研究了一类具有动态领导者并且存在时变耦合时滞的多主体系统的一致性问题．在所考虑的
模型中，领导者的速度不能被精确量测．为了跟踪这样一个领导者主体，将对每个跟随者主体构造分散式状态估计器以及设计基于邻居的控制器；同时，由于耦合时滞的存在，基于邻居的控制器和状态估计器均包含了时变时滞的作用．当多主体系统的耦合拓扑是固定的或切换的有向图时，跟随者与领导者之间的跟踪误差得到了估计．特别地，可以证明，当动态领导者的速度可以被精确量测时，每一个跟随者都能够跟踪上领导者．

This paper considers the consensus problem of multi-agent systems with an active leader and time-varying delay. In our problem, the velocity of the leader can not be measured precisely. To track such a leader, a decentralized state-estimation rule is constructed for each agent, which is used to design local controllers. Due to the interconnection delays, both neighbor-based control rules and stat-estimation rules involve time-varying delays. Moreover, with the directed (fixed or variable) interconnection topologies described by digraphs, the leader-following errors are estimated. Particularly, it is proved that each agent can track the leader if th input of the active leader is precisely known.