Development of a Four-Axis Actively Controlled Consequent-Pole-Type Bearingless Motor

In this paper, a design-optimization method for a consequent-pole bearingless motor with a rather large air-gap length is presented. A rotor iron and permanent-magnet structure is proposed which enhances the suspension-force capability during startup. Magnetic saturation in the rotor-iron pole area is solved, and the stator iron is designed so that magnetic saturation is avoided. The design optimization is based on finite-element-method analysis. It is shown that startup is achieved from the touch-down condition in the experiments.