  This paper considers the leader-follower tracking control problem for linear
interconnected systems with undirected topology and linear dynamic coupling.
Interactions between the systems are treated as linear dynamic uncertainty and
are described in terms of integral quadratic constraints (IQCs). A
consensus-type tracking control protocol is proposed for each system based on
its state relative its neighbors. In addition a selected set of subsystems uses
for control their relative states with respect to the leader. Two methods are
proposed for the design of this control protocol. One method uses a coordinate
transformation to recast the protocol design problem as a decentralized robust
control problem for an auxiliary interconnected large scale system. Another
method is direct, it does not employ coordinate transformation; it also allows
for more general linear uncertain interactions. Using these methods, sufficient
conditions are obtained which guarantee that the system tracks the leader.
These conditions guarantee a suboptimal bound on the system consensus and
tracking performance. The proposed methods are compared using a simulation
example, and their effectiveness is discussed. Also, algorithms are proposed
for computing suboptimal controllers.
