Two-step design of critical control systems for non-minimum phase plants

A two-step design of critical control systems is proposed based on the principle matching. The plant is assumed to be a non-minimum phase system. The controller structure is chosen as a Davison type integral controller with an observer. In the first step, a critical control system is designed on the assumption that the state of the minimum phase part can be used for the feedback. A quadratic performance index with tunable parameters is used as a tool for determining the partial state feedback gain matrix. The second step determines the observer gain matrix such that the output feedback controller performs as in the partial state feedback controller obtained in the first step. The formal partial LTR procedure using a Riccati equation is adopted for this purpose. The numerical search required in each step is simpler compared with the conventional approach based on the principle of matching. An illustrative design example is presented.