Based on curve fitting method to analyze and calculate the equalizing resistance of sub-modules in series of MMC system

Based on the background of VSC-HVDC system, we analyze the sub-module static voltage balancing feature of modular multilevel converter (MMC). Through the analysis of the existing research results, the static voltage balancing of the sub-modules capacitors are related to the parameters of the equalizing resistance. In this paper, a detailed design method of the equalizing resistance is presented. Through studying the main factors which influencing static voltage balance, testing the input voltage and input current data of power supply, and fitting the test data of the power supply of sub-module, we can get the exact curve fitting function, and using it to analyze and calculate the equalizing resistance of sub-modules in series of MMC system. Based on experiments and simulations, the results show that the design method of equalizing resistance can well realize static voltage balancing of sub-modules in series of MMC system.