Novel Virtual Winding Current Controller for Suppression of Linear Permanent Magnet Machine Electromagnetic Thrust Ripple

Thrust force ripple, including no-load detent force and electromagnetic thrust ripple, worsens the precision of linear permanent magnet machine (LPMM) control system. Asymmetrical current injection algorithm has been proposed for the suppression of electromagnetic thrust ripple, and the key point of the algorithm is positive- and negative-sequence (PNS) current closed-loop control. To achieve better steady-state and dynamic performance, a novel high-bandwidth current controller is proposed in this article. A dual three-phase control system composed of three-phase virtual winding and the three-phase LPMM is introduced. According to the dual three-phase topology, PNS components are decoupled by a novel coordinate transformation, and the proposed controller avoids the use of filters or sophisticated algorithms for extraction of PNS currents. Experimental results based on a linear Vernier permanent magnet machine are presented. It verifies that the asymmetrical current control strategy based on the novel PNS current controller reduces electromagnetic thrust ripple by more than 60% compared with symmetrical three-phase current control.

I. Introduction

Compared with rotating machines used in linear applications, linear machines can reach higher efficiency because of the removal of the transmission mechanism. They are more and more widely applied in industrial and military applications, replacing the ball screw.