Output control of MIMO system with unmatched disturbance based on high-order unknown input observer

In this paper, the output control for a general MIMO linear system subjected to unmatched disturbance is considered. A smooth backstepping control law is developed under the assumption that the state and disturbance as well as its derivatives are known firstly. Then in order to estimate the required information, a high-order unknown input observer (HOUIO) is developed, and it is proven that based on the estimation by such the HOUIO, the designed controller can compensate all the disturbances from output channels and asymptotically drive the output to zero. Comparing with the traditional sliding mode control laws, the control law we design does not contain any switching function, so it can effectively reduce the chattering. Finally, simulation results are given to show the effectiveness of our methods.