@article{zhu_wang_huang_booth_zhang_2019, title={7.2-kV Single-Stage Solid-State Transformer Based on the Current-Fed Series Resonant Converter and 15-kV SiC MOSFETs}, volume={34}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2018.2829174}, abstractNote={This paper proposes a novel two-level single-stage direct ac–ac converter for realizing a 7.2-kV medium-voltage (MV) solid-state transformer (SST) based on 15-kV SiC mosfets. A new current-fed series resonant converter (CFSRC) topology is proposed to address major challenges in MV ac–ac converters such as achieving zero-voltage switching (ZVS) for the MV mosfets across wide voltage and load ranges and minimizing system capacitance. The topology is analyzed with both time-domain analysis and first harmonic approximation to provide useful equations for circuit design. Constant deadtime strategy is adopted, allowing partial ZVS to occur at low-voltage (LV) levels. ZVS behavior over wide voltage range is investigated, and calculation of the associated loss from partial ZVS is presented. System parameters are optimized based on the tradeoff between conduction loss and switching loss. The 15-kV mosfet has been tested continuously at a park voltage of 10 kV and 37 kHz, indicating stable device operation and an extremely high voltage × frequency figure of merit. Moreover, inherent cycle-by-cycle current limiting in the proposed CFSRC under output short-circuit circumstance is realized by paralleling diodes to the LV resonant capacitors. Without employing any additional current sensors, the input and circulating currents are limited to a safe range automatically when the short-circuit occurs. This paper presents detailed short-circuit protection operating principles and peak resonant current equation to aid the design of the resonant tank. A full-scale and compact SST that converts 7.2 kV ac to 240 V ac is developed to verify the theoretical analysis. This is the highest reported voltage rating for two-level-based power converters without device series connection. ZVS is verified and achieved over wide voltage and load ranges with a peak efficiency of 97.8%. A short-circuit experiment is conducted at 3-kV peak voltage to verify the analysis. Experimental results closely match the theoretical analysis.}, number={2}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Zhu, Qianlai and Wang, Li and Huang, Alex Q. and Booth, Kristen and Zhang, Liqi}, year={2019}, month={Feb}, pages={1099–1112} }
 @article{wang_zhu_yu_huang_2017, title={A Medium-Voltage Medium-Frequency Isolated DC-DC Converter Based on 15-kV SiC MOSFETs}, volume={5}, ISSN={["2168-6777"]}, DOI={10.1109/jestpe.2016.2639381}, abstractNote={In this paper, a novel isolated dc–dc converter topology for medium-voltage (MV) applications is proposed by combining the advantages of resonant converters and dual active bridge (DAB) converters. In normal load scenario, this converter operates in an open loop resonant mode with a fixed switching frequency equals to the resonant frequency of the series resonant tank. Thus, zero voltage turn on at primary side and zero current turn off at secondary side are secured from zero to full load. When overload happens, the resonant capacitors will be clamped to the output voltage by the additional paralleled diodes. The proposed converter automatically switches to resonant and DAB mixed operation mode; therefore, the resonant current is naturedly limited. With zero to full load range soft switching and fast overload protection, the proposed topology is especially suitable for MV medium frequency applications utilizing high-voltage SiC MOSFETs. The converter operation modes are analyzed using time-domain waveforms and graphical state trajectory to derive the quantitative relationship between duty cycle, output voltage, and the overload current. Based on these relationships, a predictive duty cycle control is proposed to further limit the overload current of the resonant tank by sensing the output voltage. Combing the proposed topology and the predictive control, cycle-by-cycle overload and short-circuit protections are achieved. To fully utilize the capability of the 15-kV SiC MOSFET, magnetizing inductance, dead time, MV transformer, and resonant components are optimized with the operating range of 6–12 kV and 20–100 kHz. An experimental prototype running at 6 kV and 40 kHz is successfully tested with peak efficiency exceeding 98%. Test waveforms at no load and 10-kW full load validate the zero to full load range soft switching capability. Short circuit protection test demonstrates a 25- $\mu \text{s}$  overload protection speed.}, number={1}, journal={IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS}, author={Wang, Li and Zhu, Qianlai and Yu, Wensong and Huang, Alex Q.}, year={2017}, month={Mar}, pages={100–109} }
 @inproceedings{wang_zhu_yu_huang_2016, title={A study of dynamic high voltage output charge measurement for 15 kV SiC MOSFET}, DOI={10.1109/ecce.2016.7854789}, abstractNote={Newly developed 15 kV silicon carbide (SiC) power MOSFETs with fast switching capability enable the reduction of size, weight and complexity of medium voltage power converters. In medium voltage and high frequency applications, zero voltage switching (ZVS) is necessary since significant amount of energy is stored in MOSFETs' parasitic output capacitors. Recovering these energy is important for high conversion efficiency while ZVS also reduces the dV/dt significantly in these devices. To guarantee complete ZVS, it is crucial to accurately characterize the output charge of devices. In this paper, existing high voltage capacitance and output charge measurement techniques are reviewed. A dynamic half-bridge test method for 15kV SiC MOSFETs' output charge measurement is thoroughly analyzed and experimentally verified up to 6 kV. Output capacitance model is then derived using the measured results. The test circuit not only reflects the realistic ZVS scenario, but also achieves high accuracy (<1% error) without resorting to special equipment or complex configuration which are usually necessary in high voltage test. System level design consideration, error analysis and accuracy certification for this high voltage tester is also given in the paper.}, booktitle={2016 ieee energy conversion congress and exposition (ecce)}, author={Wang, L. and Zhu, Q. L. and Yu, Wensong and Huang, A. Q.}, year={2016} }
 @inproceedings{zhu_wang_zhang_yu_huang_2016, title={Improved medium voltage AC-DC rectifier based on 10kV SiC MOSFET for solid state transformer (SST) application}, DOI={10.1109/apec.2016.7468196}, abstractNote={An improved bidirectional medium voltage AC-DC converter based on 10kV silicon carbide (SiC) MOSFETs for SST (Solid State Transformer) application is presented in this paper. Avalanche breakdown of the reverse blocking silicon diode and bridge arm shoot-through problems in traditional high voltage bridge-type AC-DC converters are solved. Shoot-through currents are limited to low di/dt events that are readily controlled, allowing zero dead-time operation. The reverse recovery dissipation of the SiC MOSFET is eliminated because no freewheeling current will flow through the body diode. This increases the efficiency as well as the reliability of the SiC MOSFET. Detailed power stage operating principles and energy transfer mechanism are described. A unique customized 10kV SiC MOSFET/JBS diode power module is developed and tested, which further reduces parasitic parameters and simplifies converter wire connection. This topology is therefore a very good choice for median voltage applications.}, booktitle={Apec 2016 31st annual ieee applied power electronics conference and exposition}, author={Zhu, Q. L. and Wang, L. and Zhang, L. Q. and Yu, Wensong and Huang, A. Q.}, year={2016}, pages={2365–2369} }
 @inproceedings{huang_wang_tian_zhu_chen_yu_2016, title={Medium voltage solid state transformers based on 15 kV SiC MOSFET and JBS diode}, DOI={10.1109/iecon.2016.7793121}, abstractNote={This paper discusses the advancements in the development of the medium voltage solid state transformer (SST) based on 15 kV SiC MOSFET and JBS diode. Designed for 7.2 kV single phase distribution grid applications, the medium voltage SST converts high voltage AC to low voltage 240/120V ac. The use of ultra-high voltage SiC devices allows the simplification of the power conversion circuit topology. This paper presents the characteristics of the high voltage SiC MOSFET devices as well as the topology innovations to achieve ultra-efficient SST design. Specifically, three different designs are discussed which utilize three-stage, two-stage and single stage power conversion topologies to achieve the AC to AC conversion.}, booktitle={Proceedings of the iecon 2016 - 42nd annual conference of the ieee industrial electronics society}, author={Huang, A. Q. and Wang, L. and Tian, Q. and Zhu, Q. L. and Chen, D. and Yu, Wensong}, year={2016}, pages={6996–7003} }
 @inproceedings{zhu_wang_zhang_yu_huang_ni_2016, title={Practical consideration and implementation of a medium voltage SiC AC-DC rectifier}, DOI={10.1109/ecce.2016.7855240}, abstractNote={The implementation of a novel bidirectional medium voltage AC-DC converter based on 10kV SiC MOSFET is presented in this paper. The improved topology allows the removal of the reverse blocking silicon diode in medium voltage SiC MOSFET module. Shoot-through problems and avalanche of the integrated silicon diode in traditional medium voltage bridge-type AC-DC converters are solved, allowing zero dead-time operation with no current flowing through the body diode. The number of parasitic capacitors at each swing point are reduced by half, greatly reducing the dominant turn on losses caused by these capacitors. A unique customized four-in-one 10kV SiC MOSFET/JBS diode power module with high voltage isolation capability is developed and tested, which reduces parasitic parameters and simplifies converter complexity. Section based winding method is further used to reduce the inductor parasitic capacitance by 40%, helping to reduce the dominant turn-on losses by 13%. Anti-windup and feed forward control are implemented to achieve better performance. Soft start combining with a high voltage relay and fuse are used to limit the inrush current and overshoot voltage during the start-up process. Delta-sigma based fiber optical high voltage sensor is designed and implemented to achieve higher than 10kV voltage sensing capability.}, booktitle={2016 ieee energy conversion congress and exposition (ecce)}, author={Zhu, Q. L. and Wang, L. and Zhang, L. Q. and Yu, Wensong and Huang, A. Q. and Ni, X. J.}, year={2016} }
 @inproceedings{wang_zhu_yu_huang_2015, title={A medium voltage bidirectional DC-DC converter combining resonant and dual active bridge converters}, DOI={10.1109/apec.2015.7104486}, abstractNote={In this paper, an isolated bidirectional dc-dc converter for medium voltage application is proposed. It combines the resonant converter and dual active bridge converter (DAB). Under normal load condition, this isolated converter operates at resonant point to achieve zero voltage (ZVS) turn on at primary side and zero current (ZCS) turn off at secondary side. When over current happens, the voltage across the resonant capacitor will be clamped by paralleled diode and the converter will automatically switch to resonant and DAB mixed operation mode, therefore cycle-by-cycle over current protection is achieved with constant switching frequency. Different operation modes are analyzed for the proposed circuits using time domain waveform and state trajectory. Detailed theoretical analysis and design procedure for transformer, resonant tank and semiconductor devices are discussed. Performance of the proposed circuit is verified by a 3 kV to 200 V, 2.5 kW experimental prototype with high voltage SiC devices.}, booktitle={2015 thirtieth annual ieee applied power electronics conference and exposition (apec 2015)}, author={Wang, L. and Zhu, Q. L. and Yu, Wensong and Huang, A. Q.}, year={2015}, pages={1104–1111} }
 @inproceedings{zong_zhu_yu_huang_2015, title={Auxiliary power supply for solid state transformer with ultra high voltage capacitive driving}, DOI={10.1109/apec.2015.7104472}, abstractNote={This paper proposes an auxiliary power supply (APS) for solid state transformers (SST), which is able to handle extremely high input voltage. Input series output parallel (ISOP) structure is used and only one controller IC is adopted to regulate the output voltage, which simplifies the structure and reduces the cost effectively. Capacitive driving is used to drive multiple switches in different modules of the APS. The proposed capacitive driving method is able to transfer gate signal and driving energy simultaneously even for thousands of volts, which largely reduces the cost and size of the APS. Finally the proposed auxiliary power supply is verified and demonstrated through a 12W prototype.}, booktitle={2015 thirtieth annual ieee applied power electronics conference and exposition (apec 2015)}, author={Zong, S. and Zhu, Q. L. and Yu, Wensong and Huang, A. Q.}, year={2015}, pages={1008–1013} }