Influence of longitudinal end effects on electromagnetic performance of an permanent magnet slotless linear launcher

Linear motor has the distinctive feature of structurally limited primary and secondary length, which causes longitudinal end effects in actual operation. And this phenomenon will seriously affect the electromagnetic performance of linear motor especially for large volume devices such as electromagnetic launchers. So the purpose of this paper is to study longitudinal end effects in an interior permanent magnet (PM) slotless linear launcher and proposes some measures for improvement. The longitudinal end effects induced by finite PM secondary can give rise to two mechanisms, uneven airgap magnetic field and partial saturation. The splitting edge magnets method is used to improve the uniformity of flux distribution, and it is also beneficial for enhancing thrust. In addition, we focus on unbalanced phase characteristics stemming from finite primary part in slotless motor with distributed windings. The influence of unbalance inductance on thrust and thrust ripple are investigative based on symmetrical component and energy method. The comprehensive analyses are established to aid the initial design and assessment of performance for PM slotless linear launcher.