Analysis of amplitude modulation methods for sensorless SRM drives

In this paper, the performance of two different sensorless control methods for switched reluctance motor drives based on amplitude modulation techniques are compared. In both the methods, a sinewave diagnostic signal is injected into one of the inactive phases and the rotor position is inferred from the resulting modulated current signal. In the first method, the rotor position sensing is achieved only through hardware means. In the second method, which is introduced in this paper, the diagnostic signal is used to generate an index pulse which occurs every 30° (mech). The rotor position information is obtained at the intermediate positions using the index pulse in conjunction with internal timer available in the microcontroller in order to achieve high resolution. In this paper the position error, resolution, speed range and transient stability of the two methods are systematically analyzed using dynamic model of the 100 V, 500 W, 3000 RPM, 6/4 motor and their advantages and disadvantages are presented. Experimental results are presented in order to validate the two sensorless methods. The analysis results presented in this paper will be useful for the practical design of amplitude modulation based sensorless control schemes for SRM drives