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

The cross-coupling between the
X
- and
Y
-axis suspension forces caused by the salient pole structure leads to unstable suspension control for bearingless doubly salient electromagnetic (BDSEM) motors. In this article, 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 nonsynchronous rotating coordinate transformation is proposed. The suspension force characteristics in the proposed nonsynchronous rotating frame both under no-load and load conditions are studied by the mathematical model and finite element 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.