Small-signal modeling and control for PWM control of switched reluctance motor drives

The switched reluctance motor (SRM) has been traditionally controlled by either open-loop hysteresis or closed-loop pulse-width-modulation (PWM) current controller. The hysteresis controller needs to vary the switching frequency to maintain constant hysteresis current band, resulting unpleasant audible noises. The PWM controller, however, is difficult to design in terms of proper gains and control bandwidth due to the nonlinear nature of the SRM. In this paper, the AC small-signal modeling technique is proposed for linearization of the SRM model such that a conventional PI controller can be designed accordingly for a PWM current controller. With the linearized SRM model, the duty-cycle to output transfer function can be derived, and the controller can be designed with sufficient stability margin. The proposed PWM controller has been simulated to compare the performance against the conventional hysteresis controller based system. It was found that through the frequency spectrum analysis, the noise spectra in audible range disappeared with the fixed switching frequency PWM controller, but were pronounced with the conventional hysteresis current controller. A hardware prototype was then implemented with a digital signal processor control to verify the quiet nature of the PWM controller running at 20 kHz switching.