A novel start-up scheme for modular multilevel converter

This paper presents a novel start-up scheme for the modular multilevel converter. Firstly a charging process model is introduced and the process of the proposed start-up scheme is presented. Then the maximum current and current-time formula during the charging process is derived. The mathematical solution of the formulas is used to compare with the results from a three-phase simulation using Matlab/Simulink. By using this method, no auxiliary dc source or extra dc breaker is needed. Finally the proposed start-up scheme is verified on a single phase downscaled MMC prototype. The experiment shows that the proposed method can charge the voltage of each module capacitor to the rated value with smaller surge current.