Fuzzy IMC for Unstable Systems with Time Delay

Open-loop unstable systems with time delay are difficult to control using routine control methods. To solve this problem, an improved internal model control scheme, which adds a PD controller to traditional IMC structure, is proposed. Set point tracking performance and robustness can be designed independently. The tuning formula of PD controller is confirmed by a new performance index function. Fuzzy self-tuning rules of the filter time constant are built for the time-varying system. can be modified in real time in order to improved the closed-loop response performance. Simulations show that the improved IMC method is not only effective for the dynamics and the stability of control system but also effective for the process robustness. In addition, the proposed method is easy to design and regulate, and it is fit for engineering application.