Optimal Design of 50kW Concentrated Winding Bearingless Motor

Bearingless motor technology offers an integrated and compact alternative to active magnetic bearings for developing contact-free and oil-free industrial compressor systems. These systems require high speed motors designed for significant power levels. This paper considers the optimal design of a 50kW, 30,000 r/min bearingless motor. This design is based around a topology with a fractional slot-concentrated winding and a surface mount permanent magnet motor (the popular 4-pole, 6-slot design), making it a practical and potentially cost-effective design to manufacture. A parallel no voltage combined winding is designed so that the same coils that create torque can also be used to create suspension forces. The rotor magnets are retained via a carbon fiber banding, which is designed within the proposed optimization process. A multi-physics design framework is developed based around the differential evolution algorithm that considers both the electromagnetic design and the structural integrity of the rotor. Design metrics unique to bearingless motors are described and implemented. The final design achieves a maximum efficiency of nearly 96%, a safety factor of approximately 2 in the rotor structural analysis, and is able to support the rotor weight with only 2.5% of the rated armature current.