Comparison Between Dual-Permanent-Magnet-Excited Machines With Fewer Stator Poles and Fewer Rotor Poles

The purpose of this paper is to quantitatively compare two types of dual-permanent-magnet-excited (DPME) machines, one is with fewer stator poles and the other is with fewer rotor poles. Four different magnetization patterns of permanent magnets (PMs) are considered. Calculation results obtained using finite-element analysis demonstrate that with exactly the same usage of magnets and copper windings, the DPME machine with fewer rotor poles can offer significantly higher electromagnetic torque than that with fewer stator poles, and the torque ripple of the DPME machine with fewer rotor poles is lower than that with fewer stator poles. Another finding is that DPME machines can offer satisfactorily high-torque capability only when the two sets of PMs are with the same magnetization directions.