Flux-Oriented Design and Analysis of a Hybrid Rotor Pole Interior Permanent Magnet Motor for In-Wheel Direct Drive

By focusing on the dual requirements of high output torque and wide speed range for the in-wheel motors, a new hybrid rotor pole interior permanent magnet motor is proposed in this paper. Different from the conventional PM in-wheel motors, the rotor poles are recombined by two independent asymmetrical units, the variable flux pole (VFP) unit and non-variable flux pole (NVFP) unit. The VFP unit is capable of realizing the flux regulation whereas the NVFP unit produces the basic effective flux, and thus the high output torque and wide speed range requirements can be satisfied simultaneously. Furthermore, a design principle for maximum flux variation characteristics by slot-pole combination and coil pitch selection is presented. On this basis, for the compound units of such motor, a flux-oriented design method considering multiple operating conditions is proposed, where the speed range and output torque requirements of the motor are decomposed into the independent flux design of the two separated pole units, thus providing a rapid motor design method for in-wheel direct drive applications. In addition, the performances of the proposed motor are evaluated, and a prototype motor is manufactured and tested. The results show good agreement with the analysis and the simulated results.