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Due to its special structure, the shaft radial force and torque of a switched reluctance motor can be separately controlled when all of the pole currents are independently controlled. In this paper, a control scheme for self-bearing operation of a 12/8 pole SRM drive is proposed. The rotor needs only one bearing for rotation and constraining the axial movement. The other end can move freely in the radial direction but is balanced with the radial force produced by the motor. A model for torque and radial force is derived and used to design the controller. Mutual inductance between the stator poles is included in the analysis to improve the model accuracy. The conduction phase pole currents are energized with phase-shifted sinusoidal currents. Depending on the requested radial force and torque, a descending-inductance phase may also be energized to increase radial force production. The requested force and torque are synthesized from the force and torque produced by these phases. The experimental results demonstrate successful SRM self-bearing operations. The rotor can be effectively balanced to the center of the air gap. The maximum radial position error was about 0.07 mm when the motor was rotating at 1500 r/min under full load torque.
Date of Publication: Nov. 2007