Speed sensorless torque tracking control of induction motor

A new control scheme of the torque trajectory-tracking controller for an induction motor is presented in the paper. The proposed approach addresses the problem of torque control of speed sensorless drives at both low and high speed, where rapid speed changes can occur. The scheme allows the precise and quick control of the induction motor flux and torque. A closed-loop rotor flux observer using sliding mode controller and a nonlinear stator frequency dependent gain is presented. Sliding mode controllers are used as the stator flux controller and in the rotor flux observer. Nonlinear stator frequency dependant gain used in the rotor flux observer enables the operation at low and high speed. Thus at low speed, the observer turns into the closed-loop observer using stator current, stator voltage and desired rotor flux values as inputs. At high speed the information from the desired rotor flux is disconnected and a classical voltage model is used. The reference tracking performance of torque and rotor flux is demonstrated in terms of transient and steady-state characteristics by simulation and experimental results.