Estimation of Rotor Position in a Three-Phase SRM at Standstill and Low Speeds

Switched reluctance motors (SRMs) are widely employed as industrial drives because they are inexpensive, simple, and sturdy, and further, they deliver a robust and reliable performance. SRMs are controlled with a rotor position sensor attached to the motor shaft. Normally, encoders, resolvers, or Hall sensors are used as position sensors. The use of these sensors, however, increases the size and cost of the machine and degrades its performance. Therefore, to overcome these difficulties, several sensorless drive techniques have been reported. This paper presents a method for estimating the position of a rotor in an SRM, based on calculation of the space vector of the phase inductance at standstill and low speeds. The position at standstill is obtained simply without making use of the magnetic characteristics of the motor or any additional hardware. Assuming the inductance waveform to be a sine wave, the position of the rotor at standstill is obtained from the phase inductance vectors of all phases. At low speeds, position estimation is carried out by applying a DC link voltage to the unenergized phases. The validity of the proposed method is experimentally verified. (C) 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(2): 55-63, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21205