A New Control Strategy for Capacitor Voltage Balance of Hybrid Modular Multilevel Converter

Hybrid Modular Multilevel Converter (MMC) has become the most promising topology in flexible direct current transmission. However, the voltage ripple occurs to the submodule capacitor voltage in normal operation, which makes the loss increasing. To address this issue, this paper analyzes the mechanism of capacitor voltage ripple in a fundamental frequency period from the point of view of energy in detail. In addition, a new control strategy based on arm energy redistribution that can reduce the capacitor voltage ripple is proposed. Simulation results under normal operation based on Simulink/MATLAB prove the feasibility and validity of the proposed control strategy.