Sensorless Rotor Position Analysis using Resonant Method for Switched Reluctance Motor

Discrete position sensors are undesirable in our automotive applications. We are looking for a sensitive,simple, robust and low cost sensing method for the positioning of a rotor in a doubly salient motor. This paper describes an experimental modeling of the stator phase with regards to the frequency and amplitude of a sinusoidal carrier and an original method based on the principle of inductance measurement in the unenergized phase. A series resonant circuit R L(Theta) C is used . L(Theta) is the phase inductance varying with the rotor position. The capacitor value is determined by Lo.C .omega²=1 (Lo is the minimum phase inductance). The resonant circuit is supplied by a high frequency sinusoidal current generator. A synchronous demodulation technique, based on the extraction of the maximal amplitude, gives us a voltage signal. This component is a direct measure of the angle linked to the phase inductance. The advantages of this method are its simplicity, low cost and robustness. But above all it is the fact that it amplifies the phenomenon of inductance variation, thereby enhancing the accuracy in the measurement of the position angles.