Overview on Variable Flux Reluctance Linear Machines for Long- Stroke Applications

To achieve wider operation speed range and more flexible flux linkage for long-stroke applications, more linear machines have been designed as adjustable excitation in recent years, whose air-gap flux can be controlled flexibly by altering excitation of the machine. Moreover, to further reduce the manufacture cost of the machine, there is a trend to remove the excitations of the machine from long secondary part. Variable flux reluctance linear machines (VF-RLMs), which place all of the excitations on the short primary, take merits of low cost, flexible flux and high robustness, and are suitable for many direct-drive linear motion occasions, especially for long stroke applications. However, since VF-RLM is a relatively emerging kind of linear machine, few existing works contributing to unified working principle and overall comparative analysis. To summarize and compare the performance of different kinds of VF-RLMs, this paper provides a comprehensive overview on VF-RLMs including their working principle, machine design and performance evaluations. Meanwhile, a qualitative performance evaluation and comparative study of different kinds of VF-RLM have be presented, as well as the future research interests and challenges of it.