Comparative Analysis of Rotor Topologies in Variable Flux Machines with Low Coercivity Magnets

Variable Flux Machines enable flux control of low-coercivity permanent magnets by applying inverter-driven demagnetization and remagnetization current pulses. However, the stator current required for remagnetization directly constrains the converter rating and overall system feasibility. In addition, magnetization state regulation may necessitate torque interruption, which is unacceptable in many practical applications. This paper presents a comparative evaluation of four rotor topologies for VFMs, considering their demagnetization and remagnetization current requirements, torque–speed characteristics at different magnetization states, and capability to remagnetize the PMs under load. The results identify key trade-offs among rotor topologies and provide design-oriented guidelines for selecting an appropriate solution in VFM applications. The analysis reveals that the spoke-type rotor is unsuitable, combining the lowest torque capability with the highest remagnetization current demand. The V-type IPM has the highest torque output, but all considered IPM rotor types cannot be remagnetized without torque interruption, which is the key contribution of the paper. In conclusion, the SPM rotor is identified as the best VFM candidate for future development.