시간 지연으로서의 미분

By approximating the designed output derivative feedback controller as delayed output measurement feedback controller, we can achieve diverse aspects of derivative controller, while reducing negative sides. Strength of this approach can be, in particular stabilizing some of non-minimum phase systems with only output measurements. However, to achieve such phenomenon, theoretically designed output derivative controller has to be order higher then the relative degree of the system, which emits in the first sight, irregular, necessary condition. In this paper, we will prove such necessary condition, and show by simulation how approximation can stabilize specific non-minimum phase system.