Output stabilization of the system with mismatched uncertainties using higher order sliding mode approach

The paper deals with the output stabilization of the system in the presence of unmatched uncertainties using higher order sliding mode control. Super twisting control is used to achieve second order sliding mode on the defined sliding surface. Here a sliding surface is proposed based on the information of output and observed states. Higher order sliding mode observer (HOSMO) is used to observe the states of the system. The gains of the observer are chosen in such a way that the output error goes to zero very fast before the sliding mode is enforced into the system. During this the HOSMO estimates the unmatched disturbance exactly. It is shown that once the sliding mode is established thereafter the reduced order dynamics is unaffected by unmatched uncertainties. The performance of the proposed technique is validated in the simulation and the results are very promising.