Robust control for input time-delay systems: A disturbance observer approach

Time-delay control problem for the system with an integrator becomes especially difficult when the disturbance input is a time-varying signal. This paper presents a nonminimum phase disturbance observer (DOB) approach to design a robust controller for input time-delay systems with time-varying disturbances. Position control problem for a simple pendulum system with input time-delay has been considered to test the effectiveness of the proposed control method. The effect of the time-varying disturbance owing to the load mass uncertainty has been alleviated by using a non-minimum phase DOB together with the Smith predictor (SP). In comparative computer simulations we have considered the uncertainties for the delay time λ as well as the load mass M of the system. Simulation results show the robust performance of the proposed method against the system uncertainties.