Research on torque ripple under healthy and open-circuit fault-tolerant conditions in a PM multiphase machine

In this paper, research into torque ripple production has been undertaken for both the healthy and open-circuit fault- tolerant conditions of a five-phase permanent magnet (PM) machine by using the instantaneous power (I-Power) approach. When only the fundamental component of the phase currents is applied to the phase windings, it has been shown that the 9th and 11th harmonics of the back-electromotive force (back-EMF) causes torque ripples in a five-phase PM machine and its frequency is ten times the frequency of the fundamental phase currents. When the combined fundamental and third harmonic components of the phase currents are applied to the phase windings, it has been shown that the 7th and 13th harmonic of the back-electromotive force (back-EMF) causes additional torque ripples in a five-phase PM machine .These torque ripples under fault-tolerant conditions have been analyzed analytically, as well. It has been proven that there are interactions between the fundamental component of current and the third harmonic component of the back-EMF and vice versa. These interactions cause torque ripples. A finite element analysis (FEA) model of the five-phase PM machine has been done to validate the analytical results.