Control of unstable non-minimum-phase delayed systems

The control of systems with long delays, by considering the option of stable/unstable and minimum/non-minimum-phase processes, is a challenging one. Most of the existing solutions do not cover all the situations and, in any case, they lead to complex controllers. Simple controllers, easy to design and tune, are very important in the process industry. In this paper, some control schemes based on a new but very simple Smith Predictor are presented, the tuning of the controllers being done on a delay-free model. Internal stability and robust stability analysis for these control structures is provided. Several illustrative examples taken from previous works are included to demonstrate the simplicity and superiority of the proposed method over those already published both for robust stability and to reject load disturbance.