Robust tuning of PI and PID controllers: using derivative action despite sensor noise

This article presents some easily understood and applied methods for close-to-optimal tuning PI and PID controllers. By optimal it means good midfrequency robustness and the best possible tradeoff between output performance and control activity. For plants with all poles on the negative real axis, a simple step response can provide adequate plant knowledge. For plants with integral action, an impulse response or a relay experiment can be used. In all PID cases, the controller zeros can be fixed, the control activity can be varied by the filter factor, and, finally, the integral gain can be adjusted to the required damping of a step response for the closed-loop system. with this strategy, tuning a PID controller is as easy as tuning a PI controller, the difference being that the PID solution gives additional freedom for selecting slightly higher control activity which significantly improves the output performance. When the situation demands HF rolloff of the controller, the PI or PID controller can be augmented by an additional lowpass filter. In these cases, the inclusion of derivative action is recommended. Four of the five controller parameters are then easily found, and the remaining gain can be manually tuned to obtain a desired tradeoff between output performance and damping (MF robustness).