Feedforward based two degrees of freedom formulation of the Virtual Reference Feedback Tuning approach

This paper proposes the formulation of the Virtual Reference Feedback Tuning (VRFT) Method, on a feedforward based Two-Degree-Of-Freedom (2-DoF) control configuration. One implicit drawback of the original 2-DoF VRFT proposal is that the controllers are not independent between them, so a compromise arises when trying to solve the sensitivity shaping and the complementary sensitivity shaping at the same time. Instead, this paper proposes the use of an alternative 2-DoF that stands for a complete separation of the tracking and sensitivity problems, therefore allowing to face the problem by using two separate optimization problems. The sensitivity shaping problem is solved by the feedback controller and the complementary sensitivity shaping problem is solved with a feedforward controller. It is shown that with this configuration, the VRFT method can be successfully applied with the advantage of having two independent optimization problems for both targets.