Harmonics Analysis and Half-Slot Design of a Bearingless Induction Motor

To reduce the harmonics impact of a bearingless induction motor (BIM), an improved modeling method considering the quadratic terms of the rotor eccentricity and a new stator structure of half-slot are proposed. First, the accurate Maxwell force model consisting of the suspension force and unbalanced magnetic pull is established. The theoretical results are expanded to multipole situations, and the controllable suspension range is discussed. Second, the influence on the Maxwell force amplitude caused by harmonics is analyzed, and the force model is revised and combined with the limit formula solution method for the BIM with concentrated winding. For the BIM with distributed winding, the winding distribution of the rotation system and suspension system are studied, the optimal slot number is found and proved by theoretical derivations, and finally, a novel half-slot structure of the suspension winding is proposed. Theoretical analysis, simulation results, as well as experimental results, all indicate that the proposed method can effectively reduce the influence of the harmonics and further make the Maxwell force and rotor position have lower maximum fluctuation compared with the initial machine.