The Method for Reducing Intrinsic Shaft Voltage by Suitable Selection of Pole-Arc Coefficient in Fractional-Slot Permanent-Magnet Synchronous Machines

This paper presents a method to quickly and accurately deduce the optimal pole-arc coefficient for achieving the maximum suppression of intrinsic shaft voltage in fractional-slot permanent-magnet synchronous machines (FSPMSMs). First, with the aid of the analytical method, not only the pole and slot number combinations which can yield the intrinsic shaft voltage in FSPMSMs but the analytical expression of the intrinsic shaft voltage are derived. Then, the effect of pole-arc coefficient on the intrinsic shaft voltage is investigated, and an optimal pole-arc coefficient which can minimize the intrinsic shaft voltage is calculated. Furthermore, the analytical results are validated by finite element method (FEM) well in 6-pole/9-slot, 8-pole/9-slot, and 8-pole/12-slot FSPMSMs, which indicates that the differences obtained between the optimal pole-arc coefficients by two methods are all less than 10%. In conclusion, considering the rapidity of the analytical method and the precision of the FEM, the analytical method should be used first to deduce an initial value to compress the interval of optimization, then run the calculation iteratively by the FEM to get the exact optimal pole-arc coefficient.