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 LPMVM is proposed, which takes advantage of the magnetic gearing effect. The proposed double-sided 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. The proposed LPMVM with adjusted end-teeth offers a noteworthy potential in terms of high thrust force density, increased power factor, and reduced thrust force ripple, which makes it a suitable candidate for various direct-drive applications. The proposed LPMVM is compared with a conventional surface-mounted LPMVM and a spoke-type LP-MVM without adjusting end-teeth to verify the superiority of the new structure. Also, transient and steady-state thermal analyses of the proposed LPMVM are conducted to confirm its thermal stability. A two-dimensional finite element analysis (2D-FEA) is adopted to prove the outstanding characteristics of the proposed double-sided spoke-type linear vernier structure.