Stable operation of adaptive observer based sensorless induction motor drives in regenerating mode at low speeds

Sensorless induction motor drives can be divided into two groups. One is based on fundamental components. The other is based on high frequency components injection. The latter may operate stably under zero frequency, which occurs in regenerating mode at low speeds. It, however, causes loss increasing and torque ripple. The former is difficult to operate under zero frequency. The authors propose a stable method categorized in the former group even in regenerating mode at low speeds. The proposed method is based on an adaptive flux observer. First, a new observer gain design is shown. Next, a method avoiding zero frequency operation with controlling a rotor flux level is proposed.