The challenges of achieving stability and good damping of a sensorless induction motor drive are much greater than for a sensored drive. In this paper, some frequently proposed flux and speed estimators—such as reduced- and full-order observers—are reviewed, along with their key static and dynamic properties as well as their parameter sensitivities. Three commonly occurring instability phenomena and their remedies are discussed, along with suitable analysis methods. Low-speed instabilities are most severe, and therefore, the stator resistance is the single most critical parameter. Methods for reducing the impact of this parameter are discussed.
