Analysis of Output Current-Ripple RMS in Multiphase Drives Using Polygon Approach

Multiphase variable-speed drives, supplied from two-level voltage-source inverters (VSIs), are currently considered for a number of industrial applications. Although various multiphase pulsewidth-modulated (PWM) schemes had been recently developed, very little has been reported with regard to the impact of these schemes on harmonic losses (current ripple). This paper presents a general analytical analysis and comparison of harmonic losses of two basic continuous PWM (CPWM) schemes aimed at sinusoidal output-voltage generation. The analysis utilizes the concept of multiple polygon connections, which exist for multiphase systems, and covers all multiphase topologies with an odd phase number and single neutral connection. General harmonic distortion factors (HDFs) of sinusoidal PWM (SPWM) and harmonic injection PWM (HIPWM) are determined and compared for various phase numbers. Theoretical findings are verified by means of simulations and experimentally using a five-phase induction motor drive.