Influence of inner/outer stator pole ratio and relative position on electromagnetic performance of partitioned stator switched flux permanent magnet machines

Abstract

Based on the 6-pole outer stator (armature winding-stator), the influence of inner (permanent magnet-stator)/outer stator pole ratio n (n=NIS/NOS), stator relative positions and rotor pole number combinations on electromagnetic performance of partitioned stator switched flux permanent magnet (PM) machines (PS-SFPMMs) is investigated in this paper. Since the armature windings and PMs are located in two separated stators and PMs are stationary, PS-SFPMMs have high fault tolerance capabilities. To maximize the torque performance, the PM of inner stator pole should be aligned with outer stator pole when n is odd while the iron rib of inner stator pole should be aligned with outer stator pole when n is even. No matter what n is selected, the rotor pole number NR can be any integers except the phase number and its multiples. The analysis results indicate that the optimal NR is closed to (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IS</sub> +N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OS</sub> )/2 and it is odd when n is odd while it is even when n is even. Meanwhile, symmetrical phase back-EMF waveform will be obtained when the ratio of Min(N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OS</sub> , N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IS</sub> ) to the greatest common divisor of Min(NOS, NIS) and NR is even. Based on the optimal rotor pole numbers for 6-pole outer stator with different n and corresponding optimal relative position together with same rated copper loss, the average torque is improved by 18.4%, 25.1% and 25.7% respectively in PS-SFPMMs with n equal to 2, 3 and 4 when compared with PS-SFPMM with n equal to 1. The analyses are validated by experiment results of the prototype machine.