Model reference robust control for SISO systems with unmatched disturbances

A new model reference robust control is proposed for single-input single-output (SISO) minimum-phase dynamical systems with unmatched disturbances, using only the input and output measurements. Based on VSS theory, an 'approximate differentiator' is proposed to estimate a special signal generated by the disturbance. By using the estimated special signal to cancel the influence generated by the disturbance, the intermediate input (a certain order filter of the input) is synthesized on the basis of the Diophantine equation to achieve the model reference purpose. Finally, the real control input is determined by employing the formulated 'approximate differentiator' technique. The output tracking error can be made arbitrarily small without the requirement for a large control energy to be available. Design examples and simulation results are presented to show the superiority and effectiveness of the proposed algorithm.