Contributions of Stator and Rotor PMs in Dual-PM Machines With Different Stator and Rotor Pole Number Combinations

In this article, contributions of stator and rotor PMs in dual-permanent magnet (PM) machines with different stator/rotor pole number combinations are identified and investigated based on a multi-torque component decomposition method. The relationship between additive and cancellation effects of unmodulated rotor PM field component, contributions of stator and rotor PMs, and stator/rotor pole number combinations is revealed by analytical derivation and finite element analysis. It is found that the rotor PMs contribute more in torque production than the stator PMs when the rotor pole number is lower than the stator pole number due to the additive effect of unmodulated rotor PM field component, while the stator PMs contribute more in torque production than the rotor PMs when the stator pole number is lower than the rotor pole number due to the cancellation effect of unmodulated rotor PM field component. The dual-PM machines with fewer rotor pole number than stator pole number exhibit better electromagnetic performance since the torque production capability of PMs is improved by utilizing the additive effect of unmodulated rotor PM field component. A guideline for selecting stator/rotor pole number combinations to improve torque density is provided. Two prototypes are manufactured and tested to validate the conclusions.