Design Modifications for Cogging Force Reduction in Linear Permanent Magnet Machines

The capability of Linear Permanent Magnet (LPM) machines to produce high thrust and power density are being utilized in industrial and defense sectors these days. However, the reluctance variation faced by secondary magnet flux due to primary slotting and end effects produces detent or cogging force, which results in high force ripples, noise and vibrations. This effects the smooth starting and controllability of the machine in accurate positioning applications. This paper proposes some design modifications in the primary slots and slot-openings of LPM machines for detent force minimization. The effect of various design modifications on cogging force, average electromagnetic force and force ripple has been studied using 3-D Finite Element analysis. The analysis results are also compared with that obtained using some existing cogging reduction techniques.