Two-degree-of-freedom output feedback controllers for discrete-time nonlinear systems

The control of nonlinear processes has attracted attention in the literature in recent years. Industrial applications of nonlinear methods have also been reported. An important class of nonlinear methods arise from geometric considerations. One method based on input/output linearizing state feedback is the model-state feedback structure. This structure results in a controller that is of minimal order, with one set of tunable parameters which directly shape the closed-loop input/output behavior. Moreover, this controller was shown to be a direct nonlinear analog of model-algorithmic control (MAC) . However, one limitation of the model-state feedback structure is the reliance on an open-loop observer. For continuous systems, a structure based on a closed loop nonlinear observer, but still retaining the desirable properties of the model-state feedback structure was developed previously. The goal of this work is to develop a similar structure for discrete-time nonlinear systems. In so doing, it will also be shown that the resulting nonlinear control structure also gives rise to a generalized model-algorithmic controller, which is not restricted by the condition of open-loop stability