Variable-flux outer-rotor permanent magnet synchronous motor for in-wheel direct-drive applications

In-wheel direct-drive is the most efficient driving mode for electric vehicles, and it is the trend for applications in the future. In this paper, a novel variable-flux outer-rotor permanent magnet synchronous motor with a hybrid magnetic structure design is developed. Due to the hybrid magnetic pole with Nd-Fe-B and Al-Ni-Co permanent magnet(PM), the air-gap flux can be adjusted by changing the magnetization states of Al-Ni-Co PM, which is beneficial to realize a wide range of speeds and loads from the electromagnetic structure design. Firstly, basic structure features of the motor and the flux-adjusting principle are introduced. The design and calculation method of the PM dimensions is derived based on magnetic circuit analysis. Then the Preisach hysteresis model of Al-Ni-Co PM is described and is adopted to analyze the motor performance with the coupling of the time step finite element method(FEM), and the magnetization are investigated. Finally, the operational performance of the proposed motor is obtained by simulation, which verifies the design.