Selective harmonic elimination strategy for cascaded H-bridge five-level inverter with arbitrary power sharing among the cells

Abstract

Selective harmonic elimination PWM (SHEPWM) is a well-known fundamental frequency switching method for cascaded multilevel inverters. The main goal in the conventional SHEPWM is to eliminate some lower order harmonics of the output voltage while the fundamental component is satisfied. Thus, this method only regards the inverter output voltage quality, which is not sufficient in many applications. Different cells of the cascaded H-bridge multilevel inverter are supplied by isolated dc sources which may have different amounts of power. To deliver maximum power of these sources to a load or network, power should be properly shared among the cells. This study presents a modified SHEPWM method to control quality of the output voltage of the cascaded H-bridge five-level inverter in wide range of the modulation index while desired power sharing among the cells is also considered as the main priority in the whole range of the modulation index. The method forces new constraint in obtaining optimal switching angles and it may require additional switching. To study the problem, a genetic algorithm optimisation program, based on the modified method, is employed for a three-phase five-level inverter. Simulation and experimental results show the effectiveness of the proposed switching method.