Analysis and reduction of detent force in permanent magnet linear synchronous motor

The finite element analysis is used to predict detent force due to structure factors in a fractional slot structure permanent magnet linear synchronous motor (PMLSM). To reduce the force ripple, three methods are investigated. They are: (1) adjusting the length of primary core; (2) adopting the fractional slot structure; and (3) adjusting the length of PM. Based on the Fourier analysis of the detent force curve as a function of the motor position, the fundamental harmonic component of magnetic forces arising at both side edges of the primary core can be canceled out by adjusting a mover length, and the detent force is reduced significantly. The detent force component resulting from the slotting of the primary core is reduced effectively by adopting the fractional slot structure. The calculated results show that the detent force of a prototypic PMLSM is successfully reduced by the proposed methods.