Simple PID tuning rules for varying time-delay systems

This paper discusses tuning of PID controllers for varying time-delay systems. We analyze the properties of the AMIGO tuning rules of Astrom and Hagglund applied to varying time-delay systems and propose improved tuning rules which increase the robustness to delay variations at the expense of a small degradation in nominal performance. We suggest a tuning scheme that uses the simple AMIGO tuning on an extended plant, and define the design concepts for extending the plant. This approach allows treating the maximum time-delay as a design parameter for the tuning rules. The proposed tuning rules are compared via simulations.