Capacitor Voltage Balancing Scheme for Modular Multilevel Matrix Converter Based on Dynamic Compensation of Active Current Reference

The low frequency alternating current (LFAC) is recognized as a highly prospective solution for offshore wind power application due to the better balance between the energy transmission distance, maintenance costs, reliability and etc. The modular multilevel matrix converter (M3C) is considered as a highly suitable topology for implementing the AC-AC conversion in LFAC transmission system. The collaborative operation of cascading H-bridge submodules realizes the instantaneous energy conversion in M3C, while the capacitor voltage balancing of the submodules is the key concern during the conversion process. In this paper, the decoupled model and equivalent circuit schematic of M3C are established. The capacitor voltage characteristic is analyzed in the time domain, and a capacitor voltage balancing scheme based on dynamic compensation of active current reference is proposed. By independently correcting the active current references in each dq subspace, the deviation of average capacitor voltage can be effectively eliminated. The simulation results are presented to verify the feasibility of proposed schemes.