Servo/regulation tradeoff tuning of PID controllers with a robustness consideration

This paper analyzes optimal controller settings for controllers with PID structure. The analysis is conducted from the point of view of the operating mode (either servo or regulation mode) of the control loop and tuning mode of the controller. It is well known that, specially for optimization based settings, the performance of the control loop is defined in terms of the expected operating mode of the control loop. When the control system is not operating on the same operating mode as the controller was tuned the performance may exhibit very poor results. The performance degradation with respect of the optimal performance is defined and analyzed for settings based on ISE-like optimization criteria. Also the gain and phase margins that optimal tuning provides are analyzed. As a consequence, in order to get a minimal performance degradation (with respect to both operating modes) with also a minimal reduction of the gain margin, tradeoff tuning settings are proposed.