Performance analysis of a mutually coupled linear switched reluctance machine for direct-drive wave energy conversions

The requirements of high efficiency and environment-friendly behavior for wave energy conversions (WECs) have promoted improving investigations of linear electric machines. As an alternative to these existing linear machines, a mutually coupled linear switched reluctance machine (MCLSRM) for direct-drive WECs is proposed in this paper. An extensive comparative study is carried out between the proposed machine and other two comparative machines. By analyzing the operation principles of the three machines, the flux linkage and electromagnetic force formulas are theoretically derived based on equivalent magnetic circuit models, and discussed with the aid of finite-element analysis. Due to high utilization of the electrical and magnetic circuits, it is possible to find an MCLSRM design with comparable force capability to a traditional linear permanent-magnet (LPM) machine with the same electrical loading and the similar overall volume. Furthermore, two prototypes of different machines of the proposed machine and its LPM counterpart are manufactured for experimental validation. From the comparison results, the proposed MCLSRM has a good performance to extract more power from the prime mover above the rated velocity and is highly economic. The LPM counterpart has higher efficiency due to its lower fundamental flux density.