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1. Generalized Architecture of a GaN-Based Modular Multiport Multilevel Flying Capacitor Converter

   https://doi.org/10.1109/TPEL.2023.3269800  

   Tamasas Elrais, Mohamed ; Safayatullah, Md ; Batarseh, Issa ( January 2023 , IEEE Transactions on Power Electronics)

   This paper proposes a generalized Gallium Nitride (GaN) based modular multiport multilevel flying capacitor architecture. In other words, the attractive flying capacitor multilevel (FCML) design and the full-bridge unfolding circuit are employed to develop a multiport multilevel converter architecture that fits various applications. Each module can be designed to contain any combination of AC and DC ports connected through DC-to-DC and DC-to-AC power conversion paths. These conversion paths are FCML topologies that can be designed with any number of levels; the DC-to-AC paths incorporate the full-bridge unfolding circuit. Two example prototypes with open-loop control, three-port and four-port, have verified this generalized architecture. A single module 3 kW three-port four-level prototype with two DC ports and an AC port has achieved a compact size of 11.6 in 3 (4.8 in ×4.3 in × 0.56 in) and a high power density of 258.6 W/in 3 . The three ports are connected through DC-to-AC and DC-to-DC paths that have achieved peak efficiencies of 98.2% and 99.43%, respectively. The total harmonic distortion (THD) of the AC port's voltage and current are 1.26% and 1.23%, respectively. It operates at a high switching frequency of 120 kHz because of the GaN switches and has an actual frequency (inductor's ripple frequency) of 360 kHz thanks to the frequency multiplication effect of the FCML. The four-port prototype contains three DC ports and an AC port and achieved similar high figures of merit. These experimental results of the two prototypes of high efficiency, power density, and compact size are presented in this article and highlight this architecture's promising potential. The choice of the number of modules, ports, and levels depends on the application and its specification; therefore, this proposed generalized structure may serve as a reference design approach for various applications of interest. 

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2. Comparative Analysis of Silicon Carbide and Silicon Switching Devices for Multilevel Cascaded H-Bridge Inverter Application with Battery Energy storage

   https://doi.org/10.1109/PEDG.2018.8447775  

   Mordi, Kenneth ; Mhiesan, Haider ; Umuhoza, Janviere ; Hossain, Md Maksudul ; Farnell, Chris ; Mantooth, H. Alan ( June 2018 , 2018 9th IEEE International Symposium on Power Electronics for Distributed Generation Systems (PEDG))

   This paper investigates the use of power semiconductor devices in a nine - level cascaded H-bridge (CHB) multilevel inverter topology with an integrated battery energy storage system (BESS) for a 13.8kV medium voltage distribution system. In this topology, the bulky conventional step-up 60 Hz transformer is not used. The purpose of this study is to analyze the use of SiC MOSFET and Si IGBT devices in the inverter system to evaluate their respective performances. SiC MOSFET and Si IGBT switching devices are modeled and characterized using Saber® modeling software. The switching losses, thermal performance, and efficiency of the inverter system are investigated, and measurements are obtained from the simulation. Saber® provides a good capability for characterizing semiconductor models in the real world, with great features of computation. A three-phase SiC power MOSFET-based multilevel CHB inverter prototype is presented for experimental verification. In the investigation, better performances of SiC MOSFET devices are recorded. SiC devices demonstrate promising performance at different switching frequency and temperature ranges. 

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3. Development of a 100 kW SiC Switched Tank Converter for Automotive Applications

   Ni, Ze ; Li, Yanchao ; Liu, Chengkun ; Wei, Mengxuan ; Cao, Dong ( September 2019 , 2019 IEEE Energy Conversion Congress and Exposition (ECCE))

   A 300 V to 600 V 100 kW SiC MOSFET based one-cell switched tank converter (STC) is developed as a bidirectional dc-dc power transfer stage between the vehicle battery and the DC-link side of the vehicle dc-ac inverter. A continuous half-load 50 kW and short-period full-load 100 kW operation is targeted. Working principles of the proposed topology are analyzed. Design of the key components such as SiC MOSFET power modules, AC resonant capacitor and inductor is presented. A 100 kW prototype has been assembled and tested. An energy-efficient test platform is designed. The power density of the main power processing part is around 41.7 kW/L. The tested peak and full-load efficiencies are about 98.7% and 97.35%, respectively. The thermal performance has also been evaluated. Both the tested electrical and thermal results are consistent with the theoretical design. 

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4. Evaluation of a Medium-Voltage Grid-Tied Cascaded H-Bridge for Energy Storage Systems Using SiC Switching Devices

   https://doi.org/10.1109/eGRID.2018.8598683  

   Mhiesan, Haider ; Farnell, Chris ; McCann, Roy ; Mantooth, Alan ( November 2018 , Evaluation of a Medium-Voltage Grid-Tied Cascaded H-Bridge for Energy Storage Systems Using SiC Switching Devices)

   This paper presents the study and evaluation of a medium-voltage grid-tied cascaded H-bridge (CHB) three-phase inverter for battery energy storage systems using SiC devices as an enabling technology. The high breakdown voltage capability of SiC devices provide the advantage to significantly minimize the complexity of the CHB multilevel converter, with less power loss compared to when Silicon (Si) devices are used. The topology in this study has been selected based on high voltage SiC devices. In order to reach 13.8 kV, a nine-level CHB is needed when using 6.5 kV SiC MOSFETs. However, if 10 kV SiC MOSFETs are used, only five-levels of the CHB are required. The controls were developed, simulated and verified through an experimental prototype. The results from the scaled-down prototype proved the controls and the verification of the performance of five-level CHB three-phase inverter. For the system reliability, both open-loop and short-circuit faults are analyzed. 

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5. Control Methodologies to Mitigate and Regulate Second-Order Ripples in DC–AC Conversions and Microgrids: A Brief Review

   https://doi.org/10.3390/en16020817  

   Chaturvedi, Shivam ; Wang, Mengqi ; Fan, Yaoyu ; Fulwani, Deepak ; Hollweg, Guilherme Vieira ; Khan, Shahid Aziz ; Su, Wencong ( January 2023 , Energies)

   Second-order ripples occur in the voltage and current during any DC–AC power conversion. These conversions occur in the voltage source inverters (VSIs), current source inverters (CSIs), and various single-stage inverters (SSIs) topologies. The second-order ripples lead to oscillating source node currents and DC bus voltages when there is an interconnection between the AC and DC microgrids or when an AC load is connected to the DC bus of the microgrid. Second-order ripples have various detrimental effects on the sources and the battery storage. In the storage battery, they lead to the depletion of electrodes. They also lead to stress in the converter or inverter components. This may lead to the failure of a component and hence affect the reliability of the system. Furthermore, the second-order ripple currents (SRCs) lead to ripple torque in wind turbines and lead to mechanical stress. SRCs cause a rise in the temperature of photovoltaic panels. An increase in the temperature of PV panels leads to a reduction in the power generated. Furthermore, the second-order voltage and current oscillations lead to a varying maximum power point in PV panels. Hence, the maximum power may not be extracted from it. To mitigate SRCs, oversizing of the components is needed. To improve the lifespan of the sources, storage, and converter components, the SRCs must be mitigated or kept within the desired limits. In the literature, different methodologies have been proposed to mitigate and regulate these second-order ripple components. This manuscript presents a comprehensive review of different effects of second-order ripples on different sources and the methodologies adopted to mitigate the ripples. Different active power decoupling methodologies, virtual impedance-based methodologies, pulse width modulation-based signal injection methodologies, and control methods adopted in distributed power generation methods for DC microgrids have been presented. The application of ripple control methods spans from single converters such as SSIs and VSIs to a network of interconnected converters. Furthermore, different challenges in the field of virtual impedance control and ripple mitigation in distributed power generation environments are discussed. This paper brings a review regarding control methodologies to mitigate and regulate second-order ripples in DC–AC conversions and microgrids. 

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