Stability analysis of composite systems

The stability of composite systems is investigated in terms of their subsystems and their interconnecting structure. Whereas previous investigators utilized vector Lyapunov functions in their approach, scalar functions consisting of weighted sums of scalar Lyapunov functions of subsystems of the composite systems are employed presently. It is shown that the scalar Lyapunov function approach may in general yield stability results which are less conservative than those obtained by the vector Lyapunov function approach. Both methods are applied to specific examples considered previously. These examples demonstrate the improvement of the present results.