@article{kolli_parashar_kokkonda_bhattacharya_veliadis_2024, title={Design of Asynchronous Microgrid Power Conditioning System with Gen-3 10 kV SiC MOSFETs for MV Grid Interconnection}, ISSN={["1048-2334"]}, DOI={10.1109/APEC48139.2024.10509274}, journal={2024 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={2024}, pages={514–521} }
 @article{parashar_kolli_kokkonda_kanale_bhattacharya_baliga_2024, title={Dynamic Voltage Balancing Across Series-Connected 10 kV SiC JBS Diodes in Medium Voltage 3L-NPC Power Converter Having Snubberless Series-Connected 10 kV SiC MOSFETs}, volume={5}, ISSN={["2644-1284"]}, url={https://doi.org/10.1109/OJIES.2024.3450509}, DOI={10.1109/OJIES.2024.3450509}, journal={IEEE OPEN JOURNAL OF THE INDUSTRIAL ELECTRONICS SOCIETY}, author={Parashar, Sanket and Kolli, Nithin and Kokkonda, Raj Kumar and Kanale, Ajit and Bhattacharya, Subhashish and Baliga, Bantval Jayant}, year={2024}, pages={1058–1084} }
 @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{parashar_kolli_kokkonda_kanale_bhattacharya_baliga_2024, title={Mitigating Voltage Imbalance Across Series-Connected 10 kV SiC JBS Diodes in a Medium-Voltage High-Power 3L-NPC Converter}, volume={39}, ISSN={["1941-0107"]}, url={https://doi.org/10.1109/TPEL.2023.3339809}, DOI={10.1109/TPEL.2023.3339809}, abstractNote={This article presents a design methodology for RC snubbers to address dynamic voltage imbalance in series-connected 10 kV SiC junction barrier Schottky (JBS) diodes, utilized in a 3-level (3L) neutral point clamped (NPC) converter. The proposed method considers the effect of bus bar inductance, unequal diode junction capacitance, baseplate capacitance, and common mode (CM) choke tied between the heat sink and midpoint of the dc link capacitor on snubber losses and turn-off voltage mismatch across series-connected diodes. In addition, the effect of hard-switched turn-on across complementary SiC mosfets has been considered on snubber loss and dynamic voltage balancing across SiC JBS diodes. The following steps have been used to simplify the RC snubber design: modeling the switching transition across series-connected 10 kV SiC JBS diodes and 10 kV SiC mosfets on two-level clamped inductive switching test setup, modification of snubber capacitor and switching transition model for 3L-NPC topology, using the experimental data, and modification of snubber resistor using experimental data from 3L-NPC setup with CM choke. Key design parameters obtained from the proposed model have been compared with the experimentally obtained data, which validates the accuracy of the model. Experimental results at the 7 kV dc bus show that the designed RC snubber constrains the turn-off voltage mismatch, snubber loss, and turn-on transition time within the specified limit.}, number={3}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Parashar, Sanket and Kolli, Nithin and Kokkonda, Raj Kumar and Kanale, Ajit and Bhattacharya, Subhashish and Baliga, Jay}, year={2024}, month={Mar}, pages={2896–2911} }
 @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{isik_parashar_bhattacharya_2022, title={Fault-Tolerant Control and Isolation Method for NPC-Based AFEC Using Series-Connected 10kV SiC MOSFETs}, volume={10}, ISSN={["2169-3536"]}, url={https://doi.org/10.1109/ACCESS.2022.3190370}, DOI={10.1109/ACCESS.2022.3190370}, abstractNote={Power Conditioning Systems (PCS) based on three-level converters with series-connected 10kV SiC MOSFETs have gained popularity for medium voltage applications with the increase in distributed energy sources. With the use of Silicon Carbide (SiC), a wide bandgap semiconductor composed of Silicon (Si) and Carbon (C), MOSFET increases in power electronics application due to higher switching frequency operations. A high switching frequency such as 10 kHz or more leads to a reduction in magnetic components’ size and the PCS structure’s size. Therefore, the smaller, modular, and lightweight PCS can be attained for micro-grid integration, EV charging, or high inertia-dominated power grid applications. The three-level NPC (3L-NPC) inverter using series-connected 10kV SiC MOSFET is a suitable topology for coupling the PCS with the medium-voltage utility grid. The converter’s pole sustainability increases with the two series-connected switches, yet the switches are still sensitive and prone to malfunction under various environmental and mechanical causes. Therefore, a meticulous fault isolation and coordination design may be necessary for the front-end converter for possible switch faults in the converter poles. A well-designed fault-tolerant controller may sustain the converter operation under fault conditions while protecting the healthy parts of the converter. Besides, it minimizes the harmful effects of fault on the grid side and increases the system availability. This paper analyzes short and open circuit switch faults that might occur in the PCS. Accordingly, a fault-tolerant method and a fault isolation method are proposed. The proposed methods are verified with Saber™ and the Real-Time Digital Simulator simulation platforms.}, journal={IEEE ACCESS}, author={Isik, Semih and Parashar, Sanket and Bhattacharya, Subhashish}, year={2022}, pages={73893–73906} }
 @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{isik_parashar_bhattacharya_2021, title={Design of a Fault-tolerant Controller for Three-phase Active front End Converter used for Power Conditioning Applications}, ISSN={["1048-2334"]}, DOI={10.1109/APEC42165.2021.9487291}, abstractNote={Recently, an asynchronous micro-grid PCS, enabled by 10kV SiC MOSFETs, has become an exciting research area. The PCS is lightweight and modular technology due to its high switching frequency, 10 kHz or more. Therefore, it can be manufactured and transported at a relatively lower cost. The integration of the PCS to an MV grid, 13.8kV or more, requires an electrical protection scheme to avoid the converter’s fault. Different types of faults might occur in the converter system, such as switch failures or grid side faults. The converter shut-off might lead to power loss to many customers and higher downtime costs for the utilities during a failure. Thus, alternative fault-tolerant techniques are necessary to sustain the converter operation under faulty conditions. This paper investigates short and open circuit switch conditions occurring in 3L-NPC converter topology. Large and small-signal converter models are derived for a given failure. A fault-tolerant controller is designed based on the symmetrical components, and it limits the fault current under the desired limit. A closed-loop simulation of the PCS at 22 kV DC bus and the 10A load current is performed at the RTDS and CHIL setup. Individual switch failures are tested in the RTDS and compared with offline simulation results. The effectiveness of the controller is validated in PLECS.}, journal={2021 THIRTY-SIXTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC 2021)}, author={Isik, Semih and Parashar, Sanket and Bhattacharya, Subhashish}, year={2021}, pages={2804–2811} }
 @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} }
 @article{krishna_kumar_parashar_bhattacharya_2021, title={Performance Evaluation of a Novel High Voltage Monolithically Integrated SiC MOSFET-DIODE for Solar String Inverters}, ISSN={["2150-6078"]}, DOI={10.1109/ECCE-Asia49820.2021.9479330}, abstractNote={There has been an increase in large-scale solar power plants around the world. Most large-scale solar power plants operate at a DC bus voltage of 1000Vor less. It has been shown in current literature that an increase in DC bus voltage enhances the performance of the solar string inverters. The commercially available Si-based string inverters use complex multi-level inverter topologies to reduce the filtering requirements, eliminating the high-frequency operation of SiC MOSFETs. But SiC MOSFETs are associated with reverse recovery losses owed to its body diode. A novel device namely, Integrated MOSFET-DIODE was developed to eliminate this loss, where the reverse conduction is through a SiC diode rather than the MOSFET’s body diode. This paper demonstrates the advantages of a novel Integrated MOSFET-DIODE over Si devices and SiC MOSFETs in applying solar string inverters.}, journal={2021 IEEE 12TH ENERGY CONVERSION CONGRESS AND EXPOSITION - ASIA (ECCE ASIA)}, author={Krishna, Vineeth and Kumar, Ashish and Parashar, Sanket and Bhattacharya, Subhashish}, year={2021}, pages={2345–2351} }
 @inproceedings{kumar_parashar_baliga_bhattacharya_2018, title={Single shot avalanche energy characterization of 10kV, 10A 4H-SiC MOSFETs}, volume={2018-March}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85046957199&partnerID=MN8TOARS}, DOI={10.1109/apec.2018.8341404}, abstractNote={Higher switching frequency capability and lower switching loss associated with 10kV 4H-SiC MOSFETs make them attractive for medium voltage applications, mostly in inductive circuits e.g. solid state transformers, grid connectors and high speed machine drives. Due to exposure to inductive circuits, avalanche ruggedness of these MOSFETs needs to be established to improve their reliability in case of unintended unclamped inductive switching. In this paper, the avalanche ruggedness of 10kV, 10A 4H-SiC MOSFETs is established experimentally using single shot unclamped inductive switching. The minimum and the maximum energy is found out for the MOSFET to remain in avalanche without being failed permanently. The junction temperature at the permanent failure is estimated using semiconductor device physics.}, booktitle={Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC}, author={Kumar, A. and Parashar, S. and Baliga, J. and Bhattacharya, Subhashish}, year={2018}, pages={2737–2742} }