Reduction of Cross-Coupling for Bearingless Doubly Salient Electromagnetic Motor Using Nonsynchronous Rotating Coordinate Transformation

Abstract

The cross-coupling between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -axis suspension forces caused by the salient pole structure leads to unstable suspension control for bearingless doubly salient electromagnetic (BDSEM) motors. In this paper, the cross-coupling characteristics of the 12/8-pole BDSEM motor are analyzed. The inherent orthogonality of the motor structure, as well as of the biased magnetic field, is illustrated. A new control method based on non-synchronous rotating coordinate transformation is proposed. The suspension force characteristics in the proposed non-synchronous rotating frame both under no-load and load conditions are studied by the mathematical model (MM) and finite element (FE) method. A 12/8-pole BDSEM motor and a suspension force controller are developed. The analytical and experimental results show that the suspension force cross-coupling of the BDSEM motor is reduced significantly.