A Capacitor Voltage Balancing Strategy for a Five Level Hybrid-Clamped Inverter

Five-level hybrid-clamped (5L-HC) inverter is a newly proposed topology which is suitable for high-performance medium-voltage drives. This paper presents a capacitor voltage balancing strategy for a 5L-HC inverter, including the voltage balancing of DC-link capacitors and flying capacitors. Classic phase-shifted PWM is used to control this converter and a mean value model of flying capacitor and neutral point currents is established. The voltages across the central DC-link and flying capacitors are regulated by adjusting the width of four PWM signals, which varies the operation time of redundant switching states in each switching period essentially. The relationship between the neutral-point currents and the output voltage is also studied and the upper and lower DC-link capacitor voltages are balanced by zero-sequence voltage injection. Experimental results are presented to verify the validity of this strategy.