An Inquiry into the Winding Phase-Shifting Technique on the Electromagnetic Performance of Wound-Field Flux Modulation Machines

In this paper, the application of a winding phase-shifting technique to two flux-modulation machines – the wound-field flux switching machine (WFFSM) and the DC-excited Vernier reluctance machine (DCVRM) is investigated. Finite element analysis (FEA) is used to compare the electromagnetic performance between conventional and 30-degree phase-shifted windings. The phase-shifted windings result in reduced average torque for both machines (32.3 Nm and 28.7 Nm decreases for the WFFSM and DCVRM, respectively). The WFFSM shows a minor 4.6% torque ripple reduction with phase-shifting while the DCVRM has a 13% increase. Optimization using genetic algorithms and skewing is more effective, reducing torque ripple by 57-72%. The phase-shifted windings introduce low-order harmonics likely due to the concentrated windings and modulated reluctance torque production. The results indicate the winding phase-shifting technique is incompatible with the modulated reluctance and internal harmonic fields of flux-modulation machines. More research is needed to understand these differences compared to wound-rotor synchronous machines where phase-shifting is effective.