Analysis of multiphase space vector pulse-width modulation based on multiple d-q spaces concept

Multiphase motors are usually designed to have the concentrated winding and nonsinusoidal airgap flux density distribution in order to maximize the torque per ampere. This means that the phase voltage of a multiphase motor has the nonsinusoidal waveform. Accordingly, the conventional analysis on a multiphase space vector pulse-width modulation (SVPWM), which is confined to a sinusoidal phase voltage, should be extended to a nonsinusoidal phase voltage. In this paper, based on a multiple d-q spaces concept a novel analysis on a multiphase SVPWM to synthesize an arbitrary nonsinusoidal phase voltage is proposed. Throughout this paper, a five-phase inverter is used as a practical example. The basic concepts can be easily extended to an n-phase inverter.

I. Introduction

Kelly et al. [1] mentioned an -phase unified pulse-width modulation (PWM) scheme by the extension of a three-phase unified PWM. In an -phase system, the th harmonic voltage offset can be calculated by averaging between the maximum and minimum reference phase voltages. This voltage offset equally divides the applying times of two zero switching vectors within the sampling interval so that the dc-link voltage utilization can be increased compared to a sine-triangle PWM. In [1], Kelly et al. also verified that an -phase space vector PWM (SVPWM) scheme can be described in terms of the applying times of available switching vectors on the basis of the space vector concept. However, the paper only focuses on how to realize a sinusoidal phase voltage.