Stabilizing method of speed adaptive flux observer for speed sensorless induction motor drives

Speed sensorless vector control induction motor drive systems adopting the speed adaptive flux observer usually suffer from an instability problem in the low speed regenerating mode. Stability analysis of the drive system at the steady state operating point was performed by applying the root-locus technique to the linearized model of the speed estimation system. Based on the analysis, an improved speed estimation method was proposed. The speed accuracy can be greatly improved by adding the magnetizing current error via an adaptation gain to the general speed adaptation law. The instability behavior in the low speed regenerating mode can be remedied by adjusting the adaptation gain on-line. The validity of the proposed scheme is verified by the experimental results.