Performance evaluation of carrier rotation strategy in level‐shifted pulse‐width modulation technique

Abstract

Level-shifted pulse-width modulation (LSPWM) technique for single-star bridge cells (SSBCs)-based modular multilevel cascade inverter (MMCI) produces better harmonic performance than the phase-shifted PWM (PSPWM) technique but its applications are limited because of the unequal device conduction periods, which is undesired in high-power applications. To evenly distribute the switching and conduction losses, the switching patterns should be rotated among the H-bridge cells. This study evaluates two possible carrier rotation techniques, which combines the advantages of uniform power distribution among H-bridge cells and equal device conduction periods from PSPWM technique and improved harmonic performance from LSPWM technique. The effectiveness of the two adopted techniques has been established through simulation and experimental studies. To verify the equality in devices conduction periods, algorithms have been proposed. Further, the behaviours of the DC capacitor voltages of individual H-bridges cells of a five-level SSBC-MMCI-based active power filter have been studied with the adopted carrier rotation techniques.