Comparative assessment of voltage modulation methods for asymmetric six-phase machines

Abstract

A comparative analysis of various techniques for pulse width modulation (PWM) of asymmetrical six-phase permanent magnet synchronous machine (PMSM) is presented in this paper. An asymmetric six-phase PMSM consists of two sets of three-phase winding groups spatially displaced by 30 0 . A current control architecture based on a vector space decomposition (VSD) approach has been utilized for control of PM machine, having individual current controller in each harmonic plane. The output voltage references from current controllers is then used for PWM generation. Various PWM methods from literature, which have been proposed for two-level converter-fed six-phase machines, are then reviewed and most promising 12 and 24 sector SVPWM methods are implemented in the above control architecture. Most common industrial adaptation of six-phase drives consists of two independent three-phase drive units configured to supply two three-phase winding sets. In such situation, it can happen that these drives can have their own independent three-phase modulators synchronized to its own clock. Problems can arise due to independent operation of these two sets of drives while controlling a six-phase machine due to lack of synchronization between these two modulators as well as non-synchronous sampling of machine currents. The main objective of this paper is to compare the performance of above PWM modulators with respect to different situations considering synchronization between reference signals to modulators as well as synchronization between sampling of phase current of two drives.