Six-phase induction machines have attracted attention due to their high efficiency and enhanced fault tolerance. Compared to conventional three-phase machines, six-phase drives can operate under the open-circuit of one, two, or even three stator phases, while still generating electromagnetic torque and sustaining mechanical load, although torque ripple, harmonic distortion, and some efficiency loss increase. This behaviour is attributed to the interaction between spatial harmonics, which are largely determined by the machine design and winding configuration, and time harmonics, which are related to the supply scheme of the pulse-width modulation inverter.
This article presents a current and torque harmonic analysis of six-phase induction machines with pulse-width modulation inverter supply, based on the interaction of spatial and time harmonics. The study considers both normal operation and fault scenarios, highlighting the effects of harmonic components on torque pulsations, speed fluctuations, and total harmonic distortion.
The interaction of spatial harmonics of the machine’s with time harmonics from the voltage source inverter with pulse-width modulation causes pulsations in the electromagnetic torque. Under normal operation, spatial harmonics dominate the torque and current waveforms. In single-phase open-circuit faults, the second harmonic becomes dominant due to the negative-sequence component of the air-gap magnetic field, while the 6th and 12th torque harmonics are reduced. In three-phase open-circuit faults, the machine operates under reduced load, and the harmonic spectrum shows lower total harmonic distortion compared to normal operation, with spatial harmonics remaining dominant. These findings highlight the importance of harmonic analysis for optimizing control strategies and improving the overall performance and reliability of six-phase drives. The voltage source inverter with pulse-width modulation has negligible influence under these fault conditions, as higher-order harmonics in the current and torque are insignificant.
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