Indirect rotor position detection in a field assisted switched reluctance motor by utilizing aligned resonant frequency

This paper presents a novel method to indirectly detect the rotor position at standstill and also at low speeds in a field assisted switched reluctance motor. In this method, a high frequency sine wave signal is applied to the field assisted winding on the stator and then the phase of induced signals on each phase winding is monitored to detect the rotor position at standstill. The method utilizes current phase variation with respect to input voltage at a resonant frequency which is obtained at aligned rotor position. Each phase circuit consists of an external sampling resistance, R, motor phase inductance, L (θ), and an external capacitance, C which are fed by an external sinusoidal voltage having the aligned resonant frequency. Of course, there are two different selections for the resonant frequency namely, aligned or un-aligned rotor position inductances which can be used. The current flowing through the resistor has the same frequency as the input voltage which is the resonant frequency but it can have different phase shift when compared to the input voltage due to the variation of phase inductance, L (θ) which is directly proportional to rotor position. At resonant frequency the variations are large therefore; the produced resistor voltage waveform compared to the input sinusoidal voltage waveform can produce a pulse width proportional to the position of the rotor. The width of the pulse is determined accordance to the phase inductance value which is directly proportional to the rotor position. In this paper aligned position inductance is employed for the detection of rotor position. Finally, the paper presents the results obtained which demonstrates the feasibility and practicability of the method and outlines the advantages of this technique.