Optimal Design of Tubular Transverse Flux Motors With Low Cogging Forces for Direct Drive Applications

Linear permanent magnet (PM) motors have increasingly been used in high-performance applications where high accuracy and fast dynamic response are required. However, the presence of cogging force in linear motors compromises position and speed control accuracy, which can be particularly troublesome at low speeds. This paper presents analysis and minimization of cogging force associated with a tubular PM motor with transverse flux configuration. An analytical criterion is brought forward, which allows the impact prediction of leading design parameters on the cogging force in an accurate way. And the validity and results are verified by extensive three-dimensional numerical computations and experimental measurements. It is shown that the cogging force increases along with the PM height. And it is highlighted that the cogging force amplitude is a sinusoidal function of the stator segment length, which is quite different from that in conventional PM machines. This work has provided a basis for cogging force reduction, and will aid the design process of the transverse flux motor, especially when targeting high-performance direct drive applications.