Robust Output-Feedback Control by Simultaneous Estimation of System State and Disturbance Input

This paper investigates a robust output-feedback control scheme for a class of vehicle systems, which is obtained by combining uncertainty and disturbance estimator (UDE) and Lunberger state observer (LSO) techniques. Two important features of the scheme are: (1) a compensation signal generated by a properly designed UDE is included in both the LSO and controller to reject input disturbances; (2) a new parameter mapping is introduced for parameter tuning to obtain small steady-state errors. The parameter conditions that ensure the closed-loop system is input-to-state stable is identified. We find from the condition that: owing to the coupling between the LSO and UDE, the parameter set for the LSO with disturbance compensation is larger than that for the LSO without disturbance compensation. Both numerical simulation and experimental results arc presented to demonstrate the effectiveness of the scheme and the main finding of the paper.