Virtual Reference Feedback Tuning for non minimum phase plants

Model Reference control design methods fail when the plant has one or more non minimum phase zeros that are not included in the reference model, leading possibly to an unstable closed loop. This is a very serious problem for data-based control design methods where the plant is typically unknown. For Iterative Feedback Tuning a procedure was proposed in [1] to overcome this difficulty. In this paper we extend this idea to Virtual Reference Feedback Tuning, another data-based control design method. We present a simple two-step procedure that can cope with the situation where the unknown plant may or may not have non minimum phase zeros.