@inproceedings{song_huang_zhang_liu_ni_2016, title={15kV/40A FREEDM super-cascode: A cost effective SiC high voltage and high frequency power switch}, DOI={10.1109/ecce.2016.7854643}, abstractNote={High voltage wide bandgap (WBG) semiconductor devices like the 15kV SiC MOSFET have attracted great attentions because of its potential applications in high voltage and high frequency power converters. However, these devices are not commercially available at the moment and their high cost due to expensive material growth and fabrication may limit their widespread adoption in the future. In this paper, a 15kV/40A three terminal power switch, the FREEDM Super-Cascode, is reported for the first time which is based on series connection of 1.2kV SiC power devices. The design and operation principle of the FREEDM Super-Cascode are introduced and the performance including the static blocking capability, conduction characteristics over a wide range of temperatures, and dynamic switching performances are analyzed. In addition, the thermal resistance of the FREEDM Super-Cascode is measured and the power dissipation capability is projected. The FREEDM Super-Cascode costs only one third of the estimated high voltage SiC MOSFETs, and will facilitate early applications of SiC in very high voltage and high frequency power converters.}, booktitle={2016 ieee energy conversion congress and exposition (ecce)}, author={Song, X. Q. and Huang, A. Q. and Zhang, L. Q. and Liu, P. K. and Ni, X. J.}, year={2016} }
 @inproceedings{tan_liu_ni_peng_song_huang_2016, title={Performance evaluation of multiple Si and SiC solid state devices for circuit breaker application in 380VDC delivery system}, DOI={10.1109/apec.2016.7467990}, abstractNote={The DC power delivery system is becoming an appealing research topic and real world solution due to its higher energy efficiency compare with AC delivery system. It has already been applied in data centers, commercial buildings, electrical vehicle charge stations and micro grid systems, etc. Among many new issues that need to be addressed for the DC power delivery system, ultra-fast and accurate protection is one of them. The 1200V SiC devices has been developed by many manufacturers in recent years which makes them good candidates in DC circuit breaker application. In this paper, the 380V DC circuit breaker employing solid state devices for DC power delivery system has been proposed and introduced. The criteria of device characteristics particularly for DC solid state circuit breaker application is discussed and defined. Characteristics of 4 different Si and SiC solid state devices in similar power rating have been compared based on defined criteria. The pros and cons of different devices candidates is introduced with test results for DC circuit breaker application.}, booktitle={Apec 2016 31st annual ieee applied power electronics conference and exposition}, author={Tan, K. and Liu, P. K. and Ni, X. J. and Peng, C. and Song, X. Q. and Huang, A. Q.}, year={2016}, pages={983–989} }
 @inproceedings{chen_yu_ni_huang_2015, title={A new modulation technique to reduce leakage current without compromising modulation index in PV systems}, DOI={10.1109/ecce.2015.7309724}, abstractNote={The transformerless grid-connected PV system suffers from leakage current and neutral voltage imbalance if three-level inverters are utilized. This paper first investigates the common-mode voltage (CM voltage) reduction/elimination methods in three-phase PV inverters, especially three-level inverters. Several mainstream common-mode voltage reduction/elimination methods, including AZSPWM, 2MV1Z, 3MV, 3MV120, are compared in terms of CM voltage reduction/elimination performance, switching losses, modulation index, linear region and neutral point voltage balancing ability. Then a new topology and modulation scheme are proposed, which reduce the frequency of the CM voltage to the order of line frequency and could reach a 100% modulation index. This method is discussed in detail and is verified by simulation.}, booktitle={2015 ieee energy conversion congress and exposition (ecce)}, author={Chen, Z. P. and Yu, Wensong and Ni, X. J. and Huang, A.}, year={2015}, pages={460–465} }
 @inproceedings{song_huang_ni_zhang_2015, title={Comparative evaluation of 6kV Si and SiC power devices for medium voltage power flectronics applications}, DOI={10.1109/wipda.2015.7369289}, abstractNote={In order to better assist researchers to select the appropriate power device for medium voltage power electronics applications, this paper presents a comparative evaluation on three typical 6kV level Si and SiC power devices, including 6.5kV/25A Si IGBT from ABB, 6.5kV/15A normally off SiC JFET from USCi and a FREEDM System Center developed 6kV/26A SiC series-connected JFET. The 6.5kV Si IGBT and 6.5kV SiC JFET are packaged in the same module to minimize the effect of different parasitic inductance on the comparison. The 6kV SiC series-connected JFET is developed based on one 1.2kV SiC MOSFET from Cree and four 1.2kV SiC JFETs from Infineon, in this paper, named FREEDM Super-Cascode. A short introduction on the three selected devices are first given, then their forward conduction and switching performances are compared. Also, some additional features are discussed and compared, including the device size, cost, gate driver circuit complexity.}, booktitle={WiPDA 2015 3rd IEEE Workshop on Wide Bandgap Power Devices and Applications}, author={Song, X. Q. and Huang, A. Q. and Ni, X. J. and Zhang, L. Q.}, year={2015}, pages={160–165} }
 @inproceedings{ni_gao_song_huang_yu_2015, title={Development of 6kV SiC hybrid power switch based on 1200V SiC JFET and MOSFET}, DOI={10.1109/ecce.2015.7310240}, abstractNote={Series-connected power switch provides a viable solution to implement high voltage and high frequency converters. By using the commercially available 1200V Silicon Carbide (SiC) Junction Field Effect Transistor (JFET) and Metal Oxide semiconductor Filed-effect Transistor (MOSFET), a 6 kV SiC hybrid power switch concept and its application are demonstrated. To solve the parameter deviation issue in the series device structure, an optimized voltage control method is introduced, which can guarantee the equal voltage sharing under both static and dynamic state. Without Zener diode arrays, this strategy can significantly reduce the turn-off switching loss. Moreover, this hybrid MOSFET-JFETs concept is also presented to suppress the silicon MOSFET parasitic capacitance effect. In addition, the positive gate drive voltage greatly accelerates turn-on speed and decreases the switching loss. Compared with the conventional super-JFETs, the proposed scheme is suitable for series-connected device, and can achieve better performance. The effectiveness of this method is validated by simulations and experiments, and promising results are obtained.}, booktitle={2015 ieee energy conversion congress and exposition (ecce)}, author={Ni, X. J. and Gao, R. and Song, X. Q. and Huang, A. Q. and Yu, Wensong}, year={2015}, pages={4113–4118} }
 @inproceedings{wang_huang_wang_song_ni_ryu_grider_schupbach_palmour_2015, title={Static and dynamic performance characterization and comparison of 15 kV SiC MOSFET and 15 kV SiC n-IGBTs}, DOI={10.1109/ispsd.2015.7123431}, abstractNote={This paper presents the static and dynamic performance of 15 kV SiC IGBTs with 2 um and 5 um field-stop buffer layer thicknesses respectively and compares them with 15 kV SiC MOSFET in term of loss and switching capability. Their switching energy for different gate resistors and temperature have been reported and compared. A 5 kHz 10.5 kW 8 kV boost converter has been built and tested using these three devices respectively. The MOSFET based boost converter has the highest efficiency 99.39% which is the highest reported efficiency for a high voltage SiC device based converter. PLECS loss models can be developed for these devices based on the characterization data to simplify the simulation of a variety circuits or applications which potentially utilize these devices.}, booktitle={Proceedings of the international symposium on power semiconductor}, author={Wang, G. Y. and Huang, A. Q. and Wang, F. and Song, X. Q. and Ni, X. J. and Ryu, S. H. and Grider, D. and Schupbach, M. and Palmour, J.}, year={2015}, pages={229–232} }
 @inproceedings{wang_wang_huang_yu_ni_2014, title={A 3.6kV high performance solid state transformer based on 13kV SiC MOSFET}, DOI={10.1109/pedg.2014.6878693}, abstractNote={This paper presents the development of a distribution network solid state transformer (SST) based on high voltage (13kV) SiC MOSFET and JBS diode. This distribution SST is composed with a medium voltage ac/dc rectifier, medium voltage medium frequency dc/dc converter and a low voltage inverter. It's able to be interfaced to 3.6kV distribution grid and output both a 400V dc and 240/120V ac. This paper presents the characterization of the high voltage SiC MOSFET devices, and the design of rectifier and dc/dc converter. The test results of its grid-connected operation including pre-charge, start up, regeneration, etc. are included to show the functionalities of the designed SST prototype.}, booktitle={Ieee international symposium on power electronics for distributed}, author={Wang, F. and Wang, G. Y. and Huang, A. and Yu, Wensong and Ni, X. J.}, year={2014} }
 @article{she_huang_ni_2014, title={Current Sensorless Power Balance Strategy for DC/DC Converters in a Cascaded Multilevel Converter Based Solid State Transformer}, volume={29}, ISSN={["1941-0107"]}, DOI={10.1109/tpel.2013.2256149}, abstractNote={This letter proposes a current sensorless controller for balancing the power in the dc/dc stage of a cascaded multilevel converter based solid state transformer. It is revealed that the equalization of the active power component of duty cycles in the cascaded multilevel rectifier stage can be a good indicator of power balance in the dc/dc stage. Additionally, the power balance of the dc/dc stage can guarantee the voltage balance in the rectifier stage if the differences among the power devices are negligible. Based on this principle, a novel power balance controller without sensing any current in the dc/dc stage is proposed. In the end, experimental results in a seven-level three-stage solid state transformer are provided for verifying the proposed method.}, number={1}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={She, Xu and Huang, Alex Q. and Ni, Xijun}, year={2014}, month={Jan}, pages={17–22} }
 @inproceedings{she_huang_ni_2013, title={A cost effective power sharing strategy for a cascaded multilevel converter based Solid state transformer}, DOI={10.1109/ecce.2013.6646725}, abstractNote={This paper proposes a power sharing strategy for DC/DC stage of a cascaded multilevel converter based solid state transformer. It is revealed that the equalization of the active power component of duty cycles in the cascaded multilevel rectifier stage can be a good indicator of power balance in the DC/DC stage. Additionally, the power balance of the DC/DC stage can guarantee the voltage balance in the rectifier stage if the differences among the power devices are negligible. Based on this principle, a novel power balance controller without sensing any current in the DC/DC stage is proposed. Both simulation and experimental results in a seven-level three-stage solid state transformer are provided for verifying the proposed method.}, booktitle={2013 ieee energy conversion congress and exposition (ecce)}, author={She, X. and Huang, A. Q. and Ni, X. J.}, year={2013}, pages={372–379} }
 @inproceedings{yu_she_ni_wang_huang_2013, title={Power management strategy for DC microgrid interfaced to distribution system based on solid state transformer}, DOI={10.1109/ecce.2013.6647394}, abstractNote={A typical DC microgrid, which can be enabled by Solid State Transformer (SST), is investigated in this paper. One unidirectional DC/DC converter for photovoltaic (PV), one bidirectional DC/DC converters for battery, and a SST based on distribution system level, are included in the proposed DC microgrid system. In order to manage the system operation, a distributed power management strategy is proposed. In the proposed control algorithm, not only the DC microgrid system can interface to the distribution system, but each module in the system can be distributed based on its own characteristics. Experimental results verify that the proposed power management strategy can be applied to a DC microgrid stably and achieve good performance.}, booktitle={2013 ieee energy conversion congress and exposition (ecce)}, author={Yu, X. W. and She, X. and Ni, X. J. and Wang, G. Y. and Huang, A.}, year={2013}, pages={5131–5136} }
 @inproceedings{she_huang_ni_burgos_2012, title={AC Circulating Currents Suppression in Modular Multilevel Converter}, DOI={10.1109/iecon.2012.6388809}, abstractNote={Modular multilevel converter is a next generation multilevel converters for medium to high voltage conversion applications, such as medium voltage motor drive and high voltage direct current transmission. One potential issue of this type of converter is the AC circulating current, which increases the current stress and brings additional conduction loss to the system. This paper proposes modified control architecture for modular multilevel converters, aiming at suppressing the AC components in the circulating current. Specifically, a proportional-resonant type minor loop is incorporated to regulate the most AC components of the circulating current to zero in addition to the DC regulation loop. The proposed minor loop can also be applied to single phase MMC, which is not available in previous methods. Simulation results for a three-phase MMC operating as an inverter are provided to demonstrate the feasibility of the proposed method.}, booktitle={38th annual conference on ieee industrial electronics society (iecon 2012)}, author={She, X. and Huang, A. and Ni, X. J. and Burgos, R.}, year={2012}, pages={191–196} }