By Application Area
Electric Vehicles and Aerospace
- SiC-Based Reconfigurable DC-DC Converter Design for Electric Vehicles (EV) Charging and Powertrain Application.arrow_drop_down
The objective of the research is to develop and optimize an integrated converter prototype for 50 kW traction operation as boost converter and 6.6 kW charging operation as dual active bridge (DAB) converter. A scaled down prototype is first developed to verify the reconfigurable integrated converter operation and loss verification. The boost converter is operated in current interleaving mode to reduce the capacitor requirement. Phase shift modulation is adopted for DAB converter. The unique aspect of the design is to incorporate a hybrid high frequency integrated magnetics which can be operated as DC boost inductor and AC isolation transformer for dual active bridge converter. The magnetizing inductance of the hybrid high frequency integrated transformer is used for boost operation and the leakage inductance is used for the DAB converter operation. A model for finite element analysis (FEA) is developed to evaluate the leakage and magnetizing inductance for different winding and core configurations. Based on the leakage and magnetizing inductance, an analytical converter model is developed to predict the transformer current waveforms and output power. To achieve the highest efficiency for different operating conditions, a loss model is developed for efficiency optimization.
Due to the bidirectional power flow capability of DAB converter, it can be operated in both charging operation and traction operation. Since the integrated converter can drive the traction motor as both boost and DAB mode, they are designed independently for highest efficiency at light load and full load condition. For most integrated converter topologies presented in literature, extra mechanical or solid-state contactor is required for reconfiguration which adds cost and increases the volume of the converter. In the proposed integrated converter, reconfiguration between DAB and boost mode is achieved by switching the BMS contactors which are already available in EVs. However, the time required to reconfigure the converter between boost and DAB modes are high due to the mechanical contactors. A trapezoidal modulation scheme is developed to ensure seamless power flow during the mechanical contactor transition time. The modulation scheme ensures the reliability of the BMS contactor and prevents overshoots. Using targeted design approach based on consumer driving habits and drive cycle statistics, the topology provides a unique way to design and optimize independently EV efficiency for different torque-speed requirement.
- Saeed Anwar
The understanding and modeling of switching transient is crucial here. At the core of this problem is the nonlinear and high-order nature of power semiconductor switching behavior. Significant amount of work is spent into identification of components defining switching characteristics and verification of a simulation model. Furthermore, elaborate the switching behavior testing under different working condition and circuit parameters is done to further determine their contribution and prove the knowledge we gained from modeling. Based on these fundamentals, the design and operation of WBG based power converter can be scientifically optimized.
Overvoltage is the ringing spikes exerted on semiconductor during switching transients and the device voltage rating is usually limited by the maximum magnitude. While an empirical percentage value is usually used for the selection of silicon counterparts, the design guideline proposed here help using the most out of the device reliably.
Dead-time is usually inserted between the switching actions of the switching pair to avoid shorting the dc bus voltage to ground and often it is a fixed operation parameter. With the knowledge of current commutation inside the switching pair, we are able to optimize and adaptively tune this parameter by monitoring the switching time. Therefore, operation safety is guaranteed while reducing the diode conduction loss at the same time.
- Intelligent Gate Drive for Maximizing Performance and Enhancing Reliability of Wide Bandgap Semiconductorsarrow_drop_down
This project focuses on the development of an intelligent gate drive (IGD) by means of multiple gate assist units to accommodate the unique characteristics of WBG power semiconductors. The proposed IGD will feature: a) smart driving strategy to achieve fast switching, and minimized voltage spike and parasitic ringing simultaneously; b) cross-talk suppression; c) fast response short-circuit protection; d) online junction temperature monitoring; and e) online switching time detection. The proposed IGD will help to fully realize the benefits of WBG devices in a converter, while minimizing their negative impact on design and operation complexity and reliability.
- Ultra-light Highly Efficient MW-Class Cryogenically Cooled Inverter for All Future Electric Aircraft Applicationsarrow_drop_down
The goal of this project is to build a 1-MW cryogenically cooled inverter with 99.3% efficiency at half power and 26 kW/kg specific power. The main technical barriers include highly-efficient power conversion stage and ultra-light EMI filter for MW-level high frequency cryogenically-cooled power conversion system. These challenges enable the following research opportunities, including but not limited to driving, protection, and characterization of power semiconductor at low temperature, characterization of passives at low temperature, topology, control, and PWM algorithm, advanced EMI filter strategy, cryogenic cooling system, packaging and integration. Also, additive manufacturing is employed to further improve the performance and reduce the weight of the power conversion system.
- WBG-based Power Module for EV Traction Drivesarrow_drop_down
The first step would be to continue design and evaluation on the Gate Driver IC developed previously in order to integrate as many board level circuits into the IC as possible. The second step is to continue design and testing of the isolated power supply IC. The third step is the continuation of switching transient overvoltage modeling. The fourth step is the development of the junction temperature monitoring for SiC based power converters. This fourth step provides for a lifetime enhancement and better reliability of the power converter. The fifth step is the integration of the work done on the previous steps.
- Application of Hybrid Switches (GaN + Si) to the >97%-efficiency 7.2kW Level-2 Chargerarrow_drop_down
This project investigates the impact of parasitics when paralleling GaN to Si, particularly on the gate-drive performance, quantifies the crosstalking between Si and GaN gate drivers, and enhances the thermal performance of such module by paralleling Si MOSFETs, and analyzes the economic impact of adopting such hybrid power module in EV chargers. ANSYS is used to optimize the PCB layout, LTSpice is used to simulate the transient in the driver and switching modules, and the physical charger is built to experimentally validate its effectiveness.
- Liyan Zhu
The charger input is a three-phase boost type PFC. The DC/DC stage uses dual active bridges, adopting single-phase-shift control at the heavy load and dual-phase-shift control at the light load to secure soft switching on. Si MOSFETs from various vendors are compared, in terms of the electrical performance and the cost impact
- Yang Huang
- Liyan Zhu
- Coil Design for Wireless EV Charging arrow_drop_down
Among many WPT coil structures, the series SR coil has been studied carefully for its many superiority over others. Instead of using Litz wire for inductor winding and lumped capacitor as compensated resonant component, SR coil consists of planar inductors made of copper foil. No Litz wire is needed and SR coil can utilize its parasitic capacitance as the compensation network. The total volume of passive component could shrink largely comparing with conventional coil at a given power rating.
Nevertheless, AC copper loss dominates the total ESR, diminishing the performance of SR coil especially at high operating frequency. Moreover, the specific designed capacitance value requires a certain amount of copper area provided by the planar inductor trace, limiting any method to cut down the copper loss. Aiming at increasing the copper area with the given capacitance value constraint, a multi-layer non-uniform SR coil structure has been proposed. Multiple layers of planar inductor are stacked up, with dielectric material in between any two adjacent layers. A 100mm radius multi-layer prototype has been fabricated using ceramic-filled PTFE laminate to prove the validity of this concept. The fabricated coil can reach quality factor over 200, which is almost doubled comparing with 2-layer uniform width SR coil. It has been tested with a 6.78MHz high frequency full bridge inverter in the lab and shows constant characteristics as expected.
- Research and Development of An FPGA based Three-phase High-efficiency SiC Inverter for Electric Vehicles arrow_drop_down
This project will connect the evaluation board of Xilinx FPGA with a SiC inverter in CURENT and apply the common-mode reduction control method to the selected FPGA emulation board). Detailed plan includes: building the Matlab/Simulink model for several control algorithms, generating the FPGA code to the emulation board, developing the software and integrating it into existing FPGA SW, and testing the control algorithm on the SiC inverter based PMSM drive set in CURENT. Meanwhile other advanced control algorithms, including multiple-phase motor control, simultaneous multiple motor control, high-frequency harmonic injection sensorless control will be investigated, to maximize the benefits of SiC and FPGA.
- Yang Huang
- Benchmark and Design Multi-functional EV Chargers Using WBG Devices For Magna Internationalsarrow_drop_down
The UTK team will simulate and compare different charger topologies/concepts at 3.3kW, 6.6kW, 22kW and an 'all-in-one' that can do all the power levels. Firstly, the project will focus on investigating different charger topologies from literature, market and novel ideas. Thereafter, different topologies will be compared in terms of cost, efficiency, weight, power density, etc. and then few of them will be selected for simulation at 3.3kW, 6.6kW, 22kW and 'all-in-one charger'. Finally, based on simulations, an optimal charger design will be suggested at each power level. The target specs include:
- Power Factor at rated power: > 0.99
- Grid-side Current THD < 5%
- Efficiency estimate: >95%
- Output current ripple: <5%
- Operating temperature range: -20~110oC
- Operating voltage range: 80~260V for single phase, 208~480VAC for three phase
- Output voltage range: 200~500VDC
- Rated charging power: 3.3kW~20kW
- Voltage mode / Current mode: Constant Current & Constant Voltage Charging
- No inrush current
- Cooling method: Water cooling
- Bidirectional power flow: plus
- Nick Bianchi
- Daniel Merced Cirino
- Smart, Compact, Efficient 500kW DC Fast Chargerarrow_drop_down
The UTK team will simulate and compare different charging topologies/concepts at MW level, estimate the power loss of the whole charging station, model the magnetics design and build the control strategy using FPGAs.
- Daniel Merced Cirino
- Yang Huang
- Liyan Zhu
Renewable Energy and Energy Storage
- GaN-based Inverter for Photovoltaic Applicationsarrow_drop_down
PV inverters are a hot topic in power electronics research today, focusing on cost and size reduction, efficiency and reliability improvements, and added features like reactive power support. This figure shows a typical single-phase PV inverter architecture, including the transistors (Q1-Q4), gate drivers, and filter. The filter is usually composed of inductors and capacitors, which can make up a large portion of the inverter size and cost. In addition to the components shown here, auxiliary electronics are required to provide regulated voltage levels, control signals, and protection. The transistors and passive components also require a heatsink or cooling system to keep them within their rated operating temperature range.
One way to improve an inverter is to select a new topology, as opposed to the conventional hard-switching full-bridge converter shown here. But even with the same topology, the size and cost of filters can be greatly reduced by increasing the switching frequency of the transistors. However, higher frequency causes higher switching losses, which reduces the inverter efficiency and requires a larger heatsink to keep the transistors from overheating. This tradeoff is at the heart of PV inverter research.
This projects aims to design a lower cost PV inverter using GaN-based power electronics, which maintaining the same capabilities, efficiency, size, and design margins for reliability as in today’s commercially available products. In order to achieve this goal, the key research areas include design of the gate drivers, heatsink, control, and filter, as well as the topology and layout of the inverter.
- Grid Integration of Renewable Energy Sourcesarrow_drop_down
This project develops the power electronics interfaces with renewable energy sources and control strategies needed for active voltage and frequency regulation, as shown in Fig. 1. Using the developed model and control strategies, capabilities of these renewable energy sources with interface converters are investigated, including active and reactive power, voltage, inertia, and impedance characteristics.
The project also develops the stability criterion and design methodology of renewable interface converters to guarantee the stable operation of power systems with high penetration of renewable energy sources, such as a grid-connected radial-line PV system with multiple PV inverters. The harmonic stability of grid-integrated renewable energy systems is analyzed using the impedance-based stability criteria. Based on the stability analysis, the converter controller parameters are designed to ensure the system stability without harmonic resonance problems.
- Wenchao Cao
- Yiwei Ma
- Little Box Challenge Inverterarrow_drop_down
The University of Tennessee (UTK) in partnership with the Electric Power Research Institute (EPRI) previously built a 2 kVA single-phase inverter with ultra-high power density (102 W/in3) using WBG devices. The inverter power stage and overall system size were minimized through a multi-faceted approach. During the design stage of the project, many different approaches were analyzed through complete paper designs to compare total displacement volume. This included alternate energy storage implementations, converter topologies, switching frequencies, and device and passive materials. However, complete in-house static and switching performance characterization of multiple WBG devices, including thermal variations in key parameters, allowed for the miniaturization of the final design.
Building up on the 2kVA single phase inverter previously developed for the contest, we are developing new approaches that can be implemented to further improve the current topology.
- WBG-based 20 kW dc-dc converter for interfacing solar energy with the hardware testbed.arrow_drop_down
Traditional interleaved converters can be further improved by adding other distinctive functionalities and features into its operation, e.g. operating the converter in DCM mode, applying ZVS or ZCS etc. An effort will be made to propose a more improved topology of buck boost interleaved converter which will incorporate innovative features resulting in reduced loss and smooth converter operation.
This high power buck boost type dc-dc converter needs to withstand high voltage (600 V), and high output current (maximum 400 A). To share this high current, N number of parallel stages will be designed. These stages will also be phase shifted to achieve advantages like input and output voltage ripple cancellation, improved load transient response, etc.
As the number of interleaved stages increases, the control complexity increases too. The main challenge of this research would be to implement innovative ideas into the operation and control circuitry of this converter that would led to a very smoothly controlled and efficient converter. Designing proper cooling system would also be crucial issue of this research.
Prior to hardware implementation of this converter, detailed analysis of the converter steady state operation, and mathematical modelling of converter dynamics incorporating losses will be done.
- Manashi Roy
- Mark Nakmali
This research focusses on building a 2 kW residential photovoltaic single-phase string inverter that is reliable, robust, efficient, and low cost. Traditional PV converter topologies are implemented using single-purpose power stages and passives. A conceptual DHA system is implemented with a common set of hardware resources that shift operation between active power filtering (APF: double-line-frequency decoupling) and line frequency inverter operation. A plurality of identical modules comprise the shared hardware resources. According to a dispatch controller, each module in the DHA system is either a bucktype APF (with embedded energy storage) or a zero voltage switching (ZVS) inverter phase leg, in each case controlled through a low frequency current reference. The system uses a dual-current programmed mode (DCPM) to achieve ZVS of all transistor while regulating peak and valley currents in each period. This modulation results in large ripple, particularly at high output current, which is mitigated simply by the multiphase nature of the DHA, allowing reduced EMI filtering. The modular DHA structure also allows ripple energy storage capacitors to be embedded at the module level, breaking the energy storage into smaller and therefore more reliable banks, and allowing the system to be devoid of a single point of failure.
The ongoing research is also looking at optimally sizing the APF energy storage capacitors and the optimal operation of each modules between APF and inverter operation. With separate inverter and APF operation, power stages of each must be sized according to the individual maximum instantaneous power of each. When completed, the proposed research will demonstrate a paradigm-altering approach to power electronics design, applied to PV inverters.
- Kamal Sabi
- High voltage direct current (HVDC) transmissionarrow_drop_down
Two types of HVDC converters are used, the current source converters (CSC) and the voltage source converters (VSC). VSC-HVDC has the advantages of low harmonics, black start capability and independent active and reactive power control, which make it suitable for the growing renewable energy resources integration applications, such as offshore wind farm. The state-of-the-art VSC-HVDC converter topology is the modular multilevel converter (MMC), as shown in the figure. MMC exhibits many advantages, such as no direct series of power switches due to the modular structure with a series connection of power electronics building blocks (i.e. submodules), and high efficiency and low harmonics due to the multilevel structure.
However, MMC requires large submodule capacitors due to the single-phase nature of the submodules and low switching frequency. It also has an inherently uneven power loss distribution between the two devices in the submodule, which may lead to overdesign of the cooling system. These shortcomings of MMC may hinder their applications where size and weight are important, such as for offshore wind.
This project aims to increase the MMC power density, by proposing methods to reduce the capacitor voltage ripples and deal with the uneven power loss distribution in submodules.
- Shuoting Zhang
- Siqi Ji
- Xiaojie Shi
- Yalong Li
The proposed microgrid is expected to improve the energy use efficiency by 20% and reduce the annual critical loads interruption time by 98% from 50 minutes to 1 minute. At the same time, the controller and its deployment cost can be cut by half. The community based microgrid and its controller will help the proliferation of the microgrid technology, which can lead to 1% reduction of the total CO2 emission by electricity generation in US if widely used.
There are two main phases for the project, the design phase and the testing phase. The design phase will focus on the MG design, implementation, and design methodology development, as well as the MG controller development. The testing phase will focus on testing the designed and developed MG and MG controller using multiple simulation and emulation platforms, as well as the controlled field testing. During the testing phase, technology to market activities will be conducted on commercialization of the developed open source low cost MG controller.
The project focuses on the development of a power electronics based dc current controller (DCC) for continuously variable series reactors (CVSRs) to continuously vary the line reactance and control the power flow on the transmission and distribution system. Compared with FACTS series compensation devices, DCC only performs control function, is isolated from the high voltage ac line and can be of much lower voltage and power rating, ultimately reducing the system cost. But a regulated dc current from 0 to 1000 A must be supplied by the DCC under different ac load and dc flux bias conditions, which is a big challenge due to the non-linear characteristic relationship between induced back-emf and dc current. Furthermore, high reliability is critical for acceptance in utility applications. To minimize maintenance, a natural convection cooling system instead of forced air cooling is required and poses additional restrictions for the topology and device selection.
In this research, a new modulation scheme, which can simultaneously generate two different ac frequencies while suppressing undesired harmonics in between, is first proposed and systematically investigated, and then the proposed modulation is verified on a 100 W prototype. Second, the band-pass filters that are employed to separate different frequencies from the inverter are designed and compared to achieve better filtering effect. Next, advanced filter network involving planar transformer design will be conducted to further minimize the system volume as well as to modeling the parasitic effect of filtering network. Finally, the leakage current caused by high order harmonics will be addressed using the proposed modulation scheme, and corresponding modification and tradeoffs will be studied in the stage.
Modulation Scheme Study
Two different modulation schemes, unipolar and bipolar dual-frequency selective harmonic elimination (DFSHE), are investigated. Compared to traditional PWM modulation, which controls only the fundamental frequency of the output waveform through modulation of duty cycle at constant frequency, selective harmonic elimination (SHE) modulation varies both switching frequency and duty cycle per switching period in order to generate an output in which a large range of the output spectrum is directly controlled. The SHE method uses Fourier analysis, based on the desired output spectrum, to synthesize a pulse train, consisting of a number of discrete switching instances. Each switching instance is defined by switching angles relative to the fundamental period. In this work, the SHE method is extended to a dual-frequency scheme. Rather than generating a single fundamental frequency and cancelling n harmonics, the DFSHE approach regulates the amplitude of the fundamental and a kth harmonic to controlled values, while cancelling all harmonics in between and, possibly, a number of harmonics above the kth.
Passive Component Design and Integration
Two band-pass filters (LC resonant tank) are first adopted in the prototype to separate the fundamental and the kth harmonic, while attenuating other frequency element out of their resonant frequencies. The load variation will influence the quality factor of such two-order filters, and therefore, higher order filters are studied and further simulated to compare with the performance of the two-order filters. On the other hand, parasitic capacitance and ac resistance of inductor windings will bring impacts on the tuning of the appropriate frequencies of individual filters. As a result, a compact planar magnetic design will be conducted to precisely model and control such parasitic effect. Also, such component integration will decrease overall volume of the system.
- Chongwen Zhao
- RF Wireless Energy Harvestingarrow_drop_down
The goal of our research is to establish a method for optimizing low power boost converters for use in far-field energy harvesting systems. By using a database of manufacturer-provided device characteristics, we are able to construct Figures of Merit (FOMs) capable of predicting component power loss based on boost converter parameters. A loss model based on a resistor emulation approach shown in  is constructed. Using this loss model, we were able to predict device power losses and system efficiency over a wide range of operating points.
It has been well-established through research that GaN devices have significantly fewer parasitic charges than silicon devices [7,8]. Because switching losses are proportional to both parasitic gate charges and frequency, lower gate charges allow for potential higher frequency operation while maintaining low power loss. One benefit of higher frequency operation is the potential to reduce inductor size while maintaining a constant current ripple. By reducing inductor size, we can increase the power density of the energy harvesting system. The creation of the FOMs allow us to understand the trade-offs which come with higher switching frequency and higher power density.
In order to illustrate the use of this system in a real-world application, we are constructing a system which uses an energy transducer called a rectenna, which transforms RF energy to electrical energy, to charge a battery through an optimized converter. A microcontroller controls the converter operation while monitoring the voltage at the output of the rectenna and the battery voltage. A transceiver then transmits this information to a receiver which displays the information to a user.
- Doug Bouler
- Jared Baxter
- Multi-load Multi-frequency Wireless Power Transferarrow_drop_down
In this research, the dual-frequency selective harmonic elimination (DFSHE) modulation scheme, which can simultaneously generate two different ac frequencies while suppressing undesired harmonics in between, is employed on a GaN-based WPT inverter, and then is verified on a 5 W prototype. Considering the wide difference between the fundamental output and its 67th harmonic, initial guess for numeric iteration algorithm is very critical and thus some investigation and modification are conducted for DFSHE to accommodate its application for WPT. Then, the circuit model of dual-frequency WPT system is studied and assumptions are made to achieve desired performance. In such model, different frequency path should show high impedance other than its own resonant frequency to minimize circulation current. High-order harmonics that out of the control range may lead to voltage pulsation, and some techniques will be investigated to alleviate such issues. In addition, multi-load regulation and operation within the same standard will be accomplished using the proposed modulation scheme. By fully utilizing available frequency band in one standard, individual load could be well regulated and controlled on its own, while only one inverter is involved. The selection of certain frequencies, and resonant network design will be considered and discussed to achieve better regulation performance.
- Chongwen Zhao
The overall goal of this project is to provide new magnetic design parameters for more power efficient inductive components. These design parameters will provide guidelines for the inductor and the corresponding electropermanent magnet. Design variables for creating an energy efficient inductor include core dimensions, number of coil turns, airgap length, operating frequency and saturation levels. Design variables for the electropermanent magnet include, operational characteristics of permanent magnetic materials and their dimensions as well as energy required to alter the state of the electropermanent magnet. The electropermanent magnet-inductor pair design variables include optimal airgap between components for maximal flux cancellation and minimizing electromagnetic interference.
The internal flux of the electropermanent magnet-inductor pair were modeled using magnetic circuits and Finite Element Method Magnetics software. The saturation levels of the inductor were then tested using a custom designed PCB that includes dynamic switching capabilities of the electropermanent magnet. Currently, work is being done to switch the electropermanent magnet dynamically with a 60Hz current sine wave through the inductor. As the sine wave approaches its peak values the electropermanent magnet will switch on to adjust the inductor current so that it remains within its saturation limit.
- Maeve Lawniczak
A single-stage 6.78 MHz transmitter is proposed which directly converts a utility ac input to a regulated, high frequency (6.78 MHz) ac output for wireless power transmission. The topology integrates a totem-pole rectifier operating in discontinuous conduction mode (DCM), and an asymmetrical voltage cancellation (AVC) controlled full bridge inverter. Compared with the traditional cascaded multi-stage transmitters, this single-stage approach achieves high power efficiency over the full load range, utilizes fewer GaN FETs, and shrinks the size of the converter. The operation and theoretical analysis of the single-stage transmitter are verified using a 100 W, GaN-based prototype .
A simple auxiliary circuit is added in the single-stage transmitter to further improve the light load efficiency by at least 5%. When output power is high, heavy load operation mode (with totem-pole rectifier) provides high PF and low THF of the input current. When the output power decreases to a certain value, light load mode (with voltage doubler) replaces heavy load mode to obtain high efficiency. The smooth transition between the two operation modes is achieved via an auxiliary circuit .
Constant transmitter coil current enables fast response to a sudden load change, so it is preferred in the multiple receivers application where frequent load changes are occurring. With the implementation of AVC modulation and impedance matching network in the single-stage transmitter, constant transmitter coil current is achieved over wide load range. Experimental results verify that multiple consumer electronics loads are charged from a single transmitter .
- Ling Jiang
- Automated Device Analysis and Converter Designarrow_drop_down
For this project there are three main subsections that work together to accomplish the end goal. The first is a device database that contains various properties of many of the devices available on the market. This database is what will allow engineers to effectively search through the available devices to find the best device for a given situation. Along with the database a selection algorithm will be employed to search through the available data and find devices that are appropriate for the desired converter. The database has already been partially implemented; however, the selection algorithm is still in the planning stages. The second part of this project is the Automated Double Pulse Test. While there is a large amount of data available through device datasheets, its ability to predict device performance under a wide range of operating conditions is somewhat limited. In order to determine the performance of a device in a variety of situations, the device must undergo physical testing, most importantly, the double pulse test. The double pulse test is a somewhat long procedure and requires a significant time commitment to complete, especially when a fine combination of operating voltages and currents is desired. The Automated Double Pulse Test allows this process to be completely automated, with all desired measurements and calculations preformed automatically. In the future it will also allow for the data to automatically be added to the database. The final part of this project is a generalized test board that ties in closely with the Automated Double Pulse Test. This generalized test board will allow many devices to be tested with only minor changes to the test board and produce comparable results.
- Kyle Goodrick
- Wen Zhang
- Edward Jones
The project aims to develop a next generation of rectifier power supply with 98% peak efficiency and high density based on new wide band gap devices. To achieve this, approaches in several aspects are conducted:
- System architecture: Single-stage architecture consisting of power factor correction (PFC), voltage regulation (VR) and DC-DC converter is designed and implemented.
- Power semiconductor devices: New WBG devices like GaN and SiC MOSFETs are implemented as the primary devices. For the secondary side, LV eGaN FET or silicon MOSFETs are considered to be used. Further, advanced packaging and layout techniques are conducted to improve parasitics and associated switching losses.
- Passive components: Innovative magnetic devices are designed to fully utilize the superior switching performance of WBG devices. Also, the achieved higher switching frequency enables smaller magnetics. Modern magnetic materials such as nanocrystalline cores are used to minimize passive losses and size
- Power quality and EMI filter design: Analyze circuit noise sources and design input filter to meet the conducted EMI, THD and power quality requirements. Also, the filter loss and thermal performance will be measured and optimized.
A rectifier is used to transform the AC signal of the WPT receiver coil into a DC signal in the device under charge. Essentially, the rectification stage enables the magnetic field (supplied by the transmitter) to be used to charge a battery in a mobile device. In this research, a synchronous rectifier is chosen and designed to use gallium nitride (GaN) switches and an inductor and capacitor (resonant tank), each in parallel with the rectifier's input. The resonant tank enables zero voltage switching (ZVS) in order to lower the power loss and raise power transfer efficiency.
For 6.78 MHz WPT systems, electromagnetic radiation is a potential problem. Generally, a multistage filter is used to remove harmonic distortion within the circuit waveforms. However, a better technique is to avoid creating harmonic distortion in the first place, and the solution presented in this research utilizes the resonant tank to elongate the ZVS transitions, thereby reducing the harmonic distortion generated by the circuit. Because the rectifier is actively switching, it is also possible to control the equivalent input phase of the rectifier. This is very useful in WPT charging (especially for multi-load WPT) because it allows the receiver to customize its load for optimizing the overall system efficiency. Overall, the rectifier researched here is a comprehensive solution that addresses many challenges for 6.78 MHz WPT systems, and eventually, makes WPT a little more intuitive for the end user.
- Spencer Cochran