Influence of Stator Gap on Electromagnetic Performance of 6-Slot/2-Pole Modular High Speed Permanent Magnet Motor With Toroidal Windings

The 6-slot/2-pole (6s/2p) permanent magnet motors with a diametrically magnetized PM rotor are popular for high speed application. Meanwhile, toroidal winding can not only reduce end-winding length but also eliminate unbalanced magnetic force for short axial length motors. Therefore, the electromagnetic performance of a 6s/2p high speed PM (HSPM) motor with toroidal windings is firstly analyzed, including air-gap flux density, flux linkage, back-EMF, cogging torque and electromagnetic torque. Then, considering modular design for auto-manufacturing, the influence of stator gap and misalignment on the electromagnetic performance is investigated. It shows that the stator gap results in unbalanced three phase back-EMFs, not only amplitudes, but also phase angles. The stator gap increases the equivalent air-gap length and PM flux leakage, which leads to lower air-gap flux density, back-EMF, and average torque. Moreover, the stator gap results in asymmetric air-gap length, which results in large cogging torque. Further, it shows that the misalignment of two stator parts mainly affects the uneven equivalent air-gap length and symmetry of winding configuration, which leads to unbalanced three phase back-EMFs, especially phase angles, and self- and mutual-inductances, as well as rotor PM loss. Experimental results of a prototype motor with/without stator gap and/or misalignment are given to validate the finite element predicted analyses.