Unbalanced magnetic force analysis of fractional winding permanent magnet synchronous machines

With the spread of electric machines in the automotive, renewable energy, aviation and space industries, studies in this field have accelerated. Fractional winding permanent magnet synchronous machines are frequently preferred in these areas due to its high torque and power density. However, in permanent magnet electric machines with fractional winding pole-slot combination, magnetic flux lines cannot be distributed symmetrically, and this causes the formation of unbalanced magnetic force (UMF) in the air gap between the stator and rotor. UMF can cause mechanical vibration, acoustic noise on machines and wear of the motor shaft over time. In this study, fractional winding permanent magnet synchronous machine designs with s= 2p±1 with different pole-slot combinations were made, UMF analyzes of these machines were carried out with the finite element method (FEA) and Maxwell Stress Tensor and the results were compared. According to the comparison results, it was observed that the UMF value was lower when the number of poles was one more than the number of slots.