongwen Zhao; Daniel Costinett; Songnan Yang
    2018 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow)
    2018

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    In 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.

  • Spencer Cochran; Daniel Costinett
    2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2018

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    Resonant 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.

  • Handong Gui; Zheyu Zhang; Ren Ren; Ruirui Chen; Jiahao Niu; Leon M. Tolbert; Fred Wang; Benjamin J. Blalock; Daniel J. Costinett; Benjamin B. Choi
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    Although 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.

  • Kamal Sabi; Daniel Costinett
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    To 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.

  • Ruirui Chen; Zheyu Zhang; Ren Ren; Jiahao Niu; Handong Gui; Fred Wang; Leon M. Tolbert; Daniel J. Costinett; Benjamin J. Blalock
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    Understanding 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.

  • Bo Liu; Ren Ren; Fred Wang; Daniel J. Costinett; Zheyu Zhang; Yiwei Ma
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    Attenuation 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.

  • Zheyu Zhang; Handong Gui; Jiahao Niu; Ruirui Chen; Fred Wang; Leon M. Tolbert; Daniel J. Costinett; Benjamin J. Blalock
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    Due 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 &lt;; 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.

  • Saeed Anwar; Daniel Costinett
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    This 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.

  • Ruirui Chen; Zhou Dong; Zheyu Zhang; Handong Gui; Jiahao Niu; Ren Ren; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett; Benjamin B. Choi
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    Superconducting 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.

  • Handong Gui; Ren Ren; Zheyu Zhang; Ruirui Chen; Jiahao Niu; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett; Benjamin B. Choi
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    To 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.

  • Ruirui Chen; Jiahao Niu; Zheyu Zhang; Handong Gui; Ren Ren; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett; Benjamin B. Choi
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    Zero 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.

  • Ruirui Chen; Zheyu Zhang; Ren Ren; Jiahao Niu; Handong Gui; Fred Wang; Leon M. Tolbert; Daniel J. Costinett; Benjamin J. Blalock
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    Unlike 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.

  • Ren Ren; Zheyu Zhang; Bo Liu; Ruirui Chen; Handong Gui; Jiahao Niu; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett; Benjamin B. Choi
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    One 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.

  • Zheyu Zhang; Handong Gui; Ren Ren; Fred Wang; Leon M. Tolbert; Daniel J. Costinett; Benjamin J. Blalock
    2018 AIAA/IEEE Electric Aircraft Technologies Symposium (EATS)
    2018

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    Wide 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.

  • Ren Ren; Handong Gui; Zheyu Zhang; Ruirui Chen; Jiahao Niu; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett; Benjamin B. Choi
    2018 IEEE Energy Conversion Congress and Exposition (ECCE)
    2018

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    In 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.

  • Jared A. Baxter; Daniel A. Merced; Daniel J. Costinett; Leon M. Tolbert; Burak Ozpineci
    2018 IEEE Transportation Electrification Conference and Expo (ITEC)
    2018

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    Automated 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.

  • Ling Jiang; Daniel Costinett; Aly Fathy; Songnan Yang
    2017 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2017

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    A 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).

  • Gabriel Gabian; Benjamin Blalock; Daniel Costinett
    2017 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2017

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    Battery 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.

  • Saeed Anwar; Daniel J. Costinett
    2017 IEEE Transportation Electrification Conference and Expo (ITEC)
    2017

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    In 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.

  • Gabriel Gabian; Jordan Gamble; Benjamin Blalock; Daniel Costinett
    2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2017

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    This 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.

  • Wen Zhang; Zheyu Zhang; Fred Wang; Daniel Costinett; Leon Tolbert; Benjamin Blalock
    2017 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2017

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    While 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.

  • Spencer Cochran; Daniel Costinett
    2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2017

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    With the growth of magnetic resonance wireless power transfer (WPT), the WPT field sees a push toward higher operating frequencies. New challenges arise as the fundamental frequency increases, namely the relevance of circuit parasitics and the difficulty in preventing harmonic distortion. A 6.78 MHz synchronous rectifier is shown to address the issues of total harmonic distortion (THD) and dynamic loading. This work focuses on further modeling the proposed rectifier, accounting for parasitic conduction losses, THD, input phase control, and characterization of design trade offs. The updated model includes both an exact solution for the complete dynamics of the dead time resonance which, by design, has significant impact on converter harmonics, impedance, and power delivery. The model is compared to the simpler model from previous work and is verified via experimental results.

  • Chongwen Zhao; Daniel Costinett
    2017 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2017

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    Concurrent dual-frequency ac outputs from a single-inverter configuration potentially benefit many industrial applications, such as induction heating and wireless power transfer. In this paper, a phase-shift dual-frequency selective harmonic elimination (DFSHE) method is proposed to simultaneously generate and regulate two ac outputs at different frequencies from a single full-bridge inverter, which expands the family of DFSHEs. With the phase shift operation, all triplen harmonics of the fundamental are inherently suppressed in the inverter output spectrum, which improves the output THD, and may ease filter design. In addition, an evaluation of the unipolar, bipolar and phase-shift DFSHE techniques is presented, which analyzes design tradeoffs for multi-frequency applications. Finally, experimental results from a 50 W dual-output inverter validate the effectiveness of the proposed method, which agree with theoretical predictions and simulation results.

  • Zheyu Zhang; Craig Timms; Jingyi Tang; Ruirui Chen; Jordan Sangid; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    2017 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2017

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    Cooling a converter to low temperatures, e.g. using cryogenic cooling, can significantly improve the efficiency and density of a power conversion system. For the development and optimization of a cryogenically-cooled converter, an understanding of power semiconductor characteristics is critical. This paper focuses on the characterization of high-voltage, high-speed switching, power semiconductors at cryogenic temperature. First, the testing setup for cryogenic temperature characterization is introduced. Three testing setups are established for cryogenic switch characterization, including: 1) on-state resistance and forward voltage drop of the body diode, 2) leakage current and breakdown voltage, and 3) switching characteristics. For each testing set up, the corresponding testing configurations, hardware setups, and practical considerations are summarized. Additionally, the test results at cryogenic temperature are illustrated and analyzed for 650-V Si CoolMOS. It is then demonstrated that when the cryogenic temperature test results are compared to that of room temperature, the device performance varies significantly; for example: on-state resistance reduces by 63%, breakdown voltage drops by 31%, switching time decreases and switching energy loss decreases by 26%. Furthermore, the peak dv/dt during transient switching at cryogenic temperature exceeds 100 V/ns which is comparable to the emerging wide bandgap Gallium Nitride devices.

  • Jacob Dyer; Zheyu Zhang; Fred Wang; Daniel Costinett; Leon M. Tolbert; Benjamin J. Blalock
    2017 IEEE 5th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2017

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    This 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.

  • Bo Liu; Ren Ren; Edward Jones; Fred Wang; Daniel Costinett; Zheyu Zhang
    2016 IEEE Energy Conversion Congress and Exposition (ECCE)
    2016

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    Wide bandgap (WBG) semiconductors owing to their low loss and high switching capability, are gradually adopted in high power-density high efficiency applications, and impose new challenges from control to hardware design. In this paper, a Gallium Nitride (GaN) HEMT plus SiC diode based Vienna type rectifier is proposed to serve as the power factor correction stage for a high-density battery charger system. To meet low current harmonic requirement, PWM voltage distortion during turn-off transition, found as the main harmonics contributor, is studied. The distortion mechanism led by different parasitic capacitances of WBG devices is presented. A mitigation scheme is thereafter proposed considering their nonlinear voltage-dependent characteristics and eventually deduced from a pulse-based turn-off compensation to a generic modulation correction. Simulation and experimental results through a 450 kHz enhancement-mode GaN based Vienna type rectifier finally demonstrate the high performance of the proposed approach, showing a THD reduction up to 7% with a relatively low-speed control.

  • Douglas W. Bouler; Jared Baxter; Daniel Costinett
    2016 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
    2016

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    This paper presents a method of optimizing low power boost converters for use in far-field wireless energy harvesting systems. This method uses a database of manufacturer-provided device characteristics of both Silicon and GaN FETs to construct Figures of Merit (FOMs) used for evaluating device technologies for power loss based on boost converter parameters. A loss model is constructed for predicting device power losses and system efficiency over a wide range of operating points. Using the analysis framework, an asynchronous boost converter is constructed and experimentally verified with operation as low as 10 μW with a peak efficiency of 74% at an input power of 300 μW.

  • Richard Kyle Harris; Benjamin M. McCue; Benjamin D. Roehrs; Charles Roberts; Benjamin J. Blalock; Daniel J. Costinett; Kouros Sariri; George Megyei; Cheng-Po Chen; Avinash Kashyap; Reza Ghandi
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    The properties of silicon carbide (SiC) integrated circuit (IC) processes are discussed and nonlinear-carrier control is proposed as a controller topology that can work within the design challenges presented by SiC. A boost converter with NLC controller is demonstrated using circuit blocks built with SiC IC models.

  • Zheyu Zhang; Fred Wang; Daniel J. Costinett; Leon M. Tolbert; Benjamin J. Blalock; Xuanlyu Wu
    2016 IEEE Energy Conversion Congress and Exposition (ECCE)
    2016

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    Junction temperature is a critical indicator for health condition monitoring of power devices. Concerning the reliability of emerging silicon carbide (SiC) power semiconductors due to immaturity of new material and packaging, junction temperature measurement becomes more significant and challenging, since SiC devices have low on-state resistance, fast switching speed, and high susceptibility to noise and parasitics in circuit implementations. This paper aims at developing a practical and cost-effective approach for online junction temperature monitoring of SiC devices using turn-off delay time as the thermo-sensitive electrical parameter (TSEP). The sensitivity is analyzed for fast switching SiC devices. A gate impedance regulation assist circuit is designed to improve the sensitivity by a factor of 60 and approach hundreds of ps/°C in the case study with little penalty of the power conversion performance. Also, an online monitoring system based on three gate assist circuits is developed to monitor the turn-off delay time in real time with the resolution within hundreds of ps. In the end, the micro-controller is capable of “reading” junction temperature during the converter operation with less than 0.5 °C measurement error. Two testing platforms for calibration and online junction temperature monitoring are constructed, and experimental results demonstrate the feasibility and accuracy of the proposed approach. Furthermore, the proposed gate assist circuits for sensitivity improvement and high resolution turn-off delay time measurement are transistor based and suitable for chip level integration.

  • Zheyu Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    High speed switching of WBG devices causes their switching behavior to be highly susceptible to the parasitics in the circuit, including inductive loads. An inductive load consisting of a motor and power cable significantly worsens the switching speed and losses of SiC MOSFETs in a PWM inverter. This paper focuses on the motor plus power cable based inductive load, and aims at mitigating its negative influence during the switching transient. An auxiliary filter is designed and inserted between the converter and inductive load so that the parasitics of the load will not be “seen” from the converter side during the switching transient. Test results with Cree 1200-V/20-A SiC MOSFETs show that the proposed auxiliary inductor enables the switching performance with a practical inductive load (e.g., motor plus cable based inductive load) to exhibit behavior close to that when the optimally-designed double pulse test load inductor is employed.

  • Chongwen Zhao; Daniel Costinett; Brad Trento; Daniel Friedrichs
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    Simultaneous generation of two AC outputs at different frequencies from a single-phase inverter offers practical benefits and control flexibility for many industrial applications. In this paper, a dual-frequency selective harmonic elimination (DFSHE) modulation method is proposed to generate and control two individual frequencies in an H-bridge, while diminishing undesired harmonics. Two AC elements are synthesized independently in the modulation scheme, and thus flexible individual power regulation is achieved via the proposed method. In addition, both unipolar and bipolar DFSHE cases are investigated. Characteristics of the two methods are compared and alternatives are provided for different applications. The generation algorithms of the DFSHE are also studied in this paper, and can be applied to a variety of DC/AC topologies without adding extra switching devices. Finally, the experimental results from a 100W dual-load single-phase inverter verify the effectiveness of proposed method, where 50 kHz and 450 kHz AC outputs are generated and individually regulated.

  • Ren Ren; Bo Liu; Edward A. Jones; Fred Wang; Zheyu Zhang; Daniel Costinett
    2016 IEEE Energy Conversion Congress and Exposition (ECCE)
    2016

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    Due to the realization of zero voltage switching (ZVS) under the full load range, LLC resonant converter is widely adopted in the telecom, battery charger and several applications, characterized with high efficiency, high frequency and high power density, to realize DC conversion. Recently, by using Gallium Nitride (GaN) HFETS, switching frequency of LLC converters is further increased. However, ZVS failure cannot be predicted accurately in the high switching frequency condition by only considering traditional constraints generally applied in the low frequency design. The traditional constraints result in a too optimistic estimation of the dead time to obtain ZVS without considering the reverse resonance under the dead time and the design of resonant parameters at high resonant frequency and high load condition. The experiment shows the LLC converter loses ZVS even through the converter satisfies the ZVS constraints proposed by previous paper. In this paper, the failure mode will be investigated in detail and an accurate ZVS boundary is proposed for high frequency LLC converter design. The proposed theory was verified on a 1 MHz, 1500 W LLC prototype.

  • Spencer Cochran; Farhan Quaiyum; Aly Fathy; Daniel Costinett; Songnan Yang
    2016 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
    2016

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    This work examines the potential of a GaN-based synchronous rectifier as a receiver in 6.78 MHz wireless power transfer (WPT) applications. Compared to a traditional diode-based rectifier, the synchronous rectifier has merits in its additional control freedoms. The active control of switching actions can be used to alter impedance presented to transmitting source, or, when combined with a zero-voltage switching (ZVS) resonant tank, to reduce harmonics generated by the switching actions, and therefore mitigate requirements on the filter network to meet EMI limitations. Analysis of control and hardware design strategies to maximize efficiency, limit total harmonic distortion (THD), and control impedance at the WPT frequency are presented and verified on a prototype experimental platform.

  • Edward A. Jones; Fred Wang; Daniel Costinett; Zheyu Zhang; Ben Guo
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    Enhancement-mode GaN HFETs enable efficient high-frequency converter design, but this technology is relatively new and exhibits different characteristics from Si or SiC MOSFETs. GaN performance at elevated temperature is especially unique. Turn-on time increases significantly with temperature, and turn-on losses increase as a result. This phenomenon can be explained based on the relationships between junction temperature and GaN device transconductance, and between transconductance and turn-on time. An analytical relationship between temperature and turn-on loss has been derived for the 650-V GS66508 from GaN Systems, and verified with experimental results. Based on this relationship, a detailed model is developed, and a simplified scaling factor is proposed for estimating turn-on loss in e-mode GaN HFETs, using room-temperature switching characterization and typically published datasheet parameters.

  • Yutian Cui; Weimin Zhang; Leon M. Tolbert; Daniel J. Costinett; Fred Wang; Benjamin J. Blalock
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    In this paper, a single stage system which converts 400 V to 1 V within one stage and performs as the high voltage point of load (HV POL) converter for data centers is proposed. A load dependent soft switching method has been proposed for half bridge current doubler with simple auxiliary circuit. The operation principles of the soft switching converter have been analyzed in detail. A lossless RCD current sensing method is used to sense the output current value to reduce the auxiliary circuit loss and turn off loss of secondary side devices as load reduces to achieve higher efficiency. Experimental efficiency has been tested to prove the proposed method can increase the converter's efficiency in both heavy and light load condition. A prototype of the half bridge current doubler circuit has been built to verify the theory.

  • Saeed Anwar; Weimin Zhang; Fred Wang; Daniel J. Costinett
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    In this paper, an integrated, reconfigurable DC-DC converter for plugin and hybrid Electric Vehicles (EV) is proposed. The converter integrates functionality for both EV powertrain and charging operation into a single unit. During charging, the proposed converter functions as a DAB converter, providing galvanic isolation. For powertrain operation, the converter functions as an interleaved boost converter. During light load powertrain operation, the efficiency of the converter can be further improved by employing the integrated DAB. The proposed integrated converter does not require any extra relays or contactors for charging and powertrain operation. By using such integration, the overall volume and weight of the power electronics circuits, passives and associated cooling system can be improved. In addition, the power flow efficiency from EV battery to the high voltage DC bus for the motor inverter can be improved. The experimental results of the prototype are presented to verify the functionality of the proposed converter.

  • Ling Jiang; Daniel Costinett
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    In this paper, a triple active bridge converter is proposed. The topology is capable of achieving ZVS across the full load range with wide input voltage while minimizing heavy load conduction losses to increase overall efficiency. This topology comprises three full bridges coupled by a three-winding transformer. At light load, by adjusting the phase shift between two input bridges, all switching devices can maintain ZVS due to a controlled circulating current. At heavy load, the two input bridges work in parallel to reduce conduction loss. The operation principles of this topology are introduced and the ZVS boundaries are derived. Based on analytical models of power loss, a 200W laboratory prototype has been built to verify theoretical considerations.

  • Ren Ren; Bo Liu; Edward A. Jones; Fred Wang; Zheyu Zhang; Daniel Costinett
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    Gallium Nitride (GaN) HFETS 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 V or 270 V, selected with a jumper, which meets the two most common dc bus voltages 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 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 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 low switching loss. Also, the converter utilizes the matrix transformer with resonant parameters designed to avoid ZVS failure. The operation principle of the converter is analyzed and verified on a 1MHz resonant frequency prototype.

  • Jacob Dyer; Zheyu Zhang; Fred Wang; Daniel Costinett; Leon M. Tolbert; Benjamin J. Blalock
    2016 IEEE 4th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2016

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    Many intelligent gate drivers being designed for new state-of-the-art WBG devices typically only focus on protection and driving capabilities of the devices. This paper introduces an intelligent gate driver that incorporates online condition monitoring of the WBG devices. For this specific case study, three timing conditions (turn-off delay time, turn-off time, and voltage commutation time) of a silicon carbide (SiC) device are online monitored. This online monitoring system is achieved through gate driver assist circuits and a micro-controller. These conditions are then utilized to develop converter-level benefits for the converter application the SiC devices are placed in. Junction temperature monitoring is realized through turn-off delay time monitoring. Dead-time optimization is achieved with turn-off time monitoring. Dead-time compensation is obtained with turn-off time and voltage commutation time monitoring. The case study converter assembled for testing purposes is a half-bridge inverter using two SiC devices in a phase-leg configuration. All timing conditions are correctly monitored within reasonable difference of the actual condition time. A calibration curve was created to give a direct relationship between turn-off delay time and junction temperature. The half-bridge inverter can operate at 600 Vdc input and successfully obtain a junction temperature measurement through monitored t<sub>d_off</sub> and the calibration curve. Furthermore, the proposed online condition monitoring system is transistor based and suitable for the chip level integration, enabling this practical approach to be cost-effective for end users.

  • Ling Jiang; Farshid Tamjid; Chongwen Zhao; Daniel Costinett; Aly Fath; Songnan Yang
    2016 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
    2016

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    A two-stage power conversion architecture for the transmitter in wireless power transfer applications is introduced. The system achieves high efficiency at output powers up to 100W, and exhibits constant output current over varying load impedance. A front-end bridgeless totem pole rectifier provides power factor correction (PFC), necessary at the designed power level. This rectifier achieves high efficiency by eliminating the conventional diode full bridge and by achieving soft switching operation. A full bridge inverter, switching at 6.78MHz, generates the AC output. Combined with an output passive filter network, the inverter achieves constant output current with load variation without the need for dynamic feedback control. A prototype system is constructed and tested experimentally to verify operation.

  • Chongwen Zhao; Daniel Costinett
    2016 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
    2016

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    Multi-frequency wireless power transfer (WPT) is advantageous in facilitating compatibility with different WPT standards. However, implementing a multi-frequency 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 multi-frequency programmed pulse width modulation (MFPWM) scheme. This dual-frequency modulated inverter can simultaneously generate and regulate 100 kHz and 6.78 MHz outputs, which facilitates the development of multi-standard WPT technology for consumer electronics. In addition, the principle of the proposed modulation is illustrated, where two different frequencies are concurrently modulated in the programmed pulse train of square waveforms, while eliminating certain harmonics in between. Design tradeoffs and constraints are examined through analytical circuit models. Finally, experimental results are provided to verify the effectiveness of the proposed WPT system.

  • Yutian Cui; Weimin Zhang; Leon M. Tolbert; Daniel J. Costinett; Fred Wang; Benjamin J. Blalock
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    High voltage DC (400 V) power supply architecture is becoming a standard in today's data center power supply. To further convert from 400 V to 1 V, usually several power stages are connected in series. Therefore, even if the efficiency of each power stage is high; the overall system efficiency is limited because of the multiplication of each converter's efficiency. In this paper, a single power stage system which converts 400 V to 1 V directly and performs as the high voltage point of load (HV POL) is proposed. A multi-phase interleaved phase shift pulse width modulation (PWM) DC/DC converter with input series and output parallel (ISOP) connection is selected as the power stage topology. A simplified two phase connected system is discussed in this paper. Common duty cycle control technique is used to control the ISOP connected converters. Input voltage sharing and output current sharing is analyzed with different types of mismatches in the circuit. Finally, the preliminary testing results are given.

  • Weimin Zhang; Yutian Cui; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    This paper investigates the Gallium Nitride (GaN) devices benefits on the LLC resonant DC-DC converter. First, the relationship between the device parameters and converter current based on an analytical loss model of LLC resonant converter has been established. After that, the loss analysis and comparison between Si-based and GaN-based converter is presented. The GaN-based design demonstrates about 40% loss reduction compared with the Si-based design. An insight on the extra winding loss due to the asymmetrical primary side and secondary side current is presented. The extra winding loss is reduced by 18% with GaN device application. The overall loss breakdown and the experimental result show the 20% overall loss reduction of the GaN-based LLC converter compared with the Si-based LLC converter.

  • Yu Long; Weimin Zhang; Daniel Costinett; Benjamin B Blalock; Luke L Jenkins
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    A novel resonant gate driver designed for the high-frequency enhancement-mode GaN HEMT power devices is proposed in this work. Simulation results indicate that it reduces gate driving loss more than 50% compared to the conventional non-resonant gate driving topology, and by 20% compared to the existing GaN resonant gate driver. The loss reduction is achieved by partially recovering gate charge to the supply during charging and discharging through a resonant process using an inductance in the gate loop. The resonant condition is managed using the desired turn-on and turn-off driving pulses at the input with specific driving time and pulse width control. These inputs also generate on-chip control signals for safely clamping the GaN power devices during the remaining switching cycle after the resonant transition has concluded. Simulations reveal improved switching waveforms using the proposed gate driver compared to the existing GaN resonant gate driving topologies.

  • Edward A. Jones; Fred Wang; Daniel Costinett; Zheyu Zhang; Ben Guo
    2015 IEEE 3rd Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2015

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    Cross conduction is a well-known issue in buck converters and phase-leg topologies, in which fast switching transients cause spurious gate voltages in the synchronous device and a subsequent increase in switching loss. Cross conduction can typically be mitigated with a well-designed gate drive, but this is challenging with WBG devices. Phase legs using SiC and GaN devices can experience heavy cross conduction loss due to their exceptionally fast switching transients. Enhancement-mode GaN heterojunction field-effect transistors (HFETs) in the 600-V class are now commercially available, with switching transients as fast as 200 kV/μs. A double pulse test setup was used to measure the switching loss of one such GaN HFET, with several gate drive circuits and resistances. The results were analyzed and compared to characterize the effects of cross conduction in the active and synchronous devices of a phase-leg topology with enhancementmode GaN HFETs.

  • Zheyu Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    This paper presents an active gate driver for Silicon Carbide (SiC) devices to fully utilize their potentials 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 the gate voltages and gate loop impedances of both devices in a phase-leg during different switching transients. Compared to a conventional gate driver, the proposed circuit has the capability of increasing the switching speed of the phase-leg power devices, suppressing the cross-talk to below device limits. Based on CREE's 2nd generation 1200-V SiC MOSFETs, the test results demonstrate the effectiveness of this active gate driver under various operating conditions. The switching time decreases by up to 28% during turn-on and 50% during turn-off in the prototype circuit, resulting in up to 31% reduction in switching energy loss. In addition, spurious gate voltages induced by cross-talk are limited within the required range.

  • Zheyu Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    2015 IEEE 3rd Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2015

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    Four factors impact high speed switching of silicon carbide (SiC) devices in voltage source converters, including limited gate driving capability, cross-talk, parasitics associated in switching loop, and parasitics of inductive load. This paper focuses on a solution to mitigate the adverse impact of the aforementioned factors. First, an intelligent gate drive is developed for gate driving capability enhancement and cross-talk suppression. Second, placement and layout design of power devices, gate drive, and power stage board are proposed to minimize parasitics for fast switching and over-voltage mitigation. Third, an auxiliary filter is designed to mitigate the negative impact of inductive load's parasitics during the switching transient. Finally, by utilizing all techniques developed above, a three-phase voltage source inverter with Cree 1200-V/20-A SiC MOSFETs is established. Test results show that the switching behavior of SiC devices in actual three-phase voltage source inverter fed motor drives can mostly repeat the switching performance tested by the optimally-designed double pulse test.

  • Yutian Cui; Weimin Zhang; Leon M. Tolbert; Daniel J. Costinett; Fred Wang; Benjamin J. Blalock
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    In this paper, the design of a high step down ratio (66:1) phase shift full bridge (PSFB) DC/DC converter used for data center power supplies in terms of primary side MOSFETs selection is covered. A detailed analysis of the converter's operation considering the impact of the output junction capacitance of primary side MOSFETs on the current RMS value has been performed. The study shows that a smaller output junction capacitance will lead to a smaller RMS current value on both primary and secondary side. For the high step down phase shift full bridge converter, transformer winding loss is the dominant loss; the reduction of current through the transformer will lead to a higher efficiency of the whole converter. This phenomenon is observed in experimental waveforms, and its impact on the converter's efficiency is also validated through experiment.

  • Edward A. Jones; Fred Wang; Daniel Costinett; Zheyu Zhang; Ben Guo; Bo Liu; Ren Ren
    2015 IEEE Energy Conversion Congress and Exposition (ECCE)
    2015

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    GaN heterojunction field-effect transistors (HFETs) in the 600-V class are relatively new in commercial power electronics. The GaN Systems GS66508 is the first commercially available 650-V enhancement-mode device. Static and dynamic testing has been performed across the full current, voltage, and temperature range to enable GaN-based converter design using this new device. A curve tracer was used to measure R<sub>ds-on</sub> across the full operating temperature range, as well as the self-commutated reverse conduction (i.e. diode-like) behavior. Other static parameters such as transconductance and gate current were also measured. A double pulse test setup was constructed and used to measure switching loss and time at the fastest achievable switching speed, and the subsequent over-voltages due to the fast switching were characterized. Based on these results and analysis, an accurate loss model has been developed for the GS66508 to allow for GaN-based converter design and comparison with other commercially available devices in the 600-V class.

  • Zheyu Zhang; Fred Wang; Daniel J. Costinett; Leon M. Tolbert; Benjamin J. Blalock; Haifeng Lu
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    Dead-time in the voltage source converter significantly affects the reliability, power quality and losses. For SiC devices, considering the high sensitivity of turn-off time to the operating conditions (> 5× difference between light load and full load), as well as large extra energy loss induced by reverse conduction during superfluous dead-time (~ 15% of the switching loss), traditional fixed dead-time setting becomes inappropriate. This paper introduces an approach to achieve optimum dead-time for SiC based voltage source converter. First, turn-off behaviors under various operating conditions are investigated, and the relation between optimal dead-times and load currents are established. Second, a practical method for adaptive dead-time regulation is proposed, which consists of a dead-time optimization model and two gate assist circuits to sense the voltage commutation time during turn-off transient. Via synthesizing the monitored switching condition together with the preset dead-time optimization model, the micro-controller is able to online adjust the dead-time. Finally, based on a buck converter with 1200-V SiC MOSFETs, the test results show that by means of the proposed method, the power loss decreases by 12% at full load and 18.2% at light load.

  • Zhiqiang Wang; Xiaojie Shi; Leon M. Tolbert; Fei Fred Wang; Zhenxian Liang; Daniel J. Costinett; Benjamin J. Blalock
    2015 IEEE International Workshop on Integrated Power Packaging (IWIPP)
    2015

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    A board-level integrated silicon carbide (SiC) MOSFET power module is developed in this work for high temperature and high power density applications. Specifically, a silicon-on-insulator (SOI) based gate driver is designed, fabricated and tested at different switching frequencies and temperatures. Also, utilizing high temperature packaging technologies, a 1200 V / 100 A SiC MOSFET phase-leg power module is built. The switching performance of the fabricated power module is fully evaluated at different temperatures up to 225 °C. Moreover, a buck converter prototype incorporating the SOI gate driver and SiC power module is built for high temperature continuous operation. The converter is operated within a wide range from 10 kHz to 100 kHz, with its junction temperature monitored by a thermo-sensitive electrical parameter (TSEP). The experimental results demonstrate that the integrated power module is able to operate at a junction temperature greater of 232 °C.

  • Daniel Costinett
    2015 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2015

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    A concise, analytical method for incorporating the effects of zero voltage switching (ZVS) interval dynamics in small-signal discrete-time models of the dual-active bridge (DAB) converter is detailed. The method allows the influence of the resonant transition between tank inductor and switching device output capacitance to be examined. Importantly, the method does not require the inclusion of an additional state to account for these dynamics, which greatly simplifies the resulting models of converter behavior. The calculations are applicable to any alternate topology where ZVS transition behaviors contribute significantly to converter dynamics, as in many high frequency converters. The method is verified through experimental results on a 1 MHz DAB converter.

  • Sheng Zheng; Jingxin Wang; Fei Yang; Fred Wang; Leon M. Tolbert; Daniel J. Costinett
    2015 IEEE Energy Conversion Congress and Exposition (ECCE)
    2015

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    Continuous variable series reactors (CVSRs), as a cost effective alternative to flexible AC transmission system (FACTS) series compensators, have been proposed to continuously vary the line reactance and control the power flow. The development of the power electronics based dc controller (DCC) is essential and unique to meet the need of CVSR in utility transmission grid applications. In addition to supplying the needed dc current to the CVSR dc winding, the DCC has to deal with the interaction from the ac winding. CVSR, together with DCC, will be installed outdoor in a substation, so the operation environment could be extremely harsh. The detailed design and implementation of the DCC are presented, along with simulations demonstrating the close relationship between the load profile of dc winding and converter output impedance. A 1000 A, 20 kW field prototype has been constructed and tested with a 115 kV, 1500 A CVSR to experimentally verify the performance of the whole CVSR system.

  • Francisco J. Azcondo; Regan A. Zane; Dragan Maksimovic; Daniel Costinett
    2014 XI Tecnologias Aplicadas a la Ensenanza de la Electronica (Technologies Applied to Electronics Teaching) (TAEE)
    2014

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    The paper describes the organizational framework and contents of a newly developed course on power electronics for electric drive vehicles. The course is developed and taught synchronously among three universities, with each institution individually managing student registration and assessments, and course administration. The participation of instructors and students from different institutions increases the impact of the course. In addition to the regular classes, followed on campus and remote, the high quality material generated by the instructors is available for the students, including a repository of recorded video lecturers and conferences given by specialist in key topics. Interaction with instructors and among students is promoted using a collaborative on-line tool.

  • Weimin Zhang; Ben Guo; Fan Xu; Yutian Cui; Yu Long; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel J. Costinett
    2014 IEEE Workshop on Wide Bandgap Power Devices and Applications
    2014

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    Wide band gap (WBG) power devices, such as Silicon Carbide (SiC) and Gallium Nitride (GaN) devices, have been innovatively applied in the data center power converters, which are based on the high voltage DC (HVDC) power distribution architecture, to evaluate the potential efficiency improvement. For the front-end AC-DC rectifier, a buck rectifier using SiC devices was implemented. The SiC devices were tested at first to obtain the static and switching characteristics. The number of devices in parallel, the switching frequency and the input/output filters were investigated. A prototype of 7.5 kW, 3 phase 480 VAC input, 400 VDC output front-end rectifier was built and tested. The peak efficiency reaches up to 98.55%, and the full load efficiency is 98.54%. For the intermediate DC-DC bus converter, the impact of the GaN devices on the LLC resonant converter efficiency was evaluated and compared with the Si counterparts. Based on the device loss analysis and the FEA simulation on the transformer winding loss, the GaN devices exhibited the reduced device loss, and also the capabilities to reduce the transformer winding loss. A 300 W, 400 VDC input, 12 VDC output GaN device based DC-DC bus converter was built and tested by 96.3% peak efficiency and 96.1% full load efficiency.

  • Brad Trento; Leon M. Tolbert; Daniel Costinett
    2014 IEEE Energy Conversion Congress and Exposition (ECCE)
    2014

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    This paper describes a grid synchronization technique for single phase systems using only fixed filtering and compensation networks. Compared with other phase locking techniques, the proposed approach has the advantage of requiring no feedback control and a simplistic and predictable design. The paper uses test scenarios and metrics described in IEEE C37-118.1 for testing phasor measurement units (PMUs) to evaluate the performance of the proposed method. The dynamic response of the proposed approach is compared with the second order generalized integrator phase locked loop (SOGI-PLL) and second order generalized integrator frequency locked loop (SOGI-FLL).

  • Zhiqiang Wang; Xiaojie Shi; Leon M. Tolbert; Fred Wang; Zhenxian Liang; Daniel Costinett; Benjamin J. Blalock
    2014 IEEE Energy Conversion Congress and Exposition (ECCE)
    2014

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    This paper presents a board-level integrated silicon carbide (SiC) MOSFET power module for high temperature and high power density applications. 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 thermo-sensitive electrical parameter (TSEP) 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.

  • Zheyu Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel Costinett
    2014 IEEE Energy Conversion Congress and Exposition (ECCE)
    2014

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    Double 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 (IMD) 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/power cable, two more phase-legs for the three-phase PWM inverter as compared to the DPT, and the parasitic capacitive coupling effect between power devices and heat sink. Based on the three-phase PWM inverter with 1200 V SiC MOSFETs, the test results show that the induction motor, especially with a relatively long power cable, will significantly impact the switching performance, leading to switching time increase by a factor of 2, switching loss increase up to 30%, and serious parasitic ringing with 1.5 μs duration as compared to that tested by DPT. 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 induced by 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.

  • Zheyu Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel Costinett
    2014 IEEE Workshop on Wide Bandgap Power Devices and Applications
    2014

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    This paper focuses on understanding the key impacting factors for switching speed of wide bandgap (WBG) devices in a voltage source converter. First, the constraints and challenges of WBG devices during fast switching transients are summarized. Special attention is given to the transient gate-source and drain-source voltages. Second, the impacts of major components in voltage source converter, including gate drivers, parasitics, inductive loads, and cooling systems, on the switching performance of power devices are systematically investigated. The critical parameters for each component are highlighted. Finally, design criteria are suggested to maximize switching speed of WBG devices.

  • Weimin Zhang; Fred Wang; Leon M. Tolbert; Benjamin J. Blalock; Daniel Costinett
    2014 IEEE Energy Conversion Congress and Exposition (ECCE)
    2014

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    Gallium Nitride High Electron Mobility Transistor (GaN HEMT) is an emerging wide band gap power device in recent years. Using a cascoded structure, the GaN HEMT can be combined with a low voltage MOSFET to make the combination behave as a normally-off device. This paper investigates the soft-switching behavior of cascode GaN HEMT in the phase-leg structure. The analysis reveals some internal device behaviors during the soft-switching transition, which are not found in the non-cascode device. Due to the internal feedback of the cascode structure, the channel current of the internal GaN HEMT drops to zero quickly, leading to extremely low turn-off loss. However, it has been found that there are switching energy loss dissipated in the internal GaN HEMT during the turn-on transient, although the external waveforms of the cascode GaN HEMT exhibit zero voltage switching. The fundamental reason is that ratio of the sum of MOSFET output capacitance and internal GaN HEMT input capacitance to the internal GaN HEMT output capacitance is quite low. Based on the simulation, by adding additional capacitance on the gate source terminals of internal GaN HEMT, these losses can be mitigated. Experimental tests using a commercially available GaN device are presented which show nearly 400 mW of loss at 1 MHz switching frequency in four different load current conditions.

  • Daniel Costinett; Kelly Hathaway; Muneeb Ur Rehman; Michael Evzelman; Regan Zane; Yoash Levron; Dragan Maksimovic
    2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014
    2014

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    Electric-drive vehicles, including hybrid (HEV), plug-in hybrid (PHEV) and electric vehicles (EV), 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 communications 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 low-voltage, low-power dual active bridge (DAB) power converters serving as bypass converter modules. Experimental results are presented for a system consisting of two series 3.6 Ah NMC battery cells and two DAB bypass converters, with combined outputs rated to supply a 12 V, 35 W auxiliary load.

  • Daniel Costinett; Regan Zane; Dragan Maksimovic
    2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014
    2014

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    The small-signal modeling of dual active bridge (DAB) converter dynamics in discrete time is a useful analysis tool due to the ability to incorporate behavior during zero-voltage switching (ZVS) intervals explicitly, and is advantageous for the direct design of digital compensators. While the control-to-output transfer function has been modeled previously, accurate models of the output impedance of the DAB converter which account for the converter behavior during switching intervals have not been proposed. A discrete time model of the DAB output impedance is developed and tested against experimental results for a 1 MHz, 50-to-4 V, 10 W DAB converter. The model is then extended to the analysis of load current step changes asynchronous to the discrete time sampling instances.

  • Daniel Costinett; Daniel Seltzer; Dragan Maksimovic; Regan Zane
    2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference and Exposition (APEC)
    2013

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    Small mismatches in inductor-applied volt-seconds may arise in power converters due to asymmetries in circuit parasitics or modulation waveforms. These small mismatches can have significant impact on circuit operation, including the saturation of magnetic components, loss of regulation, and decrease in converter efficiency. Various auxiliary circuits and control methods have been developed to prevent volt-second imbalances from being applied to magnetic components. In this work, an inherent feedback specific to Zero-Voltage Switched (ZVS) converters is examined which automatically compensates for volt-second mismatch. A closed-form linearized relation between volt-second mismatch and inductor current offset is derived. This relation is then verified through simulation and experimental results using two prototype circuits comprised of an inductively loaded full-bridge and a dual active bridge (DAB) converter.

  • Daniel Costinett; Dragan Maksimovic; Regan Zane; Alberto Rodríguez; Aitor Vázquez
    2013 IEEE 14th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2013

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    The nature of reverse recovery losses is examined in hard-switched and soft-switched converters, using silicon (Si), silicon carbide (SiC), or gallium nitride (GaN) devices. A loss model and experimental results with a prototype 150-to-400 V, 150 W, boost converter operated at switching frequencies between 500 kHz and 2 MHz are used to characterize and quantify losses related to diode reverse recovery. It is found that reverse-recovery related losses with Si diodes cannot be neglected even when the converter is soft switched, with zero-current switching of the diode and zero-voltage switching of the transistor. The switching losses with SiC or GaN diodes are substantially smaller in all cases considered, and can be reduced to negligible values when the converter is soft switching.

  • Daniel Costinett; Miguel Rodriguez; Dragan Maksimović
    2012 15th International Power Electronics and Motion Control Conference (EPE/PEMC)
    2012

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    This paper describes a very simple Digital Pulse Width Modulator (DPWM), with under 100 picoseconds resolution capability in low-cost field-programmable gate arrays (FPGA). The DPWM implementation is based on internal carry chains and internal 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 on specialized phase locked loop or clock management resources. The DPWM is capable of supporting high switching frequencies for digitally controlled switched-mode power converters. A 50 MHz switching frequency DPWM with 60 picoseconds resolution and a 1 MHz switching frequency DPWM with 90 picoseconds resolution are experimentally demonstrated, with monotonicity and excellent linearity.

  • Daniel Costinett; Regan Zane; Dragan Maksimović
    2012 IEEE 13th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2012

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    The existence of parasitic capacitances surrounding switching devices has been well established in the field. These capacitances are capable of having significant impact on the analysis, design, and performance of switched mode power supplies through increased switching loss or altered converter dynamics in the soft-switched case. As power converters continue to move to higher frequency, these effects become more pronounced and must be taken into account in converter design and analysis. 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 developed linear equivalents are then used with traditional circuit analysis to experimentally confirm their ability to accurately model converter operation of an example converter which exhibits significant loss and dynamic effects from device capacitances.

  • Miguel Rodríguez; Greg Stahl; Daniel Costinett; Dragan Maksimović
    2012 IEEE 13th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2012

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    High switching frequencies can lead to converters with reduced size and high power density. Using RF/microwave devices, microwave design techniques can be applied to allow soft-switching of devices and thus high efficiency operation, at the cost of higher complexity and component count. This paper explores the use of microwave GaN High Electron Mobility Transistors (HEMT) to realize power conversion in the 10-100 MHz range using conventional PWM techniques that may enable simple, small and efficient converters. Several driver and test circuits are described, simulated and tested, and experimental results are also provided for a floating buck converter operating at 20 MHz and controlled using conventional PWM techniques.

  • Daniel Costinett; Regan Zane; Dragan Maksimović
    2012 IEEE 13th Workshop on Control and Modeling for Power Electronics (COMPEL)
    2012

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    A discrete-time, small-signal model is developed for the dual active bridge (DAB) converter which considers the effects of zero-voltage switching (ZVS) intervals on converter dynamics. The model is applied to the converter operating under phase-shift modulation, and is shown to be valid across a full range of load values constituting multiple operating modes of the converter. Finally, the model is applied to the case of an unregulated converter to show that output voltage variation that results in improved efficiency over wide range of loads can also lead to simplified control and compensation requirements across the full load range.

  • Daniel Costinett; Regan Zane; Dragan Maksimovic
    2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC)
    2012

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    A control scheme is developed in which efficiency is optimized over a wide range of loads for a Dual Active Bridge (DAB) converter. A simple control strategy is proposed to adjust both the converter conversion ratio and switching dead times 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 W and 120 W.

  • Daniel Costinett; Hien Nguyen; Regan Zane; Dragan Maksimovic
    2011 Twenty-Sixth Annual IEEE Applied Power Electronics Conference and Exposition (APEC)
    2011

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    This paper describes a high step-down unregulated, fixed-ratio DC-DC converter (DCX) based on the dual active bridge (DAB) power stage operating at high switching frequency using enhancement-mode Gallium-Nitride-on-Silicon (GaN) transistors. The DAB power stage design as well as a comparison of losses using GaN and silicon MOS devices is based on a detailed state-plane analysis of resonant transitions. Experimental results are presented for a 150 W, 150-to-12 V prototype DCX operating at 1 MHz switching frequency.

  • Daniel Costinett; Erez Falkenstein; Regan Zane; Zoya Popovic
    The 40th European Microwave Conference
    2010

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    This paper discusses a low-power 2.4GHz ISM band wireless sensor based on commercial components for sensing and data transmission. The sensor is powered wirelessly in the 5.8-GHz ISM band through an integrated 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 use of a low-power microcontroller and a custom power management circuit. In sleep mode, the circuit consumes 1μA at 2.5V.