Cogging force mitigation techniques in a modular linear permanent magnet motor

Modular linear doubly salient permanent magnet motors are well adapted to linear propulsion systems because of their distinct characteristics, such as high efficiency and power density, reduced maintenance and initial cost, low noise and permanent magnet (PM) leakage flux, and fault tolerance capability. However, such motors suffer from high cogging thrust. In this study, various techniques based on previously proposed methods for PM machines are applied on the studied motor and evaluated by using non-linear three-dimensional time-stepping finite element analysis; three novel, optimised techniques are then presented. The techniques presented are based on the minimisation of the variation in air-gap reluctance relative to the displacement. The PM volume and average air-gap length are kept constant in all optimisations. Since the average thrust and thrust ripples under load condition may be affected by cogging reduction techniques, these values are presented for all given techniques. The results show that the proposed techniques not only maintained the average thrust under various loads but also significantly suppressed the thrust ripples for different average thrusts and cogging forces.