In this paper, we study consensus robustness and performance problems
for continuous-time multi-agent systems. We consider first-order
unstable agents interconnected by an undirected graph, coordinated by a
delayed output feedback protocol. Our objectives are twofold. First, we
seek to determine the largest range of delay permissible so that the
agents may achieve robustly consensus despite variation of the delay
length, herein referred to as the delay consensus margin. Second, we
attempt to determine consensus error performance quantified under an H 2
norm criterion, which measures the disruptive effect of random nodal
noises on consensus. For both problems, we obtain analytical solutions.
The explicit expressions provide conceptual insights and exhibit how the
agents' unstable pole, nonminimum phase zero, as well as the network
topology may limit fundamentally the consensus robustness and
performance.