A rotation-based capacitor-voltage-balancing method for modular multilevel converters

Modular multilevel converters (MMC) are widely applied in HVDC projects. To ensure that MMC works properly, sub-module (SM) capacitor voltages must be balanced. This paper proposes a voltage balancing method, which alternates the driving signals on the IGBTs of SMs in fundamental period or carrier period, to balance the capacitor voltages. Under normal operating conditions, this proposed method doesn't need the capacitor voltages of SMs and arm currents information, therefore it effectively decreases the hardware cost and software complexity of MMC system, and also improves the system reliability. The proposed method is validated by constructing a 5-level 1kW single-phase experimental platform in the laboratory. The experimental results demonstrate the feasibility and effectiveness of proposed voltage balancing method.