Decoupled control of thrust and normal force in a double-layer single-sided linear induction motor

In this paper, a modified force decoupling method for improved servo control of a magnetically suspended double-layer single-sided linear induction motor (LIM) is presented. In this study, the primary is magnetically suspended under and moved along the double-layer secondary which consists of an aluminum plate with a back-iron. In order to decoupled the normal and thrust force, analytical expressions for the forces as function of the slip frequency and the primary current are obtained by curve fitting on steady-state FEM results. From these steady-state force models, the required current amplitude and slip frequency are solved for given force setpoints. The setpoints are generated by a position controller which is designed based on a dynamical model of the LIM. The dynamical model is estimated by injecting noise into a transient FE-model and measurements. Transient FEM simulations and measurements show the effectiveness of the proposed controller and decoupling method when they are used to magnetically suspend and position the LIM.