Nonlinear Feedback Control of a Bearingless Brushless DC Motor

Abstract

The demands on bearingless drive configurations concerning performance as well as costs are high. The proposed bearingless brushless DC motor consists of five concentrated coils in a symmetrical arrangement, which generate radial forces and motor torque simultaneously in interaction with a permanent magnet excited disc shaped rotor. Additionally, tilting deflection and the axial position of the rotor are stabilized passively by means of magnetic reluctance forces. Thus, system costs can be reduced significantly compared to a conventional bearingless motor setup, which stabilizes all six degrees of freedom actively. Owing to the nonlinearity of the plant, the use of linear control design methods alone is not suitable for achieving a high operation performance. This paper introduces a new radial position and motor torque control algorithm based on the theory of feedback linearization for a bearingless brushless DC motor. Thereby, the combined model of translatory and rotatory dynamics can be split into independent linear systems by means of a nonlinear change of system coordinates and a static state feedback. Experimental results demonstrate the effectiveness of the proposed approach