Optimization of ring magnet geometry for field harmonic control in electric motors

An optimization algorithm for shaping a multipole, continuous magnet for elimination of one or more harmonics is presented. The magnet is modeled as a continuous ring portion and an optimized section, modeled as a series of thin layers, at each pole. The analytical model investigated consisted of a radially magnetized four-pole motor with a solid ring stator. The algorithm successfully shaped the poles to eliminate selectively the 8th, the 12th, or the 16th harmonic, at the expense of increasing the amplitudes of the other harmonics. The solutions were not unique. A tradeoff in effectiveness existed between the minimum thickness of the continuous ring and the minimum sector angle of the outer pole layer. For thin rings and small outer layer sector angles, an optimum pole shape was readily found. However, if one parameter was too large, then the other had to be decreased for an effective solution to exist