Design of spoke-type ferrite interior permanent magnet synchronous machines considering the number of rotor poles

Spoke type is one of the most popular rotor configurations in ferrite interior permanent magnet synchronous machines. In such configuration, the focusing factor of permanent magnet flux is of essential importance to achieve high performance. Large number of rotor poles is usually preferred to boost the air-gap flux density from the low-energy ferrite permanent magnets. Besides, multi-layer magnet configuration is commonly employed to increase the rotor saliency in interior permanent magnet synchronous machines. However, such rotor saliency of interior permanent magnet synchronous machine is also heavily influenced by the number of rotor poles. The novel two-layer ferrite magnet spoke-type structure can harness considerable reluctance torque and enhance the torque density. In this paper, the designs of both conventional one-layer and novel two-layer spoke-type ferrite interior permanent magnet synchronous machines are investigated with particular emphasis on the influences of rotor pole numbers. The machine performances are compared in terms of torque capability, electromagnetic losses, and efficiency. Finally, a prototype machine with such novel two-layer ferrite magnet structure is built and tested to validate the advantageous performances.