Design and Analysis of Fractional Pole-Pair Linear Permanent Magnet Machine

A novel concept of fractional pole-pair linear permanent magnet machine (FP-LPM) has been proposed recently. It is found that using a fractional pole-pair number in linear permanent magnet machine (LPM) could effectively reduce slot cogging force as well as back electromotive force (EMF) unbalance. Thus, thrust ripple is curtailed, which improves its thrust quality and enhances its application potential. However, some issues of FP-LPM still remain unsolved, such as phase split and current phase adjustment, and also, structure optimization is different from the traditional topology due to extra auxiliary tooth. This article contributes to giving a detailed designing methodology, including winding arrangement, regulations of choosing slot/pole combination, and effective end optimization method of FP-LPM. Thus, this article can give helpful guidance in designing FP-LPM to satisfy different application demands. Finally, an 18-slot/29-pole FP-LPM vernier machine (FP-LPMVM) is designed and constructed using the proposed method, and the test results verify the research conclusions.