Two-Degree-of-Freedom PID Tuning Based on an Uncertainty and Disturbance Estimator *

In this paper, a simple tuning method for two-degree-of-freedom (2DOF) PIDs is presented. The proposed methodology is based on an uncertainty and disturbance estimator. This model-based technique allows decoupling of the tracking and disturbance rejection performances. It is shown how, for second-order systems and with appropriate adjustments, an equivalent 2DOF PID controller can be obtained. The 2DOF PID parameters are then easily tuned to meet the desired tracking performance by specifying a reference model. Furthermore, one single parameter can be adjusted online to obtain a trade-off between disturbance rejection and robustness in each particular application. The proposed method is tested in a wide range of plants, including unstable first-order systems with time delay. Two comparisons with well-known tuning methods are performed.