Analysis of End Effect on Thrust Ripple in Linear Brushless Doubly-Fed Machine

The linear brushless doubly-fed machine (LBDFM) as a novel type of machine has attracted extensive attention in recent years. Due to the complex magnetic fields and end effect, there is rich low-frequency thrust ripple in LBDFM. In order to make the physical process of thrust ripple clear, the end effect on the winding magnetomotive force (MMF) is studied. Firstly, the shifted slot vector affected by the end is obtained. Then, a negative sequence magnetic motive force is analyzed with the certain winding configuration. Finally, the generation of low-frequency thrust ripple is explained. The analysis results are verified by finite element algorithm (FEA) and the proposed method can be applied to most linear machines with short primary.