Torque Improvement and Magnet Reduction of Flux Reversal Permanent Magnet Machines

The configurations of permanent magnet (PM) poles and stator slot numbers in flux reversal PM (FRPM) machines are investigated, with particular reference to their effects on torque and PM usage volume. It is found that the methods of consequent-pole (CP) and halving slot number both help to save the PM usage volume and improve the torque per PM volume. Based on the field modulation analysis, the working harmonics of four FRPM machines with different PM poles and slot numbers are identified. The CP structures exhibit higher armature reaction magneto-motive forces (MMFs) but lower PM MMFs, based on which their torques are advantageous with light loadings. Meanwhile, the effective working harmonics can be enhanced by carefully selecting the slot number, contributing to lower PM usage but higher torque. The finite element analysis is conducted to quantitatively compare the four machines, and validate the theoretical predictions. Finally, three FRPM prototype machines are fabricated and measured for experimental verification.