Modelling and nonlinear torque control of a switched reluctance machine.

The research of a control to reduce the torque ripple of a Switched Reluctance Machine (SRM) is the main aim of this paper. The SRM is very attractive because of its simple structure. Unfortunately, its polyphase torque is naturally pulsed because of the highly nonlinear electromagnetic characteristics and because the phases have to be successively commutated in order to maintain a continuous rotation. First, the electromagnetic characteristics (torque and flux with regard to the position and the current) have to be very precisely determined. Several experimental methods of characterization are presented. A model based on this experimental electromagnetic characterization is necessary for the synthesis of the control. The models found in the literature, compared with the experimental data, are not adapted to the SRM under study. An original model is then proposed. After defining an appropriate strategy for the phase commutation, the limits of the classical linear control (Proportional Integral controller) are determined. In order to compensate the SRM nonlinearities, a nonlinear torque control has been simulated and tested. Very promising results have been obtained at low and medium speeds.