Analytical Prediction of the No-Load Operation Features of Tubular-Linear Permanent Magnet Synchronous Machines

This paper is aimed at an analytical approach to predict the no-load operation features of tubular-linear permanent magnet synchronous machines (T-LPMSMs). These are currently considered as viable candidates for wave energy conversion. The developed approach is based on the derivation of the air-gap flux density, considering both the first- and second-type modified Bessel functions of appropriate orders. Following its formulation, the air-gap flux density is applied for the prediction of the no-load operation features, with a focus on the cogging force, the phase flux linkages, and the back electromotive forces. A case study is treated considering three axial arrangements of a T-LPMSM, such as the case of an infinite length machine, the case of a finite length machine, and the case of a finite length machine enabling a quasi-cancellation of the end effect. A comparison between the analytically predicted features and those numerically computed by a 2-D finite-element analysis has led to good agreement.