Reference processing in Two-Degree-Of-Freedom Control: Separation, Independence or Optimality

This communication deals with the realization of a two-degree-of-freedom (2-DOF) compensator. The well known properties and advantages of such compensators are reviewed as well as different ways of realize them. The advantages of using a 2-DOF compensator are well known: the closed loop properties can be shaped independently of the reference tracking transfer function. This is why we can talk about separation and independence of properties: that depends on the kind of processing we apply to the reference signal. Depending on the design approach to be applied, separation could be preferred even independence seems to be desirable. What we analyze is the kind of reference processing that results from an optimization problem. It turns out that the optimal solution implies complete separation and independence. It turns out that the resulting optimal 2-DOF controller results to possess a concise structure that accounts for a complete separation of the reference properties and a complete independence of the feedback controller