A Dual-Rotor Axial-Flux PM Motor With Equidirectional Toroidal Winding and 3-Slot/4-Pole Unit Block for Torque Density Improvement

In this article, a dual-rotor axial-flux permanent magnetmotor (AFPMM) with equidirectional toroidal winding and 3-slot/4-pole (ETW-3S4P) unit block is proposed to improve the torque density. The advantages of the proposed motor in improving the torque density can be attributed to its high winding factor, low q value of the slot/(pole. phase), and high gear ratio. The motor performance is thoroughly analyzed with reference to the AFPMMs with ETW-3S2P and with conventional concentrated windings and the 3S4P (CW-3S4P). First, the motor structure and the operating mechanism are presented and analyzed. Second, the theoretical analysis is verified by the three-dimensional finite element analysis, and the effect of themagnetic gearing on the torque is also investigated. Then, a detailed performance comparison of AFPMMs with ETW-3S4P, ETW-3S2P, and CW-3S4P, respectively, is carried out. It is shown that the AFPMM with ETW-3S4P has advantages over the other two in terms of torque density, torque quality, flux weakening, and efficiency. Finally, a prototype of the proposed motor is manufactured and tested to validate the correctness of the analyses.