A speed-sensorless IM drive with decoupling control and stability analysis of speed estimation

A new sensorless drive based on a decoupling control and an adaptive full-order observer is developed. A modified decoupling control is introduced and integrated with the adaptive observer to reduce the complexity of the whole system. The speed estimation based on adaptive control theory is analyzed and the necessary and sufficient conditions for stability of the speed estimation are analytically derived. It is indicated that the system can be unstable in the low-speed region with regenerative loads. However, assigning an appropriate feedback gain to the adaptive observer can restore the stability and reduce the unstable region. Sensitivity of the sensorless drive against parameter and measurement errors is also qualitatively discussed. Simulation and experimental results are then given to verify the validity of the theoretical results