Performance Enhancement in Rewound Industrial Retrofit Solutions for Five- and Six-Phase Permanent Magnet Assisted Synchronous Reluctance Machines

This paper investigates upgrading aging three-phase Permanent Magnet Assisted Synchronous Reluctance Machines (PMaSynRMs) into multiphase configurations—specifically six- and five-phase windings—without modifying the existing stator or rotor laminations. This retrofit supports circular economic principles by extending machine life and reducing material waste and cost. Four configurations are examined: the original three-phase winding, asymmetrical six-phase winding, symmetrical six-phase winding, and five-phase winding. The feasibility of rewinding existing three-phase stators is explored for different slot/pole combinations. Balanced rewound five-phase windings are feasible only when the stator's slot/pole ratio is greater than or equal to 9. Both symmetrical and asymmetrical rewound six-phase windings are possible for all slot/pole combinations, with asymmetrical windings preferred due to their lower MMF harmonics and reduced torque ripple compared to the symmetrical one. Transient simulations in Ansys Maxwell, conducted under healthy and one-phase fault conditions, compare the electromagnetic performance of the four configurations using a 9-slot/pole case study. All variants share identical stator and rotor geometries, ensuring a fair comparison. Although multiphase rewinding incurs a slight cost increase, it results in only a modest 3.8% rise in total drive cost. The five-phase machine offers the highest average torque and efficiency, while the asymmetrical six-phase machine provides the smoothest torque profile and superior fault tolerance. The symmetrical six-phase machine also delivers strong fault performance. In contrast, the original three-phase machine exhibits increased torque ripple and reduced torque output under fault conditions. Experimental results validate the simulation findings.