Input-output stability of interconnected systems

New results for input-output stability of multiple input-multiple output systems, viewed as interconnected systems, are established. In the present approach, which can also be utilized in stabilization and compensation procedures, large-scale systems are analyzed in terms of their subsystems and interconnecting structure. The method advanced is applied to a specific example. The present results differ appreciably from earlier ones by Porter and Michel because they are applicable to a larger class of problems, they are simpler to apply when conicity conditions are used, and in addition to circle criteria, they also utilize Popov-type conditions. The present procedure differs significantly from existing methods concerned with the analysis of systems having several nonlinearities. Many of these earlier results (multidimensional Popov criteria) usually involve frequency dependent test matrices and graphical frequency domain interpretations are generally not possible. The present results require frequency independent test matrices and yield graphical frequency domain interpretations.