Robust disturbance attenuation with unknown input observer and sliding mode controller

For a linear system with mismatched disturbance, a robust sliding mode control algorithm using only output feedback is developed in this paper. Although the system with intrinsic issues of unknown input and nonminimum phase is inherited, an improved reduced-order unknown input observer is to be presented in estimating the state of the system. The manipulation of H-infinity control theory along with the implementation of estimated system state can result in robust stabilization with disturbance attenuation when designing integral sliding surface of a system in the sliding mode. A controller is also designed to satisfy the reaching and sliding condition in line with the estimated system state. Finally, a numerical example is explained for showing the applicability of the proposed scheme.