Phase modulated rotor angle encoder for switched reluctance motor drive

Abstract

Advantages of the switched reluctance motor (SRM) drive makes it an attractive candidate for replacing many adjustable speed ac and dc drives, in both industrial and consumer applications. The switched reluctance drives operate by switching the stator phase currents on and off in synchronism with rotor position. By properly positioning the firing pulses relative to rotor angle, forward, reverse, motoring or generating operations can be obtained. Usually, the desired phase current commutation is achieved by feeding back a rotor position back into a controller from a direct position sensor. However, these shaft position sensors reduce system's reliability and add significantly to the cost of the SRM drives. Various indirect rotor position techniques have appeared in the literature. Some of them, however, are vulnerable to switching noise or are comutationally intensive. In this thesis, a new phase modulation (PM) technique which is robust and not vulnerable to switching noise will be investigated. This method is based on the combination of phase and the amplitude modulation techniques, that are common in communication systems. The instantaneous phase inductance of a non-conducting phase, which has one-to-one relation with rotor position, is extracted in an encoded form using a phase modulator consisting of electronic circuitry. The encoded signal is then decoded to obtain the instantaneous inductance from which the shaft position is determined. An analysis of this technique along with the implementation scheme using a microcontroller is presented in this thesis.