A Smith-like control design for performance enhancement of systems with RHP zeros

Motivated by the common non-minimum phase property of dead time and right-half-plane (RHP) zero, this paper presents a Smith-like scheme for control of systems with RHP zeros. It is shown that RHP zeros and possible dead time can be removed from the characteristic equation of the scheme so that the control design is greatly simplified, and enhanced performance is achievable. By model reduction, a unified design with a single tuning parameter is presented for processes of different order. The relationships between the time domain specifications and the tuning parameter are developed to ease the design trade-off. Simulation examples are presented to demonstrate the effectiveness of the proposed scheme. For robustness, it is shown that our design ensures a gain margin of 2 and phase margin of π/3, as well as 100% perturbation of the RHP zero or uncertain time delay of ΔL ≤ τ/0.42.