Modeling and control of radial force in switched reluctance motor

Unbalanced radial force acting on a rotor shaft is undesirable because it causes motor vibrations. Vet, motor vibrations can be reduced with intentionally produced shaft radial force which cancels the existing unbalanced radial forces due to a non-uniform air gap or external load. Due to its special structure, the shaft radial force and torque of a switched reluctance motor can be separately controlled when all pole currents are controlled independently. However, control of SRM radial force is rarely discussed in existing literature. This paper presents a scheme that produces a controlled radial force for a 12/8 pole SRM. In this scheme, mutual inductances between stator poles are included in the control model. The motor torque is controlled with the conventional method, i.e. all poles in the conduction phase are energized with the same current to produce the desired torque. Two extra poles from the descending-inductance phase are energized to produce the desired radial force. The cross-coupling torque produced by the force producing poles is compensated. The experimental results have verified that when controlled with the proposed scheme, the SRM was able to produce a controlled radial force when at standstill or running, and subjected to a load torque.