Position estimation for sensorless control of synchronous reluctance motor at low speed using disturbance observer

Recently, synchronous reluctance motors (SynRMs) have attracted study because of their favorable properties, including limited thermal expansion of the shaft due to low heat generation by the rotor, the ability to drive at high velocity, a low degree of torque ripple and an absence of demagnetization problems. Sensorless control of SynRMs is now desired, and several methods have been proposed. These methods, however, have difficulties at low speed when the voltage signal necessary to estimate rotor position is very small. The authors have proposed a new position estimation method using high-frequency extended e.m.f. (EEMF) in which high-frequency voltage and current are calculated using a disturbance observer. Simulations have shown the new method to be very useful. In this paper it is shown, experimentally, that it is possible to drive the motor at low speeds with the coordinate transformation used the position θ̂ estimated by the new proposed method.