Study on Shaft Voltage in Fractional Slot Permanent Magnet Machine With Different Pole and Slot Number Combinations

A novel shaft voltage, which can also be consider the effect of slot, will be induced by the intrinsic electromagnetic structure in some fractional slot permanent magnet machines (FSPMMs) with certain pole and slot number combinations. By the aid of analytical method and finite-element method (FEM), the relationship of the shaft voltage and pole and slot number combinations is investigated and verified. A qualitative expression of the shaft voltage and the characteristic frequencies of the shaft voltage are predicted by the analytical method. The law of pole and slot number combinations which can yield or avoid the shaft voltage is deduced by the analytical method at the same time. By the FEM, the induced shaft voltages in eight FSPMMs with different slot and pole number combinations are calculated, and the results are well agree with the analytical deductions. As a result, the proposed work provides a theoretical foundation for the novel shaft voltage in FSPMMs and a general method to avoid and reduce the shaft voltage by suitable selection of pole and slot number, which can be a reference for FSPMMs design and fault diagnosis.