@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{soomro_kumar_chachar_isik_alharbi_2023, title={An Enhanced AC Fault Ride through Scheme for Offshore Wind-Based MMC-HVDC System}, volume={15}, ISSN={["2071-1050"]}, DOI={10.3390/su15118922}, abstractNote={This study presents an improved, communication-free Fault Ride-Through (FRT) strategy for type-3 and type-4 wind turbine integrated modular multilevel converter-based high-voltage direct current (MMC-HVDC) systems in offshore wind power plants (OWPPs). The research aims to enhance the reliability and resilience of OWPPs by ensuring their connection with AC grids remains intact during and after faults. Simulation results conducted on a 580 kV, 850 MW MMC-HVDC system using PSCAD/EMTDC software v.4.6.2 demonstrate quick post-fault recovery operation and the ability to effectively manage DC link and capacitor voltages within safe limits. Furthermore, the circulating current (CC) and capacitor voltage ripple (CVR) remain within acceptable limits, ensuring safe and reliable operation. The study’s major conclusion is that the proposed FRT strategy effectively mitigates the adverse effects of short circuit faults, such as a rapid rise in DC-link voltage, on the performance of the MMC-HVDC system. By promptly suppressing DC-link overvoltage, the proposed FRT scheme prevents compromising the safe operation of various power electronics equipment. These findings highlight the significance of FRT capability in OWPPs and emphasize the practical applicability of the proposed strategy in enhancing the reliability of offshore wind power generation.}, number={11}, journal={SUSTAINABILITY}, author={Soomro, Jahangeer Badar and Kumar, Dileep and Chachar, Faheem Akhtar and Isik, Semih and Alharbi, Mohammed}, year={2023}, month={Jun} }
 @article{nath_isik_burugula_bhattacharya_2023, title={Novel Control for Active Power Compensation using DSCC-MMC based ES-STATCOM}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131288}, abstractNote={In recent years, modular multilevel converters (MMC) have gained popularity for high-power applications such as in flexible AC transmission systems (FACTS) and High Voltage DC (HVDC) applications, due to their scalability and modularity along with high efficiency in handling high-power and high voltage needs of the power grid. In the same domain of applications, one such usage of the MMC-based system is the integration of energy storage with static synchronous compensator (STATCOM) technology (known as ES-STATCOM) for providing active power compensation along with reactive power support to the grid. This paper introduces a novel dynamic model-based control approach to the MMC-based ES-STATCOM for the integration of energy sources with the power grid. The design of various controller elements is based on detailed harmonic evaluations for both dynamic and steady-state operation modes. The design of the circulating current control adds second-harmonic computation of the modulation indexes for the suppression of second-harmonic circulating current. This approach further improves the converter's performance by reducing the fluctuation in the capacitor voltages and eventually the losses. Finally, the operating range of the MMC-based ES-STATCOM system is being discussed, which lays down the operating limit for active power compensation with reactive power compensation given the priority. The functionality of the proposed control architecture is validated through a Real-Time Digital Simulator (RTDS) and Virtex 7-based FPGA controller in a Controller Hardware-in-Loop (C-HIL) environment.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Nath, Harshit and Isik, Semih and Burugula, Vasishta and Bhattacharya, Subhashish}, year={2023}, pages={1102–1108} }
 @article{atif_hassan_shahid_munir_saeed_shahzad_isik_alharbi_2023, title={Simplified Model Predictive Current Control of Four-Level Nested Neutral Point Clamped Converter}, volume={15}, ISSN={["2071-1050"]}, DOI={10.3390/su15020955}, abstractNote={Model predictive control (MPC) is an efficient and growing approach to power converter control. This paper proposes an improved and simplified model predictive current control (MPCC) technique for a four-level nested neutral point clamped (4L-NNPC) converter. Conventional MPCC exhibits better performances as compared to the conventional linear control system such as fast dynamic response, consideration of the system constraints, and nonlinearities. However, the application of the conventional model predictive current control (MPCC) approach on complex systems provokes a significant number of calculations, which is the main hurdle to its practical implementation. To fix this flaw, this paper proposes an effective algorithm to shorten the execution time of the conventional MPCC. In this proposed technique, 216 current predictions of the conventional MPCC are skipped and converted into one required voltage vector (RVV) prediction. With this equivalent reference voltage transformation, the calculation burden of MPCC is significantly reduced, while the output performance is not influenced. The results of the simplified MPCC for the 4L-NNPC converter are analyzed and compared with the conventional MPCC. The computational time is reduced by 19.56% using the simplified MPCC, while keeping an approximately similar error of output currents. The switching frequency and total harmonic distortion (THD) of the proposed method are reduced by 8.16% and 0.07%, respectively, as compared to the conventional technique. These results demonstrate the fact that that the performance of a conventional MPCC is enhanced with the proposed MPCC. The proposed algorithm can be applied to several inverter topologies.}, number={2}, journal={SUSTAINABILITY}, author={Atif, Rao and Hassan, Mannan and Shahid, Muhammad Bilal and Munir, Hafiz Mudassir and Saeed, Mahmoud S. R. and Shahzad, Muhammad and Isik, Semih and Alharbi, Mohammed}, year={2023}, month={Jan} }
 @article{alharbi_isik_alfaris_alkuhayli_bhattacharya_2022, title={A Fault Clearance and Restoration Approach for MMC-Based MTDC Grid}, volume={11}, ISSN={["2079-9292"]}, DOI={10.3390/electronics11142127}, abstractNote={With the growth in continuous energy demand, high-voltage Multi-Terminal DC (MTDC) systems are technically and economically feasible to transmit bulk power and integrate additional energy sources. However, the high vulnerability of the MTDC systems to DC faults, especially pole-to-pole (P2P) faults, is technically challenging. The development of DC fault ride-through techniques such as DC circuit breakers is still challenging due to their high cost and complex operation. This paper presents the DC fault clearance and isolation method for an MMC-based MTDC grid without adopting the high-cost DC circuit breakers. Besides, a restoration sequence is proposed to re-energize the DC grid upon clearing the fault. An MMC-based four-terminal DC grid is implemented in a Control-Hardware-in-Loop (CHIL) environment based on Xilinx Virtex-7 FPGAs and Real-Time Digital Simulator (RTDS). The RTDS results show that the MTDC system satisfactorily rides through DC faults and can safely recover after DC faults.}, number={14}, journal={ELECTRONICS}, author={Alharbi, Mohammed and Isik, Semih and Alfaris, Faris E. and Alkuhayli, Abdulaziz and Bhattacharya, Subhashish}, year={2022}, month={Jul} }
 @article{alharbi_isik_bhattacharya_2022, title={An Equivalent Hybrid Model for a Large-Scale Modular Multilevel Converter and Control Simulations}, volume={10}, ISSN={["2169-3536"]}, url={https://doi.org/10.1109/ACCESS.2022.3176006}, DOI={10.1109/ACCESS.2022.3176006}, abstractNote={Modular multilevel converter (MMC) is adopted mainly for high voltage applications with many power blocks per arm. Before commissioning a large-scale MMC application, it is vital to simulate and study internal and system-level dynamics. However, it is challenging to simulate an MMC with many SMs in EMT simulation tools due to simulation time and computation burden. Therefore, several simplified modeling techniques are proposed to reduce the challenges. Even though the existing models reasonably reduce the computation complexity and simulation time, there are still challenges as the internal dynamics of an MMC cannot be fully captured. On the other hand, the detailed equivalent models capture the internal dynamics, but the simulation complexity and the time increase. Therefore, it is still a need for better, faster, and more accurate simulation models to study the system-level and internal dynamics of an MMC. Therefore, this paper proposes a hybrid simulation model for a large-scale MMC application using a scale-up control structure method. The proposed method is verified in the MATLAB/Simulink simulation tool. Besides, the proposed model is tested and verified at the Real-Time Digital Simulator (RTDS) in a Hardware-in-Loop (HIL) environment.}, journal={IEEE ACCESS}, author={Alharbi, Mohammed and Isik, Semih and Bhattacharya, Subhashish}, year={2022}, pages={53504–53512} }
 @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{isik_burugula_alharbi_azidehak_bhattacharya_2022, title={Implementation of a Modular Distributed Fault-Tolerant Controller for MMC Applications}, volume={15}, ISSN={["1996-1073"]}, DOI={10.3390/en15228427}, abstractNote={Centralized control algorithm limits the hardware flexibility of a modular multilevel converter (MMC). Therefore, distributed control structure has recently started to be seen in the industry application. Even though distributed controller reduces a single point of failure risk compared to the centralized controller, the failure risk of the entire control systems increases due to the number of local controllers. However, the distributed controller can be programmed in such a way as to replace the faulty local controller and sustain the MMC operation. In this paper, the distributed modular fault-tolerant controller is implemented in a laboratory-scale MMC prototype. The controller is built to control four SMs per phase for the proof-of-concept. Therefore, the MMC prototype is also built by two SMs per arm. The controller capability is validated with experimental and the Opal-RT result-time simulator results in a control-hardware-in-loop (CHIL) environment.}, number={22}, journal={ENERGIES}, author={Isik, Semih and Burugula, Vasishta and Alharbi, Mohammed and Azidehak, Ali and Bhattacharya, Subhashish}, year={2022}, month={Nov} }
 @article{alalwani_isik_bhattacharya_2022, title={Inter- area Oscillation Damping Controller for DFIG based Wind Power Plants}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE50734.2022.9947750}, abstractNote={Low-frequency inter-area oscillation is typical for transmission tie-line interconnecting neighboring power systems. Inter-area modes result from generators in one area of the power system oscillating against another group of generators in another area across a weak transmission tie line. Modulating active and reactive power in a wind turbine system equipped with a Doubly Fed Induction Generator (DFIG) may effectively dampen inter-area oscillation. In this paper, modifications of Rotor Side Converter (RSC) control and Grid Side Converter (GSC) control by adding active and reactive Power Oscillation Damping (POD) controllers to improve the dynamic system response are studied. Kundur's well-known two-area system is adopted to demonstrate the impacts of active POD and reactive POD controllers of DFIG on the inter-area oscillation using the PSCAD electromagnetic simulation tool. Besides, system stability is studied based on a frequency sweep using the impedance ratio of the different subsystems inside Kundur's system. The Nyquist Stability Criterion (NSC) is adopted to determine system stability.}, journal={2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Alalwani, Sami and Isik, Semih and Bhattacharya, Subhashish}, year={2022} }
 @article{burugula_isik_bhattacharya_2022, title={Performance Comparison of a Modular Multilevel Converter under Centralized and Decentralized Control Structures}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE50734.2022.9947465}, abstractNote={A Modular Multilevel Converter (MMC) consists of series-connected bi-directional chopper cells with a floating capacitor on each leg. Despite the inherent modularity of the chopper cells, most MMC controllers have been designed based on a Central Controller Unit (CCU) until recently. Using classical linear controllers, the CCU executes the operator-defined setpoints based on measured signals in the outer-level control. Even though a CCU is relatively fast and has fewer communication routes, the CCU retains the scalability and modularity features of an MMC as modification of the controller may be challenging. For this reason, the decentralized control structure has been considered for the recent MMC applications to utilize the scalability and modularity features of an MMC effectively. The decentralized controllers introduce delays, especially for the circulating current, due to the local controllers, so the delays may drastically affect the MMC currents. In this paper, the centralized and the decentralized control structures are implemented and their effects in the arm and the circulating currents are investigated for an MMC operation.}, journal={2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Burugula, Vasishta and Isik, Semih and Bhattacharya, Subhashish}, year={2022} }
 @article{alharbi_isik_alkuhayli_bhattacharya_2022, title={Power Ripple Control Method for Modular Multilevel Converter under Grid Imbalances}, volume={15}, ISSN={["1996-1073"]}, DOI={10.3390/en15103535}, abstractNote={Modular multilevel converters (MMCs) are primarily adopted for high-voltage applications, and are highly desired to be operated even under fault conditions. Researchers focused on improving current controllers to reduce the adverse effects of faults. Vector control in the DQ reference domain is generally adopted to control the MMC applications. Under unstable grid conditions, it is challenging to control double-line frequency oscillations in the DQ reference frame. Therefore, active power fluctuations are observed in the active power due to the uncontrolled AC component’s double line frequency component. This paper proposes removing the active power’s double-line frequency under unbalanced grid conditions during DQ transformation. Feedforward and feedback control methods are proposed to eliminate ripple in active power under fault conditions. An extraction method for AC components is also proposed for the power ripple control to eliminate the phase error occurring with the conventional high-pass filters. The system’s stability with the proposed controller is tested and compared with a traditional MMC controller using the Nyquist stability criterion. A real-time digital simulator (RTDS) and Xilinx Virtex 7-based FPGA were used to verify the proposed control methods under single-line-to-ground (SLG) faults.}, number={10}, journal={ENERGIES}, author={Alharbi, Mohammed and Isik, Semih and Alkuhayli, Abdulaziz and Bhattacharya, Subhashish}, year={2022}, month={May} }
 @article{aljumah_isik_alshammari_bhattacharya_2022, title={SiC-based Isolated Three-port DC-DC Converter Implementation for MV Microgrid Applications}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE50734.2022.9948147}, abstractNote={Integrating microgrids or distributed energy sources into a utility grid requires a meticulous control design. The energy management between the source and the load should be rapidly and carefully controlled. Solid State Transformer (SST) and Power Conditioning System (PCS) are emerging technologies with the development of medium voltage (MV) Silicon Carbide (SiC) power semiconductor devices, which offer high-frequency isolation between MV grids, distributed energy storage, Electric Vehicle (EV) charging, etc. Besides, power flow and power factor can be easily controlled. This paper presents three-port Triple Active Bridge (TAB) applications for micro-grid integration. The system consists of three power conversion stages: AC to DC, DC to DC, and DC to AC. The front-end converters control the DC voltage, and the power flow is dispatched by controlling the TAB. Verification of the system at 24.5 kV DC is tested with the NovaCor, Real-Time Digital Simulator (RTDS).}, journal={2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Aljumah, Osamah and Isik, Semih and Alshammari, Sulaiman and Bhattacharya, Subhashish}, year={2022} }
 @article{alharbi_isik_bhattacharya_2022, title={Submodule Fault-Tolerant Strategy for Modular Multilevel Converter with Scalable Control Structure}, volume={14}, ISSN={["2071-1050"]}, DOI={10.3390/su142416445}, abstractNote={Modular Multilevel Converter (MMC) topology is considered a good candidate for high-voltage applications. One of the reasons is that an MMC can quickly generate a higher voltage with an excellent sine wave with the series connection of many power blocks, called Sub-Modules (SMs). In such applications, the control system of an MMC can be challenging, and the possibility of an SM failure increases. As a result, the reliability and availability of the application reduce over time. To reduce the effects of SM failure, an MMC is usually equipped with Redundant SMs (RSMs). The RSMs are added into MMC arms as regular SMs to increase the application’s reliability and reduce downtime. This paper proposes a unique decentralized SM fault-tolerant control model for RSMs to participate in any SM sets. In an MMC arm, a dedicated controller is assigned to RSMs, while the group of SMs has their local controllers. The controller of the RSMs continually monitors the voltage of all the SM sets in the arm. If there is any failure, the controller of the RSMs activates a requested number of SMs to help local controllers to generate the desired voltage level. The proposed control system significantly reduces local controllers’ computational and communication requirements compared to conventional redundant controllers. The proposed control system is based on a distributed structure, so it does not limit hardware flexibility, such as the scalability and modularity of an MMC system. Besides, the separate controller for the RSMs significantly helps increase the reliability of an MMC application.}, number={24}, journal={SUSTAINABILITY}, author={Alharbi, Mohammed and Isik, Semih and Bhattacharya, Subhashish}, year={2022}, month={Dec} }
 @article{isik_alharbi_bhattacharya_2021, title={An Optimized Circulating Current Control Method Based on PR and PI Controller for MMC Applications}, volume={57}, ISSN={["1939-9367"]}, url={https://doi.org/10.1109/TIA.2021.3092298}, DOI={10.1109/TIA.2021.3092298}, abstractNote={Modular multilevel converter (MMC) is an excellent topology for medium- and high-voltage applications due to its advantages over other multilevel converters. However, the control algorithm design needs meticulous attention as each submodule (SM) capacitor voltage is balanced around their reference. Any voltage inequality between the SM voltage causes the second harmonic-dominated circulating current inside the MMC. The circulating current increases the rms value of the arm currents, component ratings, and the ripple in the capacitor voltages unless it is appropriately controlled. This article proposes an optimized closed-loop circulating current control method based on PR and PI controllers in abc reference frame to prevent high circulating current inside an MMC. The proposed method suppresses the magnitude of circulating current while reducing the ripple in capacitor voltages. The ripple in the dc link voltage is also reduced without any supplementary controller under balanced and unbalanced ac grid conditions. Thus, the proposed circulating current control method reduces the conduction losses and component ratings, while the converter's efficiency and reliability increase. The method's verification is tested on a point-to-point connected MMC-based high voltage direct current system in a real-time simulator with Xilinx FPGA-based MMC emulator and arm controller.}, number={5}, journal={IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Isik, Semih and Alharbi, Mohammed and Bhattacharya, Subhashish}, year={2021}, month={Sep}, pages={5074–5085} }
 @article{isik_alharbi_bhattacharya_2021, title={Comprehensive Analysis of the Control Structures for MMC Applications}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE47101.2021.9595092}, abstractNote={Early MMC applications are controlled with a centralized controller. However, recent MMC controllers are primarily based on a distributed control structure as modularity and scalability features of an MMC can be efficiently utilized with local controllers of the distributed control algorithm. However, the distributed control structure also has a centralized unit for coordinating its local controllers, and the chance of a single point of failure still exists. Therefore, in most recent MMC applications, decentralized control structures are adopted, eliminating the central control unit. Eliminating the central control unit eliminates a single point of failure risk, and the reliability of an MMC theoretically increases. However, this might not always be true for practical MMC applications, as the operation of an MMC relies overall structure of an MMC. Therefore, each arm of an MMC should operate appropriately for the safe and reliable operation of an MMC. This paper evaluates and compares the control structures for MMC applications regarding reliability and area of use.}, journal={2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Isik, Semih and Alharbi, Mohammed and Bhattacharya, Subhashish}, year={2021}, pages={2459–2466} }
 @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{isik_burugula_alharbi_bhattacharya_2021, title={Modular Power Flow Enhancer for Transmission Networks under Unbalanced Power Grid Conditions}, ISSN={["1553-572X"]}, DOI={10.1109/IECON48115.2021.9589894}, abstractNote={The three-phase H-bridge or NPC converters are commonly adopted converter topologies for FACTS devices. Both the converters are classified as multilevel converters capable of producing a three-level AC voltage between the phase and the neutral terminals. Either topology is a good solution in the low voltage environment where it is possible to select a switch capable of blocking the required DC bus voltage. If the converter is designed for a high-voltage application, the design stage of these converters may be challenging due to making composite switches for voltage blocking requirements. Besides, there is a need for a large filter for interfacing these converters with the grid to meet the THD requirements as the operating frequency is the line frequency. Therefore, this paper adopts an MMC as an SSSC to enhance power flow in the transmission network and relieve the transmission line against abnormal situations. Besides, PR-based controllers are presented in αβ0 stationary reference frame to provide reliable operation under unbalanced grid conditions. The effectiveness of the MMC-based SSSC and its controller is modeled in FPGAs and integrated with the RTDS through fiber optic cables.}, journal={IECON 2021 - 47TH ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY}, author={Isik, Semih and Burugula, Vasishta and Alharbi, Mohammed and Bhattacharya, Subhashish}, year={2021} }
 @article{isik_bhattacharya_2021, title={Reliability and Cost Modeling of a Modular Multilevel Converter}, ISSN={["2329-5759"]}, DOI={10.1109/PEDG51384.2021.9494184}, abstractNote={This paper presents an analytical expression to calculate the reliability, cost and loss for Modular Multilevel Converter (MMC) based high voltage applications. A three-terminal DC system is chosen as a case study with different terminal modeling. Terminal 1 is modeled with conventional vector current control and circulating current control. Terminal 2 is modeled with a Fault-Tolerant Controller and dq based circulating current control, and terminal 3 is modeled with a conventional vector current control with no circulating current control. In addition to the control structure, Nearest Level Modulation (NLM) is adopted for each terminal. The MTDC system is investigated based on the total reliability and availability of the terminals. Besides, analytical loss and cost calculations are performed for the three-terminal DC system. Different redundancy techniques for MMC arms are presented, but a 10% active redundancy scheme is adopted in the three-terminal DC system.}, journal={2021 IEEE 12TH INTERNATIONAL SYMPOSIUM ON POWER ELECTRONICS FOR DISTRIBUTED GENERATION SYSTEMS (PEDG)}, author={Isik, Semih and Bhattacharya, Subhashish}, year={2021} }