An Approach for Improving Performance of Sensorless Vector Control

Sensorless vector control methods are preferred in some applications because of lack of position or speed sensor. However, such approaches are prone to error in prediction of rotor magnetic field position. As a consequence, sensorless vector controlled motors have inferior performance as compared to methods, which employ a sensor. The approach in this paper presents a method, which allows prediction of the magnitude of the rotor slot harmonics embedded in motor current, in a duration so short that they can be computed in the period in which vector control algorithm references are calculated. The essence of the presented approach is recogniton of the fact that the fundamental component of motor current actually is amplitude modulated by a current component at rotor slot harmonic frequency. Using this information, rotor position or motor speed can be obtained. The method developed for this purpose is described and tested on a motor in the laboratory and the results obtained are presented