PID control with robust disturbance feedback control

Disturbance Feedback Control (DFC) is a technique, originally proposed by Fuji Electric, for augmenting existing control systems with an extra feedback for attenuation of disturbances and model errors. In this work, we analyze the robustness and performance of a PID-based control system with DFC. A multiplicative uncertainty model is used to represent mismatch between a nominal model and the actual plant, and expressions for robust stability, nominal and robust performance are derived. We propose a simple grid-based search algorithm that can be used to find DFC gains to achieve robust stability and performance (if such gains exist). Finally, two different simulation case studies are evaluated and compared. Our numerical studies indicate that better performance can be achieved with the proposed method compared with a conservatively tuned PID controller and comparable performance can be achieved when compared with an H-infinity controller.