On-Load Voltage Distortion in Fractional-Slot Interior Permanent Magnet Machines.

The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $\beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]