A novel dc voltage charge balance control for cascaded inverters

The authors propose a novel dc voltage charge balance control for cascaded inverters. The proposed controller has two auxiliary control signal features: (1) a balanced discharging of isolated input dc voltages and (2) good flexibility and suitability for the applications when the number of H-bridge inverter modules is changed. When compared with the conventional cascaded inverters, the proposed control can self-adjust to achieve balance charge control without a complex circuit. The system does not require a new design of controller if a new H-bridge inverter module is added to the system for increasing the power capacity, or an H-bridge inverter module is disconnected from the system owing to its failure. The design of the auxiliary control signals is described in detail and implemented in software. Finally, a 7-level cascaded inverter with three dc-ac converter modules was constructed and tested. Analysis, simulations and experimental results are presented to demonstrate the superiority of the proposed system.