Pass band and high frequency robustness for PID control

A procedure for fair comparison between different control structures and design parameters is suggested. Low, high and mid-frequency properties are then treated separately in the evaluation of closed loop performance and robustness. By this separation it is possible to investigate, for example, the trade-off between low frequency performance and high frequency robustness, while pass band robustness (stability margins) is kept constant. More specifically we consider tuning of PID controllers, and find as a result of our design and evaluation procedure that low frequency performance and closed loop bandwidth can be improved significantly, without losing high frequency robustness and mid-frequency stability margins. The key is to choose some parameters of a standard PID controller in a somewhat unconventional way.