Observability-Index-Based Control Strategy for Induction Machine Sensorless Drive at Low Speed

This paper focuses on the observer-based methods for induction machine sensorless drive. It is well known that the use of speed observer is limited at a very low stator frequency due to speed unobservability. Some existing methods propose to avoid the zero-stator-frequency working points. These methods are nonetheless limited to high-torque operations. The first contribution of this paper is to analyze finely the speed observability, which leads...