Reference input tracking of inversion-based non-minimum phase system using adaptive two-degree-of-freedom control

Abstract

Reference input tracking plays a major role in control system Engineering. Inverse model technique is very useful for exact tracking of minimum phase system but for non-minimum phase system, it gives unbounded output response. This paper proposes an effective method for achieving the approximate desired trajectory tracking of unstable inversion-based non-minimum phase (NMP) system. Here two-degree-of-freedom control theory has been applied where feedback control is provided by arbitrary pole placement method to create the bounded response of unstable NMP system. Lyapunov based Direct Model Reference Adaptive Control (MRAC) of inverse transfer function model of NMP system act as feed-forward compensator in 2DOF framework to track the reference input trajectory. Unstable non-minimum phase plant can successfully track step, ramp and parabolic input signal with a minimum steady state error shown in the simulation results. Initial undershoot which is obvious in NMP system has been completely removed by this control strategy.