Assessment of cogging-force-reduction techniques applied to fractional-slot linear permanent magnet motors equipped with non-overlapping windings

Linear permanent magnet (PM) motors have increasingly been used in high performance applications where high accuracy and fast dynamic response are required. However, the presence of cogging force in linear motors compromises position and speed control accuracy, which can be particularly troublesome at low speeds. This study analyses the cogging force characteristics associated with linear PM motors having either single-layer or double-layer non-overlapping windings. It is shown that the effectiveness of cogging force reduction techniques reported in literature is dependent on winding configurations. Linear PM motors with single-layer windings generally have better potential for cogging force reduction by employing these techniques. In contrast, linear motors with double-layer windings exhibit considerably higher tooth-ripple cogging forces even when fractional-slot per-pole design is adopted. This, in turn, poses more difficulties in reducing their cogging force.