Analysis and minimization of cogging force in tubular transverse flux linear machines for direct drive applications

This paper presents the analysis and minimization of cogging force in a tubular transverse flux linear machine (TTFLM) with permanent magnet excitation developed for direct drive applications. The influence of leading design parameters on the cogging force is revealed, and verified by 3-dimensional finite element computations. It is shown that for the original design, when considering the tradeoff between force density, cogging force, and mechanical constraints, it is difficult to reduce the cogging force to a pretty low level. In view of this, a novel structure, i.e. the machine with quasi-distributed stator segments, is proposed and investigated to minimize the cogging force. It turns out that the proposed structure is capable of increasing the harmonic number, thus reducing the amplitude of the cogging force effectively.