COMPARISON OF CONTROL STRATEGIES TO MINIMIZE THE TORQUE RIPPLE OF A SWITCHED RELUCTANCE MACHINE
Résumé
ABSTRACT The Switched Reluctance Machine (SRM) presents simple structure with passive rotor without windings nor any magnets. That enables applications in mass production (low production and material costs) or in harsh environments (high temperature...). 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. A torque control associated with an appropriate strategy for the phase commutation is thus sought in order to reduce the torque ripple. Initially, the limits of the classical linear control (Proportional Integral controller) are determined. Then, the performances of the PI controller are improved by means of electromotive forces compensation. Nevertheless, the torque ripple remains significant. In order to compensate for SRM nonlinearities, we propose a nonlinear torque control associated with a suitable commutation strategy. This control has been simulated and experimentally tested. Its performances have been compared with the PI-obtained performances. Very promising results have been obtained at low and medium speeds. However, even with this nonlinear torque control, torque ripple still remains in the presence of voltage saturation. This is precisely why we are presenting herein an original method, which enables compensating for the effects of the feeding-voltage saturation.