An Approach for Improving Performance of Sensorless Field Control

Abstract

Sensorless vector control is preferred in some applications, because there is no need for speed or position sensor. However, by their very nature, they are susceptible to making position error in rotor position estimation. As a consequence the performance of motor drives employing this technology is lower than those which employ sensors. This paper presents a new approach which identifies and uses rotor slot harmonic current component in the stator current to identify rotor position. The time taken by the algorithm used is short enough to be embedded within the vector control algorithm. The essence of the algorithm is treating the current component due to rotor slot harmonics as an amplitude modulated signal on the fundamental current component. The magnitude of this current component is identified via demodulation. Using this information rotor position and speed can be determined. This approach is tested on a commercial induction motor and some results are presented which illustrate that rotor position can be successfully determined.