Effect of stator winding connection of five-phase induction machines on torque ripples under open line condition

One of the main challenges in designing high-power drive systems is the quality of the developed torque. High-torque-ripple magnitudes result in serious vibration and acoustic noise problems that affect the lifetime of a drive train. Multiphase machines intrinsically offer the torque with higher quality and are also being promoted for their high fault tolerant capability when compared with their three-phase counterparts. During open-phase conditions, the induced nonfundamental sequence current components have a detrimental effect on the machine performance especially under open-loop control. Although optimal current control is usually employed to ensure certain optimization criterion, such as minimizing torque ripples, optimizing flux distribution, or minimizing copper loss, are met, it usually entails a sophisticated current controller. This paper studies the effect of a stator winding connection of a five-phase induction machine on the induced torque ripples. Two possible connections, namely, star and pentagon connections are compared under healthy as well as fault conditions with one-line open. The comparison is conducted using both finite-element simulation and experimental results using a 1.5-Hp five-phase prototype induction machine. The comparison shows that the pentagon connection reduces the machine-induced torque ripples and improves the overall machine performance under fault conditions.