A comparison of multicarrier PWM strategies for cascaded and neutral point clamped multilevel inverters

Abstract

Analytical solutions of pulse width modulation (PWM) strategies for multilevel neutral point clamped (NPC) and cascaded inverters are presented. These solutions show that the alternative phase opposition disposition (APOD) PWM strategy for NPC inverters produces the same spectral components as the phase shifted carrier PWM (PSCPWM) strategy for cascaded inverters, when the carrier frequencies are adjusted to achieve the same number of total switch transitions for each inverter over one fundamental cycle. From this understanding, a method is proposed to apply the harmonically superior phase disposition (PD) PWM strategy for NPC inverters to cascaded inverters, to achieve improved harmonic performance for the modulation of cascaded inverters. Both theoretical and experimental results confirming this understanding are presented.