Capacitor voltage balancing of five-level ANPC converter based on zero-sequence voltage injection using PS-PWM

This paper presents a capacitor voltage balancing method for the five-level active neutral-point clamped (5L-ANPC) converter using phase-shifted pulse-width modulation (PS-PWM), including the voltage balancing of DC-link capacitors and flying capacitors. With PS-PWM, the series connected switches are operated at fundamental frequency and the other switches are operated at a constant switching frequency. The relationship between the average neutral-point current and zero-sequence voltage is investigated and an optimum zero-sequence voltage can be calculated to regulate the neutral-point potential. The voltage across the flying capacitor is regulated by adjusting the switching duty cycles of two PWM signals, which varies the operation time of redundant switching states in each switching period. Simulation and experimental results are presented to verify the validity of this method.