A globally stable adaptive second order sliding mode control scheme for sensorless current-fed induction motors

The design of a globally stable second order sliding mode controller for sensorless induction motors is discussed in this paper. The adaptive component of the controller enables to compensate for the variation in time of the rotor resistance value, while the use of a suitably designed sliding mode speed/flux observer avoids the necessity of including speed and flux sensors within the control loop, making this proposal suitable for sensorless applications. The use of a second order sliding mode control approach, realized by regarding the second time derivatives of the stator currents as discontinuous auxiliary control inputs, is effective in limiting the mechanical wear, making this proposal more acceptable in practical applications than those based on conventional sliding mode control.