LAUSR

This paper analyses the stability problem of linear systems with interval time-varying delay. In regard to the delay, it has the lower and upper bounds and its derivative is unknown or itself is not differentiable. First of all, it is the first time that the delay-related triple integral terms are used to construct the augmented Lyapunov–Krasovskii functional (LKF) and the delay-related integral quadratic terms are estimated by the third-order free-matrix-based integral inequalities (TFIIs). Then, based on the same LKF and same TFIIs and by introducing two sets of state vectors, the derivative of the LKF is presented as the quadratic and quintic polynomials about the delay respectively. Next, for the quadratic and quintic polynomials, new negative definite conditions (NDCs) are provided to form the linear matrix inequality (LMI) conditions. Finally, the advantages of these two criteria are checked through some classical numerical examples.