Disturbance/Uncertainty Estimator Based Robust Control of Nonminimum Phase Systems

An open problem in disturbance/uncertainty estimator based control is to obtain explicit mathematical expressions for robust stability, performance, and bandwidth requirement. This paper offers a path based on $\mathcal {H}_\infty$ robust control to resolve this problem. Robust stability/performance is assured at the design phase. The main controller and disturbance observer are handled as a whole. The ideas are applicable to nonminimum phase systems as well. The theory is verified experimentally on a pan-tilt system and numerically on a rotary mechanical system. Comparisons with state-of-the art methods in literature show noticeable performance and robustness improvements.