Joint design method based on factorized representation of plant and controller of 2DOF control system

In many cases, control system synthesis is formulated as minimization of prescribed closed loop performance reflecting control requirements. Since the closed loop performance is a function of a controlled plant and a controller, a model identification and a controller design must interact with each other. This motivates us to consider the model identification and the controller design simultaneously. However, most of the previous joint design methods are not applicable to unstable plants because the identified plant model is usually used as the design parameter, i.e, a weighting function in the controller design. On the other hand, we have analyzed the internal structure of 2DOF control system using a coprime factorization on RH, and showm that two free parameters, K and Q epsilon RHinfinity, specify the tracking performance and the feedback performance, respectively. Also Tay et.al have proposed a parameterization of the plant dynamics by switching the role of the controlled plant and the controller, and introduced a free parameter R epsilon RHinfinity. In this paper, we propose a new joint design strategy based on the identification of R and the design, of Q. Since the identified plant parameter R is always stable, the proposed joint design strategy can be applied to a wider class than (including unstable plants) the conventional joint design method. Finally, the usefulness of the proposed method is verified by some simulations.