Model Predictive Control With Common-Mode Voltage Injection for Modular Multilevel Converter

Submodule (SM) capacitor voltage ripple is one of the major concerns in modular multilevel converters (MMCs). Capacitor voltage ripple leads to the double-frequency circulating current (CC) in legs, thereby resulting in a cascading effect of increased peak value of the arm current, semiconductor device stress, and power losses in MMCs. In this study, a model predictive control (MPC) with common-mode voltage (CMV) injection is proposed to minimize capacitor voltage ripple and the magnitude of CC. A discrete-time mathematical model of the MMC with CMV is presented to predict the future behavior of the control variables. The injection of CMV guarantees arm voltage balancing without CC control and long-term stability of MMC without large capacitors. The dynamic and steady-state performances of MPC with CMV injection are verified on an MMC with three-level flying capacitor SMs. A performance comparison between the proposed approach and the conventional MPC is also presented. Simulation and experimental studies show that CMV injection significantly reduces the capacitor voltage ripple and the CC in legs. The proposed approach also improves output voltage and current waveform quality.