This paper considers the problem of fixed-time stability (FTS) for switched nonlinear time-varying (NTV) systems. Firstly, three sufficient conditions are proposed to verify the FTS of NTV systems by using the improved Lyapunov function, which has a tighter upper bound of time derivative. Then, two FTS conditions are given for the switched NTV system by extending the obtained results, moreover, a switching strategy is also provided by using the minimum dwell time method. Finally, the obtained results are extended to study the FTS of impulsive NTV systems. Comparing with the existing results, the obtained conditions have two improvements: (1) provides a more accurate estimate for the upper bound of settling time of NTV systems, and (2) allows the Lyapunov function to increase at the switching instant of switched NTV (or impulsive NTV) systems. Two numerical examples are given to illustrate the theoretical results.

本文考虑了切换非线性时变（NTV）系统的固定时间稳定性（FTS）问题。首先，通过改进的Lyapunov函数，提出了三个充分的条件来验证NTV系统的FTS，该函数具有更严格的时间导数上限。然后，通过扩展获得的结果，为交换式NTV系统提供了两个FTS条件，此外，还使用最小停留时间方法提供了一种交换策略。最后，将所得结果扩展到研究脉冲NTV系统的FTS。与现有结果相比，获得的条件有两个改进：（1）提供了更精确的NTV系统建立时间上限的估计，以及（2）允许Lyapunov函数在已切换NTV的切换瞬间增加（或脉冲NTV）系统。