Abstract:

In chemical plants and industrial plants, there are problems of uncontrollable first-order time-delay unstable system. In view of this problem, an improved scheme of two-degree-of-freedom controller is proposed in this study. The main idea of the improved scheme is to change the disturbance controller to the PID controller form with leading lag filter while keeping the controller form and algorithm of the set value tracking controller in the original scheme unchanged. Meanwhile, the parameters are tuned based on the direct synthesis method. Finally, the parameter value is selected in accordance with the best compromise between robust stability and load rejection performance. The simulation results show that the proposed scheme significantly improves the system performance and robust stability compared with other schemes. In addition, applying this solution to an isothermal chemical reactor in Example 2 also obtaines satisfactory results.

Key words: first order unstable system with time delay, set point tracking controller, disturbance controller, direct synthesis method, maximum sensitivity function, robust stability, the system performance