Stability analysis of speed adaptive flux observer for induction motor speed sensorless vector control

Stability analysis of speed adaptive flux observer for induction motor speed sensorless vector control, which is always unstable in the regenerating mode at low speeds, is performed by applying Routh-Hurwitz criteria to the small signal linearized model of IM. Based on the analysis, a modified speed adaptation law is proposed. The speed accuracy could be greatly improved by adding the magnetizing current estimation error to the general speed estimation law, and the instability behavior in the low speed regenerating mode could be remedied by adjusting the adaptation gain on-line. At last the validity of the proposed scheme is verified by the experimental results of speed sensorless field-oriented vector controlled 7.5kW induction motor platform.