New input-to-state stability conditions of linear systems with interval time-varying delays and their application to power systems

It is commonly believed that the Lyapunov-Krasovskii functional method plays an important role in obtaining input-to-state stability conditions of systems with interval time-varying delays. For a system with an interval time-varying delay, an appropriate functional should be constructed during applying the method. Nevertheless, the delay has an interesting property that the delay in different delay intervals can have varying impacts on the system. In a way, the property is not considered adequately for the Lyapunov-Krasovskii functional method, which may give rise to conservative conditions. This article proposes a new input-to-state stability analysis method by taking advantage of the ignored property. When the new method is adopted, multiple functionals are constructed for the delay in the different delay intervals. This means that the multiple functionals method is more applicable in practice than the Lyapunov-Krasovskii functional method. With the help of the proposed method, new input-to-state stability conditions for linear delay systems are derived. A numerical example is presented to show that the obtained conditions are effective. At last, the newly derived conditions are applied to power systems with delayed load frequency control schemes.