Experimental Voltage Balancing Based Sorting Algorithm for Modular Multilevel Converters

Abstract

Of paramount importance to the proper operation of modular multilevel converter (MMC) is the sub-module (SM) capacitor voltage balancing. Two major approaches proposed to achieve this task are distributed method and centralized method. This paper presents an experimental implementation of the centralized SM capacitor voltage balancing control strategy in MMC based on sorting algorithm. The concept was experimentally demonstrated on a laboratory prototype MMC with four SMs per arm. The results show that the SM capacitor voltages are properly balanced and regulated to their reference values. Furthermore, the resultant output voltage and current waveforms exhibit perfect harmonic performance with fundamental switching frequency; thus confirming the effectiveness of the control method