@article{parashar_isik_kolli_kokkonda_bhattacharya_2024, title={Overvoltage Protection of Series-Connected 10kV SiC MOSFETs Following Switch Failures in MV 3L-NPC Converter for Safe Fault Isolation and Shutdown}, volume={12}, ISSN={["2169-3536"]}, url={https://doi.org/10.1109/ACCESS.2024.3351184}, DOI={10.1109/ACCESS.2024.3351184}, abstractNote={This paper presents a design methodology for overvoltage protection across 10kV SiC MOSFETs during turn-off after switch failure in a MV SST Power Conditioning System (PCS) enabled by a cascaded Three-Phase (3P) Three-level (3L) Neutral Point Clamped (NPC) Active Front-End Converter (AFEC) and Dual Active Bridge (DAB) using series-connected 10kV SiC MOSFETs and 10kV SiC JBS diodes. The methodology uses an active voltage clamp at the gate terminal and desat detection technique to identify abrupt open and turn-on switch failures across series-connected 10kV SiC MOSFETs. The analytical model estimates over-current time and turn-off voltage transition by considering bus bar inductance, device base plate capacitance and common mode (CM) choke tied between the heat sink and midpoint of the DC link capacitor. The transition model is used to evaluate the turn-off timing for series-connected MOSFETs, snubber resistors, snubber capacitors, and gate resistors to avoid MOSFET overvoltage during converter shutdown, without affecting the voltage balancing and efficiency during normal operation. The MOSFET turn-off transition during the shutdown has been verified in the Saber RD simulation using the validated Saber RD MAST model of 10kV SiC MOSFETs and 10kV SiC JBS diodes at 13.8kV AC/24kV DC level. The fault isolation and MV SST PCS shutdown have been verified in a real-time environment using HIL setup with Xilinx FPGAs and RTDS, at 13.8kV AC/24kV DC link under PCS operating conditions. The normal operation of 3L-NPC pole hardware with modified snubber resistors, snubber capacitors, and gate resistors is verified by experiments conducted at 7kV DC, 10A load current.}, journal={IEEE ACCESS}, author={Parashar, Sanket and Isik, Semih and Kolli, Nithin and Kokkonda, Raj Kumar and Bhattacharya, Subhashish}, year={2024}, pages={10102–10119} }
 @article{kokkonda_beddingfield_bhattacharya_carsten_varga_2023, title={A Novel Transformer Leakage Energy Recovery Active Clamp Control Technique for High Power AC/DC Flyback Converters}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131320}, abstractNote={A novel twin-pulse active clamp has been proposed for flyback converters that can efficiently recover the transformer leakage energy and route it to the output with reduced clamp current ratings and clamp capacitance compared to existing active clamp methods. This extends the application power range for ac/dc flyback converters by enabling a cost-effective leakage energy recovery method for high-power applications. In the case of a 2.5 kW flyback converter, the proposed clamp offers a potential reduction of the required clamp capacitance by 500x and the clamp current by more than 2x at the expense of a higher peak switch voltage stress when compared to an equivalent conventional active clamp. The operating principle and the design criteria for the proposed clamp method are discussed. Experimental results for a 2.5 kW ac/dc flyback converter prototype with the proposed clamp have been presented, validating the clamp operation. Its performance and efficiency improvement compared to a dissipative clamp with active discharge has also been evaluated over the entire operating region.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Kokkonda, Raj Kumar and Beddingfield, Richard and Bhattacharya, Subhashish and Carsten, Bruce and Varga, Bo}, year={2023}, pages={1238–1245} }
 @article{kokkonda_parashar_bhattacharya_2023, title={Performance Comparison of 10 kV and Series-connected 3.3 kV SiC MOSFETs based VSCs for MV Grid Interfacing Applications}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131385}, abstractNote={The latest HV SiC devices can significantly improve the efficiency and power density of MV grid interfacing converters. A VSC (Voltage Source Converter) with 7.2 kV dc bus can directly interface with a 4160 V grid which can be realized in a 2-level configuration using a 10 kV blocking switch. HV SiC devices such as 6.5 kV and 10 kV SiC MOSFETs are still in their nascency and being used in research applications, whereas 3.3 kV SiC MOSFETs have already been qualified for commercial applications by multiple vendors. In this regard, an equivalent 10 kV switch formed by series connection of three 3.3 kV SiC MOSFETs has been proposed as a potential alternative, and it has been quantitatively compared to a single 10 kV SiC MOSFET. Normalized device parameters have been considered in both cases for a fair comparison. Two types of 10 kV $120\ \mathrm{m}\Omega$ switching cells have been realized through series connected 3.3 kV $40\ \mathrm{m}\Omega$ SiC MOSFETs and parallel connected 10 kV $350\ \mathrm{m}\Omega$ SiC MOSFETs for effective power loss comparison. Experimentally determined device conduction and switching losses have been employed for further efficiency and loss modeling of 3-phase VSCs using both switching cells. The power loss and efficiency trends with load and switching frequency variation have been presented for both cases. The converter power processing capability dependence on the switching frequency has also been compared for both cases.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Kokkonda, Raj Kumar and Parashar, Sanket and Bhattacharya, Subhashish}, year={2023}, pages={995–1002} }
 @article{kolli_parashar_kokkonda_bhattacharya_veliadis_2023, title={Switching Loss Analysis of Three-Phase Three-Level Neutral Point Clamped Converter Pole Enabled by Series-Connected 10 kV SiC MOSFETs}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131392}, abstractNote={The recent advancement in the technology of SiC MOSFETs has spurred interest in designing compact and high switching frequency (10–20 kHz) power converters. However, grid-integration of these power converters at medium voltage (MV) scale would require a conventional transformer. With the development of new high voltage (HV) 10 kV and 15 kV SiC MOSFETs, these converters can directly interface with medium voltage (MV) grids without the need for line-frequency transformers, using simple two-level and three-level topologies. The application of these devices is currently being explored in all MV Applications (8 kV to 30 kV) like Solid State Transformer, MV Drives, Power Conditioning Systems, and MVDC isolators. This paper discusses application of 10 kV SiC MOSFETs and JBS Diodes for enabling Asynchronous Microgrid Power Conditioning System (AMPCS). This medium voltage power converter is enabled by series-connection of devices, in a Three-Level Neutral Point Clamped (3L-NPC) configuration. The voltage balancing of these series-connected devices is achieved by using R C-snubbers. This paper addresses the different conduction modes and switching sequences of a 3L-NPC pole, which is used as building block for the three-phase converter. The switching loss analysis, for various snubber values, is presented for the MOSFETs and the clamping diodes along with experimental results. This research helps in providing an overview of switching losses that are disspated through the device (and heatsink) and through the snubber resistor in a 3L-NPC convertor pole.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Kolli, Nithin and Parashar, Sanket and Kokkonda, Raj Kumar and Bhattacharya, Subhashish and Veliadis, Victor}, year={2023}, pages={2353–2360} }
 @article{kokkonda_bhattacharya_veliadis_panayiotou_2022, title={A SiC based Two-Stage Pulsed Power Converter System for Laser Diode Driving Applications}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE50734.2022.9947820}, abstractNote={This paper discusses the unique driving requirements of a laser diode array and evaluates potential converter configurations to meet those requirements. A two-stage capacitive energy storage based pulsed power converter system consisting of a phase shifted full bridge (PSFB) based capacitor charging power supply (CCPS) and a buck based pulse current source with inductor energy recovery has been adopted. Buck based pulse current source with inductor energy recovery enabled by SiC FETs allows significant reduction in energy loss and required energy storage capacitance when compared to conventionally used linear current regulator. A reconfigured pulse forming circuit has been proposed for the pulse current source which mitigates the effect of the output parasitic inductance on the laser diode without the need for an additional freewheeling diode across the load. A pulsed laser diode driver capable of driving 280 V laser diode arrays at 56 kW peak pulse power has been designed and a full-scale hardware prototype has been built. The complete system has been experimentally validated by generating 50 A current pulses at 250 V output voltage (12.5 kW) which proves the feasibility of the proposed converter configuration for high pulse power laser diode driving applications.}, journal={2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Kokkonda, Raj Kumar and Bhattacharya, Subhashish and Veliadis, Victor and Panayiotou, Chrysanthos}, year={2022} }
 @article{kolli_parashar_kokkonda_anurag_kumar_bhattacharya_veliadis_2021, title={Design Considerations of Three Phase Active Front End Converter for 13.8 kV Asynchronous Microgrid Power Conditioning System enabled by Series Connection of Gen-3 10 kV SiC MOSFETs}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE47101.2021.9594975}, abstractNote={The recent growth in power generation using renewable energy sources has led to extensive research and development of robust and resilient power converters, which can integrate them with the medium voltage (MV) grids (13.8 kV,60Hz). Conventional power converters need a line frequency transformer for their integration to the MV grid, which increases the overall footprint and installation cost of the system. Therefore, a compact and lightweight alternative are required for largescale integration of the renewable energy source to the MV grid. With the advent of high voltage SiC MOSFETs, the operating frequency of grid converter can be increased up to 10-20 kHz, thus significantly reducing the size of filter inductors. The use of these devices in multi-level configurations with series-connected devices facilitates the design of power converters that can interface directly with MV grid, eliminating the need for line frequency transformers. The converter presented in this paper is designed to interface a 13.8 kV three-phase grid to a dc link of 24 kV. A three-level neutral point clamped (3L-NPC) topology enabled by series-connected 10 kV 15 A SiC MOSFETs and 10 kV 15 A SiC JBS diodes is presented. This paper focuses on the advantages, design considerations, and challenges associated with a medium voltage 3L-NPC converter. Experimental results show the successful operation of series-connected 10 kV 15 A SiC MOSFETs and JBS Diodes at medium voltage levels and highlights the series connection that is realized with snubber circuits for voltage balancing.}, journal={2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Kolli, Nithin and Parashar, Sanket and Kokkonda, Raj Kumar and Anurag, Anup and Kumar, Ashish and Bhattacharya, Subhashish and Veliadis, Victor}, year={2021}, pages={1211–1218} }
 @article{kumar_kokkonda_bhattacharya_baliga_veliadis_2021, title={High Voltage Output Characteristics and Short Circuit Robustness of HV SiC MOSFETs}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE47101.2021.9595821}, abstractNote={The short circuit characteristics of the recently developed high voltage (HV) SiC MOSFETs are essential to ensure the proper functioning of the power converters during the short circuit fault conditions. The short circuit failure time can be estimated using the HV output characteristics of the MOSFETs with reasonable assumptions. The HV output characteristics of the 3.3 kV, 6.5 kV, and 10 kV SiC MOSFETs, developed by Wolfspeed, are measured for the first time. The estimated short circuit failure time is 3.5 μs, 7.4 μs and 8.1 μs for the 3.3 kV, 6.5 kV, and 10 kV SiC MOSFETs, respectively at the gate bias of 15 V. The analytical results are closely matching with the experimental short circuit failure results of the 6.5 kV SiC MOSFET. The short circuit robustness of the single 6.5 kV SiC MOSFET is found to be superior to the two series-connected 3.3 kV SiC MOSFETs.}, journal={2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Kumar, Ashish and Kokkonda, Raj Kumar and Bhattacharya, Subhashish and Baliga, Jayant and Veliadis, Victor}, year={2021}, pages={5277–5282} }
 @article{kokkonda_kumar_anurag_kolli_parashar_bhattacharya_2021, title={Medium Voltage Shore-to-Ship Connection System Enabled by Series Connected 3.3 kV SiC MOSFETs}, ISSN={["1048-2334"]}, DOI={10.1109/APEC42165.2021.9487119}, abstractNote={Increasing concern about the environmental impact of ships has made Shore-to-Ship (STS) power an attractive solution for ship owners and port authorities worldwide in reducing emissions at ports. Existing shore-to-ship solutions for 0.1 MVA to 5 MVA applications employ silicon (Si) IGBT based static frequency converters. Recent developments in high voltage silicon carbide (SiC) devices have facilitated improvement in efficiency and power density of medium voltage (MV) converters in various applications. This paper proposes an MV STS system enabled by series connection of three 3.3 kV SiC MOSFETs, which shows the potential for improved power density and efficiency compared to existing Si IGBT based solutions. A 100 kVA 3-phase two-level voltage source converter (VSC) with series connected 3.3 kV SiC MOSFETs is designed and demonstrated. Experimental results for the series connected 3.3kV SiC MOSFET based converter is shown at 6 kV dc link voltage to validate the design and operation of such a system. Successful demonstration of a MV converter system enabled by series connection of high voltage SiC MOSFETs can open up opportunities to replace conventional Si IGBT based converters with SiC MOSFET based converters in applications interfacing with medium voltage grid.}, journal={2021 THIRTY-SIXTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2021)}, author={Kokkonda, Raj Kumar and Kumar, Ashish and Anurag, Anup and Kolli, Nithin and Parashar, Sanket and Bhattacharya, Subhashish}, year={2021}, pages={1380–1387} }