Robust Sensorless Scalar Control of Induction Motor Drives with Torque Capability Enhancement at Low Speeds

In this paper, a new sensorless scalar control capable of enhancing torque capability for induction motor drives at low speeds is proposed. The proposed control addressed the problem that the conventional volt-per-hertz (V/f)control suffers from: torque capability is significantly impaired at low speeds due to stator flux weakening. A simple, encoder-free, but robust voltage compensation scheme for stator flux strengthening is therefore developed based on the dynamic model of an induction machine. Both simulation and experimental results are provided to demonstrate the superiority of proposed sensorless scalar control in torque capability enhancement and speed regulation over open-loop V/f, as well as stator resistive voltage compensated V/f control, especially at low speeds.