An Approach to Reduce the Detent Force of Double-Sided Flat Linear PMSMs

The paper deals with an approach to reduce the detent force of double-sided flat linear permanent magnet synchronous machines (PMSMs). The study is initiated by a finite element analysis (FEA)-based investigation of the detent and normal forces of a conventional concept with aligned PM rows mounted on both mover sides. It is found that while it exhibits a quasi-null normal force, the concept is penalized by a huge detent force. An attempt to reduce such a drawback consisting in shifting the PM rows is proposed. Its effectiveness in reducing the detent force is demonstrated by FEA. However, it leads to a remarkable increase of the normal force. In order to minimize this latter, a second design approach consisting in a unilateral extension of both sides of the stator magnetic circuit, is proposed. It is shown that selecting 50% for both PM shift-to-the pole pitch and stator extension length facing the air gap-to-the pole pitch ratios yields acceptable peak-to-peak values of the detent and normal forces. The force production of the resulting machine is then evaluated and compared to the conventional concept one. In spite of the minimization of the force ripple, its mean value is limited to 50%. An approach consisting in a reconfiguration based on the star of slots of the armature in both stator sides, is proposed and assessed by FEA. As a result, an increase of the mean force as well as a reduction of the force ripple are gained.