Influence of different magnetization manners on rare earth permanent magnet electrical machines with slot skew

The drive motors of lunar rover should possess high efficiency, small volume, high power density and low torque ripple. The surface-mounted rare earth permanent magnet brushless DC motor with skewed stator slot and inner rotor driven by trapezoidal current is one of the ideal choices. The 3D finite element model was adopted to analyze the electrical machines with slot skew commonly, and the computing process was extremely time-consuming due to the huge calculation a-mount. In order to compare the performance of radial magnetization skewed motor with that of parallel magnetization skewed motor at extreme temperatures of lunar surface, a multi-slice model was adopted and a skewed slot was equivalent to a certain number of straight slot units in series. The equivalent model of skewed motor based on improved 2D finite element method was built and an efficient method of performance computation was proposed. The external control circuit with ideal current source was coupled with the minimum geometry research domain to equalize the winding currents in the same slot of straight slot motor units. The realization of the proposed method was simple and timesaving, and the effectiveness was proven by the prototype test. The research shows that the high harmonics of no-load back-EMF and cogging torques are weakened significantly in virtue of the adoption of slot skew, and the amplitudes of no-load back-EMF and air-gap normal flux of parallel magnetization skewed motor are larger than those of radial magnetization skewed motor.