Composite Sensing Scheme for Permanent Magnet Bearingless Motors Based on Levitating Orthogonal Coordinate System

A proper sensing scheme for the bearingless motor (BM), which is designed for the detection of rotational angle position and translational radial displacements of the rotor, is a vital component from the BM control system point of view. However, adopting independent angle and radial displacement sensing methods make a challenge to the integration of BM system. To further improve integration level of BM, a composite sensing scheme only using four Hall sensors to simultaneously detect the rotational angle position and translational radial displacements of the rotor for BM under levitating orthogonal coordinate system (LOCS) is proposed in this paper, and the proposed composite sensing scheme is easy implementation with digital control by carrying out simple algebraic operation on four Hall signals. Meanwhile, for the problem of eccentricity of the solved levitation center position due to non-ideal factors such as assembly errors, inconsistent device characteristics, etc., a compensation strategy based on the tracking of the minimum levitation current is proposed, and with the target of the minimum anti-eccentric levitation current (AELC), the levitation position of BM is dynamically adjusted in real-time in two dimensions, and the stable levitation at the optimal point (stator geometric center) is finally achieved. Detailed parameter selection principles of the proposed scheme are also given. Simulations and experiments are carried out on a 5000 rpm/150 W BM to verify the effectiveness and superiority of the proposed composite sensing scheme and levitation position eccentricity compensation scheme.