An approach to reduce the cogging force in tubular linear PM synchronous machines

The paper is aimed at an approach to reduce the cogging force in tubular linear permanent magnet synchronous machines (T-LPMSMs). An analytic prediction of the air gap flux density distribution is developed in a first step, considering the case of slottless machine and the case where the slotting effect is taken into consideration. The established model enables, thanks to a simple formulation, the assessment of the cogging force assuming an “infinite” length machine. Then, the influence of the end effect on the cogging force is investigated in the case of the real machine. The study is extended to a cogging force reduction approach devoted to a quasi-cancellation of the end effect. It consists in a two-step procedure, such that: (i) achieving a 2π/3-shift between the armature winding flux linkages by arranging the ratio of the stator pole pitch to the mover one, and (ii) balancing the amplitudes of these flux linkages by extending the stator magnetic circuit with teeth of appropriate dimensions. The cogging force prediction of the T-LPMSM following the quasi-cancellation of its end effect highlights the effectiveness of the proposed approach.