Feedback control for plants with time delay

Abstract The paper considers the problem of feedback control design for plants with time delay. The role of the feedback is presented showing its ability to restrict the uncertainty in the plant model. The conditional feedback control structure is introduced and its properties for restricting model uncertainty are discussed. The presence of local feedback makes the conditional feedback structure pertinent for its usage when the plant contains a time delay element. The time delay model is replaced by its Pade series approximation. The key idea is to consider the time delay model as perturbation around its Pade series approximation. This fact allows utilizing the rational function expression in the procedure of controller design, thus avoiding using the irrational function of the time delay for this purpose. It is shown that the conditional feedback control structure gives an alternative than the Smith predictor method for controller design of plants with time delay e − θs in their structure. The efficiency of the presented method is demonstrated by a numerical example.