Reluctance Force Magnetic Suspension Characteristics and Control for Cylindrical Rotor Bearingless Motors

In this paper, the modeling and control of reluctance-force-based magnetic suspension in cylindrical rotor, ring-shape air gap, bearingless motors are presented. The full suspension system dynamics, including both the destabilizing force due to the motor field and the active magnetic suspension control forces, are modeled, and a transfer function of the bearingless motor suspension plant is derived. It is shown that the suspension system dynamics in a bearingless motor depend on the motor winding current amplitude. This requires the magnetic suspension controllers to address the changing system dynamics and to stabilize the suspension under different driving conditions. A controller design with its gains changing with the motor winding current amplitude is proposed. The derived model and the proposed controller design are verified by experiments with a hybrid hysteresis-induction type bearingless motor. The derived mathematical model provides an effective basis for loop-shaping control design for the reluctance force-based magnetic suspension systems in bearingless motors. The proposed controller design can stabilize the rotor’s suspension under varying excitation conditions.