Optimal Pulsewidth Modulation of Nine-Switch Inverter

This paper presents the optimal pulsewidth modulation (PWM) schemes suitable for controlling a nine-switch inverter. Modulation wise, references with smallest offsets added are preferred for common frequency in-phase operation because of its lowest influence in harmonic performance. But for the common frequency operation with phase shift needed, traditional zero sequence harmonic offset cannot increase the total maximum modulation depth available in nine-switch inverter. For both common and variable frequency operations, a combined maximum and minimum 120 discontinuous PWM (DPWM) is proposed as the most efficient modulation scheme due to its unique and significant capability in reducing commutation counts among various DPWM schemes. Simulation and experimental results are presented to verify the proposed theories.