Speed sensorless torque and flux control of induction motor

Due to its rigidness, maintenance free operation and many other advantages, the squirrel cage induction motor is the most widely used electrical motor in industrial applications. However, due to its highly coupled nonlinear structure it has certain limitations in sensorless applications in servodrives. This is due to the fact that the currently used control schemes like field oriented or direct torque control, errors occur due to the parameters variation, integral drift and noise. Those errors can be overcome with the use of the advanced parameter estimators and observers, however the speed sensorless operation, especially in the low speed region still presents a problem. Novel induction motor speed sensorless torque control is proposed. The control is quite different than the conventional field-oriented or direct torque control. First, the produced torque is explicitly continuous output variable of control. Second, a new rotor flux observer, which allows speed sensorless operation of IM by low and zero speed, was developed. A new stator and rotor flux controller/observer based on continuous sliding mode and Lyapunov theory are developed. The reference tracking performance of torque and rotor flux is demonstrated in series of transient characteristics by simulation and experimental results.