Sliding-mode observer for speed-sensorless induction motor drives

A sliding-mode observer for the speed-sensorless direct torque vector control of induction motors is proposed. The observer estimates the motor speed, the rotor flux, the angular position of the rotor flux and the motor torque from measured terminal voltages and currents. The use of the nonlinear sliding-mode technique provides very good performance for both low- and high-speed motor operation and robustness in motor losses and load variations. The proposed observer uses neither a PI controller nor complicated observer gains, thus establishing an easy setup for any type of motor. Also, the convergence of the proposed observer is examined using the Lyapunov theory. Experimental results using a TMS320F240 digital signal processor are presented for low-speed operation (5 Hz), full speed operation (50 Hz), and forward to reverse operation. Finally, the proposed observer is compared with other recently reported model-reference adaptive system techniques.