Investigations into the performance of multilevel PWM methods at low modulation indices

This paper investigates the performance of several multilevel PWM techniques for inverters, which include step modulation technique, selective harmonic elimination PWM (SHEPWM) method, and the presented virtual stage PWM technique. In general, the level number of multilevel PWM techniques decreases in order to reach low modulation indices. However, the number of eliminated harmonics differs from each other. For the same hardware and level number of PWM waveform, the presented virtual stage PWM technique is superior to other techniques for eliminating more low order harmonics and/or having lower total harmonic distortion (THD). Simulation and experimental results are presented confirming the theoretical analysis.