The asymmetry of the air-gap magnetic field (AGMF) can raise the unbalanced magnetic force (UMF) of the motor, resulting in motor vibration and noise. This paper proposes a four-module permanent magnet synchronous hub motor (FM-PMSHM) with high fault tolerance and high reliability. The UMF and its influence on FM-PMSHM are analyzed during fault-tolerant operation with the asymmetrical AGMF after removing the faulty module(s) under open-circuit faults. The analytical models of AGMF and UMF of the PMSHM are derived by using the air-gap permeability and magnetomotive force model. Then, the proposed FM-PMSHM and its fault-tolerant operation scheme under open-circuit faults are introduced. After that, the UMF of the motor and its influence on the key performances of the motor， such as the output torque， under fault-tolerant conditions are analyzed according to the theoretical analytical model. The simulation results verify the correctness of the analytical method and analyze the UMF and its effect on the performances of FM-PMSHM.

Four-module permanent magnet synchronous hub motor (FM-PMSHM);Unbalanced magnetic force (UMF);Electromagnetic properties;fiber Bragg grating; distributed temperature monitoring; distribution transformer; finite element simulation; hot spot temperature