Research on High-Voltage Large-Capacity Modular Multilevel Converter (MMC) System

Modular multilevel converter (MMC) is a newly introduced topology of multilevel converter with six arms, each of which is formed by a series connection of several chopper-cells and an inductor. This paper first analyzes the topology and working principle of high-voltage large-capacity MMC. Then, a novel control strategy and its system solution are proposed and explained in details, including staircase modulation and control methods on chopper-cells, and two controls on capacitor voltage, which are average balancing and arm-balancing. Based on PSIM, a system simulation platform of 100-level megawatt MMC with 110KV is established, achieving the co-simulation of its topology and control strategy. The validity of the topology as well as the control strategy proposed in this paper is confirmed by the simulation.