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

To achieve a wider operation speed range and more flexible flux linkage for long-stroke applications, more linear machines (LMs) have been designed as adjustable excitation in recent years, whose air gap flux can be controlled flexibly by altering the excitation of the machine. Moreover, to further reduce the manufacturing cost of the machine, there is a trend to remove the excitations of the machine from the long secondary part. Variable flux reluctance LMs (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 LM, few existing works contribute to a unified working principle and overall comparative analysis. To summarize and compare the performance of different kinds of VF-RLMs, this article provides a comprehensive overview of 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 been presented, as well as the future research interests and challenges of it.