Robust design of PID controllers including auto-tuning rules

A new method for fair evaluation of different controllers has recently been proposed. Low, high and midfrequency properties are then treated separately in the evaluation of the closed loop performance and robustness. Experience from evaluation of parallel PID controllers has led to a set of simple rules for autotuning of stable non-oscillating processes. For this kind of plants serial PID controllers are also investigated, and it is shown that the best possible balance between low frequency performance and high frequency robustness is obtained by a double zero in the controller.