Capacitor voltage balancing algorithm for modular multilevel converters based on voltage fluctuation
DOI：10.7667/PSPC171777
Key Words:modular multilevel converters  voltage fluctuation suppression  capacitor voltage balancing  switching frequency  loss calculation
Author NameAffiliation
LU Yi State Grid Zhejiang Electric Power Co., LTD, Hangzhou 310027, China 
LI Jihong State Grid Zhejiang Electric Power Co., LTD, Hangzhou 310027, China 
QIU Peng State Grid Zhejiang Electric Power Co., LTD, Hangzhou 310027, China 
XU Yuzhe College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China 
XIAO Huangqing College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China 
XU Zheng College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China 
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Abstract:For the capacitor voltage balancing of Modular Multilevel Converters (MMC), in order to suppress the submodule (SM) capacitor voltage fluctuation with lower switching frequency, this paper proposes a mark sorting voltage balancing algorithm. The Mark Sorting Voltage Balancing Algorithm (MSVBA) marks SMs in one arm with two different labels according to the set fluctuation threshold, current state and capacitor voltage of each SM, and then sorts and switches SMs respectively. The fluctuation threshold can be adjusted artificially according to various conditions of the system. Two parameters are proposed to evaluate the performance of capacitor voltage balancing algorithms in this paper, which are the average switching frequency of power devices and the voltage fluctuation rate of arm. A detailed model of 21-level MMC-HVDC test system is built in PSCAD/EMTDC, and the MSVBA is compared with two previous algorithms in the test system. The loss distribution of the MMC under different capacitor voltage balancing algorithms is also calculated. The result proves the validity and the feasibility of the proposed MSVBA. Finally, the performances of the MSVBA with different fluctuation threshold are investigated and some suggestions on parameter selection are given. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 52110417001J).
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