Multiple-Degree-of-Freedom Control and Capacitor Voltage Balancing Method of Modular Multilevel Resonant Converter
Sheng Jing1, Chen Cong1, Xiang Xin1, Li Chushan1,2, Li Wuhua1
1. College of Electrical Engineering Zhejiang University Hangzhou 310027 China; 2. Zhejiang University-University of Illinois at Urbana-Champaign Institute Haining 314400 China
Abstract Modular multilevel resonant converters (MMRC) have attracted many studies in the medium voltage area due to the advantages of modular multilevel topology and LLC resonant circuits. However, in the wide input range field, more in-depth research still needs to be conducted on the efficient regulation of this topology. This paper proposed a multi-degree-of-freedom (DOF) voltage regulation control method for a modular multilevel resonant converter. Firstly, the voltage regulation effects and characteristics of switching frequency and modulation index are analyzed. Then, combining both frequency regulation and modulation index control, a wide-range voltage regulation method with multi-degree-of-freedom is proposed, and the hardware parameters and control parameters are designed in detail. Moreover, a supervised capacitor voltage method for ripple suppression is proposed to reveal large capacitor ripple issue under modulation index control. Finally, the effectiveness of the proposed method is verified by a laboratory prototype with a wide input voltage of 8~16kV and an output power of 60kW. The full-load efficiency of the full input voltage range is greater than 96%, and the submodule capacitor voltage ripple is reduced by 60%.
Sheng Jing,Chen Cong,Xiang Xin等. Multiple-Degree-of-Freedom Control and Capacitor Voltage Balancing Method of Modular Multilevel Resonant Converter[J]. Transactions of China Electrotechnical Society, 2022, 37(24): 6216-6229.
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