LAUSR

Thrust force ripple, including no-load detent force and electromagnetic thrust ripple, worsens the precision of the linear permanent magnet machine (LPMM) control system. This article focuses on the elimination of electromagnetic thrust ripple caused by the finite length of the LPMM mover core. On the basis of the asymmetrical current controller for suppression of thrust ripple, the observation of asymmetry plays an important role. The extraction strategy, including the extraction of fundamental frequency current/voltage symmetrical components and an observer for positive- and negative-sequence back electromotive force (EMF), is derived. Compared with off-line data, the proposed control strategy has wider application. Experimental results based on an LVPMM are presented. It verifies that the asymmetrical current control strategy based on the back EMF observer reduces electromagnetic thrust ripple by more than 66%.