Method for circulating current suppression of UPFC based on MMC
                                    LI Zhen1, LI Bin3, HANG Li jun1, YANG Feng yuan2, QIU Jian1, YANG Guang3
(1.School of Electrical Engineering, Hangzhou Dianzi University, Hangzhou 310018, China;2.School of Electronic, Information and Electrical Engineering, Shanghai University, Shanghai 200240, China;3.State Grid Jiangsu Electric Power Company Nanjing Power Supply Company, Nanjing 210019, China)

Abstract: Aiming at the serious circulant harmonic problem of the Modular Multilevel Converter （MMC） applied in the unified power flow controller（UPFC）, the suppression of the bridge arm circulation was studied, and the control strategy of the capacitor voltage equalization was summarized. After that, a method to restrain the circulation based on twiceline frequency negative sequence rotating coordinate system was designed. Afterwards, the capability of the designed controller on the Matlab/Simulink platform was verified. The results show that the scheme has a significant effect on the harmonic suppression of second order circulating current, meanwhile, the capacitor voltage is balanced.

Key words: unified power flow controller(UPFC); modular multilevel converter(MMC); capacitor voltage balance; circulating current suppression