Comparison of Various PWM Techniques for DC Link Capacitors Voltage Balancing of a Three-Level NPC VSI

In this paper, different continuous PWM technique (SPWM), discontinuous PWM techniques (DPWM0, DPWM1, DPWM2, and DPWM3) and zero-sequence voltage injection PWM technique (ZSPWM), are implemented for a three-level NPC voltage source inverter (VSI). The three-level VSI has an inherent problem of DC-link voltage balancing. The voltage balancing can be achieved using different PWM techniques. However, at different modulation index values, different PWM techniques result in minimum voltage difference between the DC link capacitors voltage. The capacitors voltage are compared at different modulation index values using different PWM techniques and based on minimum voltage difference, selection of different PWM techniques over the linear modulation range has been proposed. The simulation results are shown to validate the proposal.