Optimal Design of the Bearingless Induction Motor for Industrial Applications

This paper presents a framework for the optimal design of the bearingless induction motor intended for industrial compressor applications. A pole-specific rotor winding and a combined stator winding are used to improve the machine performance. An initial design is constructed by following a standard design procedure for AC machines. Design considerations and motor performance evaluation that are unique to the bearingless induction motor are discussed. The 50 kW, 30,000 r/min bearingless induction motor is optimized using multi-objective evolutionary algorithm based on decomposition (MOEA/D). The Pareto front is shown in terms of torque density, efficiency, and ripple performance. Three optimal designs are selected according to different criteria. The improvement margin and tolerance of an optimal design is further investigated through a local sensitivity analysis. Typical optimized designs are found to have an efficiency of around 95.4% using 29-gauge M-19 steel and require less than 1% of the slot space for suspension current to levitate the rotor shaft.