Stability analysis and design guidelines for a speed-sensorless induction motor drive

In this paper, the authors propose a novel stability analysis for induction motor drive speed sensorless vector control systems based on the parametric approach which results in the analytical necessary conditions for stability. It is pointed out that the system can be unstable in the low-speed region with regenerative load. Assigning an appropriate feedback gain of the flux observer, however, can render stability and reduce the unstable region. As a guideline for designing the adaptive PI gain, it is shown that the integral gain determines the tracking speed of the estimates during acceleration/deceleration while the sensitivity to current measurement noises depends on the proportional gain. In addition, to avoid an oscillation in the speed estimator, a suitable corner frequency of the adaptive PI gain is required as a design trade-off.