A comparison between Internal Model Control, optimal PIDF and robust controllers for unstable flow in risers

Anti-slug control of multiphase risers involves stabilizing an open-loop unstable operating point. PID control is the preferred choice in the industry, but appropriate tuning is required for robustness. In this paper, we define PIDF as a PID with a low-pass filter on its derivative action where the low-pass filter is crucial for the dynamics. We compared a new PIDF tuning based on Internal Model Control (IMC), together with two other tunings from the literature, with an optimal PIDF controller. The optimal PIDF tuning was found by minimizing a performance cost function while satisfying robustness requirements (input usage and complementary sensitivity peak). Next, we considered two types of robust H∞ controller (mixed-sensitivity and loop-shaping). We compared the controllers based on their pareto-optimality, and we tested the controllers experimentally. We found that the new IMCPIDF controllers is the closest to the optimal PIDF controller, but the robustness can be further improved by H∞ loop-shaping.