@article{li_huang_liang_bhattacharya_2012, title={Analysis and Design of Active NPC (ANPC) Inverters for Fault-Tolerant Operation of High-Power Electrical Drives}, volume={27}, ISSN={["1941-0107"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84855387046&partnerID=MN8TOARS}, DOI={10.1109/tpel.2011.2143430}, abstractNote={Compared with neutral-point-clamped (NPC) inverters, active NPC (ANPC) inverters enable a substantially increased output power and an improved performance at zero speed for high-power electrical drives. This paper analyzes the operation of three-level (3L) ANPC inverters under device failure conditions, and proposes the fault-tolerant strategies to enable continuous operating of the inverters and drive systems under single and multiple device open- and short-failure conditions. Therefore, the reliability and robustness of the electrical drives are greatly improved. Moreover, the proposed solution adds no additional components to standard 3L-ANPC inverters; thus, the cost for robust operation of drives is lower. Simulation and experiment results are provided for verification. Furthermore, a comprehensive comparison for the reliability function of 3L-ANPC and 3L-NPC inverters is presented. The results show that 3L-ANPC inverters have higher reliability than 3L-NPC inverters when a derating is allowed for the drive system under fault-tolerant operation. If a derated operation is not allowed, the two inverters have similar reliability for device open failure, while 3L-NPC inverters have higher reliability than 3L-ANPC inverters for device short failure.}, number={2}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Li, Jun and Huang, Alex Q. and Liang, Zhigang and Bhattacharya, Subhashish}, year={2012}, month={Feb} }
 @inproceedings{liang_huang_guo_2012, title={High efficiency switched capacitor buck-boost converter for PV application}, DOI={10.1109/apec.2012.6166090}, abstractNote={A switched capacitor buck-boost DC/DC converter is proposed for the parallel connected distributed photovoltaic (PV) power generation application: an uncontrolled switched capacitor resonant converter is in parallel connection with a buck-boost converter where their outputs are summed to support the load. The switched capacitor converter is operated with a fixed conversion gain whereas the buck-boost converter is controlled to do the MPPT regulation and only a small portion of energy flows through it. In order to obtain ZVS for switched capacitor circuit in the full load range, an auxiliary inductor is added. The converter's performance has been evaluated on a 240W experimental prototype. The test results show that 92.5% efficiency is achieved to generate 200V high output voltage from a 60 cells crystalline PV module with Vmpp=30V.}, booktitle={2012 twenty-seventh annual ieee applied power electronics conference and exposition (apec)}, author={Liang, Z. G. and Huang, A. Q. and Guo, R.}, year={2012}, pages={1951–1958} }
 @article{liang_guo_li_huang_2011, title={A High-Efficiency PV Module-Integrated DC/DC Converter for PV Energy Harvest in FREEDM Systems}, volume={26}, ISSN={["1941-0107"]}, DOI={10.1109/tpel.2011.2107581}, abstractNote={The future renewable electric energy delivery and management (FREEDM) system provides a dc interface for alternative energy sources. As a result, photovoltaic (PV) energy can be easily delivered through a dc/dc converter to the FREEDM system's dc bus. The module-integrated converter (MIC) topology is a good candidate for a PV converter designed to work with the FREEDM system. This paper compares the parallel connected dc MIC structure with its counterpart, the series connected MIC architecture. From the presented analysis, the parallel connected architecture was shown to have more advantages. In this paper, a high-efficiency dual mode resonant converter topology is proposed for parallel connected dc MICs. This new resonant converter topology can change resonant modes adaptively depending on the panel operation conditions. The converter achieves zero-voltage switching for primary-side switches and zero-current switching for secondary-side diodes for both resonant modes. The circulation energy is minimized particularly for 5-50% of the rated power level. Thus, the converter can maintain a high efficiency for a wide input range at different output power levels. This study explains the operation principle of the proposed converter and presents a dc gain analysis based on the fundamental harmonic analysis method. A 240-W prototype with an embedded maximum power point tracking controller was built to evaluate the performance of the proposed converter. The prototype's maximum efficiency reaches 96.5% and an efficiency increase of more than 10% under light load conditions is shown when compared with a conventional LLC resonant converter.}, number={3}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Liang, Zhigang and Guo, Rong and Li, Jun and Huang, Alex Q.}, year={2011}, month={Mar}, pages={897–909} }
 @inproceedings{liang_guo_huang_2011, title={A high efficiency DC MIC for PV energy harvest in FREEDM systems}, DOI={10.1109/apec.2011.5744612}, abstractNote={The future renewable electric energy delivery and management (FREEDM) system provides a DC interface for alternative energy sources. As a result, photovoltaic (PV) energy can be easily delivered through a DC/DC converter to the FREEDM system's DC bus, without the requirement of an additional DC/AC inverter. For this PV converter, the module integrated converter (MIC) is a good candidate. In this paper, two types of DC MIC structures, parallel connected MICs and series connected MICs, have been compared; the parallel connected MICs have been shown to have more advantages. Then a high efficiency dual mode resonant converter topology is proposed for parallel connected DC MICs. The new resonant converter can change resonant modes adaptively depending on the panel voltage and generated power level. The operation principle of the proposed converter is explained and a DC gain analysis is performed based on the fundamental harmonic analysis (FHA) method. For performance evaluation, a 240W prototype has been built. Compared to LLC converter, the light load to medium load efficiency has been improved greatly and the maximum efficiency reaches 96.5% in the experiment.}, booktitle={Annual ieee conference on applied power electronics conference and}, author={Liang, Z. G. and Guo, R. and Huang, A. Q.}, year={2011}, pages={301–308} }
 @inproceedings{guo_liang_huang_2011, title={A high efficiency transformerless step-up DC-DC converter with high voltage gain for LED backlighting applications}, DOI={10.1109/apec.2011.5744767}, abstractNote={Single Boost converter has several limitations in driving a long LED string although it can have perfect current match between each LED. Extreme duty cycle and low efficiency are the two major drawbacks. In this paper, a high efficiency step-up DC-DC converter with high voltage gain for LED backlighting applications is proposed. Without using a transformer, a multi-modes charge-pump is cascaded with a Boost converter to achieve high gain. The charge-pump is unregulated and can switch between 1x, 2x, and 3x mode according to the output requirement. The LED current is regulated by controlling the duty cycle of the Boost converter. The charge pump is located at the low current side therefore can have very high efficiency. The Boost converter is located at the low voltage side and can operate at a relatively low duty cycle, thus the efficiency is improved. The proposed solution can achieve high voltage gain as well as high overall efficiency. The control will also be benefited by the two stage solution. Theoretical efficiency derivations are given in this paper. A prototype is built and the experiment shows a maximum 10.5% efficiency improvement when driving 11 LEDs from 2.7V input voltage.}, booktitle={Annual ieee conference on applied power electronics conference and}, author={Guo, R. and Liang, Z. G. and Huang, A. Q.}, year={2011}, pages={1350–1356} }
 @article{zhou_liang_huang_2010, title={A High-Dynamic Range Current Source Gate Driver for Switching-Loss Reduction of High-Side Switch in Buck Converter}, volume={25}, ISSN={["1941-0107"]}, DOI={10.1109/tpel.2009.2039649}, abstractNote={In this letter, a high-dynamic range current source gate driver (HD-CSD) circuit is proposed to reduce the switching loss of the high-side switch in buck converter with wide variation of the gate resistance. Hard switching loss is the major loss in high-side switch and limits the high switching-frequency application of dc-dc converter. Comparing with conventional voltage source gate driver (VSD) and the reported four switches CSD (4S-CSD), the proposed HD-CSD behaves more like the ideal current source driver which can realize the fast switching of power switches to reduce the switching loss. In addition, with proposed HD-CSD, impact of gate resistance that limits the switching speed of the power switch can be greatly reduced. Experimental results are presented to show the power efficiency improvement of buck converter with HD-CSD high-side driver comparing with VSD and 4S-CSD high-side drivers at switching frequency of 1 MHz.}, number={6}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Zhou, Xin and Liang, Zhigang and Huang, Alex}, year={2010}, month={Jun}, pages={1439–1443} }
 @article{liang_alesi_zhou_huang_2010, title={Digital Controller Development for Grid-Tied Photovoltaic Inverter with Model Based Technique}, ISSN={["1048-2334"]}, DOI={10.1109/apec.2010.5433570}, abstractNote={The main objective for a grid-tied photovoltaic (PV) inverter is to feed the harvested energy from PV panels to the grid with high efficiency and high power quality. A digital controller is the “heart” of the PV system: it calculates the maximum power point (MPP) and regulates the output current to meet the utility inter-connection standards. This paper introduced a new approach “model based design” to develop current controller for PV inverter. This design methodology filled the gap between computer simulation and hardware implementation of the digital controller and made an easy way for the implementation of complex and high level algorithm in a digital signal processor (DSP) [1]. The inverter's small signal model in D-Q rotating frame is derived and a double loop current controller is designed. The performance of the developed controller has been verified by both of the simulation in MATLAB and experimental results from a 2kW single phase PV inverter prototype.}, journal={2010 TWENTY-FIFTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC)}, author={Liang, Zhigang and Alesi, Larry and Zhou, Xiaohu and Huang, Alex Q.}, year={2010}, pages={849–853} }
 @inproceedings{liu_p._g._c._huang_langston_steurer_litzenberger_anderson_adapa_et al._2009, title={Controller hardware-in-the-loop validation for a0 10 MVA ETO-based STATCOM for wind farm application}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72449158355&partnerID=MN8TOARS}, DOI={10.1109/ecce.2009.5316033}, abstractNote={This paper reports experimental validation of a Static Synchronous Compensation (STATCOM) by controller hardware-in-the-loop (CHIL) testing with a real-time digital simulator (RTDS). The controller is designed and developed for a 10 MVA STATCOM for voltage regulation at the PCC of a 50 MW wind farm connected to a 69kV utility grid. Emitter Turn-off (ETO) thyristors are switching devices in the multilevel inverter. The STATCOM controller was developed for a cascade multilevel inverter and has been validated on a laboratory test-bench. The CHIL testing of the controller is done with detailed scaled model of the 50 MW wind farm and 69kV utility system. The experimental results from the RTDS for both steady state and dynamic changes in the STATCOM output validate the STATCOM controller design and performance.}, booktitle={2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009}, author={Liu, Y. and P., Liang Z. and G., Song Z. and C., Bhattacharya W. and Huang, S. and Langston, A. and Steurer, J. and Litzenberger, M. and Anderson, W. and Adapa, L. and et al.}, year={2009}, pages={1398–1403} }
 @inproceedings{song_zhou_liang_bhattacharya_huang_2009, title={Modeling and control design of distributed power flow controller based-on per-phase control}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72449137681&partnerID=MN8TOARS}, DOI={10.1109/ecce.2009.5316307}, abstractNote={The distributed power flow controller (DPFC) based-on Emitter Turn-Off (ETO) light converter is one newly proposed solid state power electronics technology based Flexible AC Transmission System (FACTS) devices which is effective to control the active power flow through the transmission lines. This modular DPFC has low cost, high reliability and makes it possible to have the transformerless connection to the existing power grid. In this paper, the development and analysis of modeling techniques and feedback schemes based on per phase control of DPFC are proposed. The simulation results and experimental results show the consistency of the propose model and the feasibility of the feedback control design for the DPFC per-phase operation.}, booktitle={2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009}, author={Song, W. and Zhou, X. and Liang, Z. and Bhattacharya, Subhashish and Huang, A.Q.}, year={2009}, pages={3262–3267} }