Spherical harmonic analysis of a novel Halbach array PM spherical motor

A design concept of a Halbach array permanent magnet (PM) spherical motor is proposed in this paper. Based on spherical harmonic functions, the three dimensional (3-D) magnetic fields produced by ball-shaped Halbach array rotor and parallel-magnetization rotor are analyzed. The pole-arc coefficient concept for conventional magnet array spherical motor is developed. The optimum pole-arc coefficient of the conventional parallel PM spherical motor is discussed in order to reduce magnetic flux density waveform distortion and increase magnetic flux density. A comparison is made between the Halbach array PM spherical motor and the conventional parallel magnet array spherical motor in terms of spherical harmonic component and amplitude of air gap flux density, which shows that, compared with the latter, the Halbach motor is more effective in improving air gap field distribution. Magnetization angle and arrangement mode of magnetic poles are studied, which lay a foundation for optimum design of Halbach array PM spherical motor.