An Improved Rotor Resistance Identification Method for Magnetic Field Regulation in Bearingless Induction Motor Drives

Bearingless induction motors have combined characteristics of an induction motor and magnetic bearings. Bearingless induction motors tend to suffer from the influence of rotor resistance variation under field-oriented control because magnetic suspension is sensitive to magnetic field rotational position error. In this paper, a novel rotor resistance identification technique based on variables in the magnetic suspension control loop is proposed. The rotor resistance is identified from suspension force command variations under static force generation by suspending an external shaft weight. Thus, a real-time on-line identification of the rotor resistance variation arising out of loading and temperature changes is possible with the regulation of magnetic field direction.