Sensorless induction motor drives

The desirability of eliminating mechanical shaft sensors for induction motor drives has led many manufacturers to include sensorless vector drives to their product range. However, current generation sensorless drives are unable to exhibit the same performance as sensored vector drives, particularly at frequencies below a few Hz. This paper reviews current methods and research that may expand the application of sensorless drives into areas that currently require speed sensors. The emphasis of the review is on low speed performance and the inherent problems of model-observer based methods are discussed. In order to overcome these problems, nonmodel based methods relying on the tracking of induction machine saliencies are reviewed.