A High Thrust Force Spoke-Type Linear Permanent Magnet Vernier Machine with Reduced Thrust Force Ripple

Abstract

Linear permanent magnet vernier machines (LP-MVMs) have become prevalent in direct-drive applications, such as wave energy harvesting systems and traction applications, owing to their distinctive merit of providing high thrust force at low speeds. In this paper, a novel structure of a double-sided spoke-type linear PM vernier machine is proposed, which takes advantage of the magnetic gearing effect. The proposed doublesided linear machine exploits spoke-type permanent magnets (PMs) and one of the stators is displaced as half of the stator tooth pitch to obtain the flux-focusing effect. The thrust force ripple of the proposed spoke-type LPMVM can be decreased by adjusting the stator end-teeth and mitigating the detrimental impact of the longitudinal effect, leading to a novel structure of LPMVM, which offers high thrust force density, higher power factor, and lower thrust force ripple. The proposed LPMVM with adjusted end-teeth is a suitable candidate for different direct-drive applications. The presented spoke-type linear PM vernier machine is compared with a conventional surface-mounted LPMVM in order to validate the superiority of the new structure. Also, transient and steady-state thermal analyses of the proposed LPMVM are performed to verify the thermal stability of the new machine. A two-dimensional finite element analysis (2D-FEA) is adopted to confirm the outstanding characteristics of the proposed doublesided spoke-type linear vernier structure.