Composition of frequency responses and robust stability for multi-loop control system with model uncertainty

In this paper, we describe a graphical method of composing frequency responses for cascade connected plants of control system with model uncertainty and the robust stability of feedback control for such systems, i.e., multiloop control systems. The composition of frequency responses is represented sequentially by a recurrent inequality, and the evaluation of the robust stability is expressed by a series of inequalities provided in the reduction process of the block diagram. A computer-aided system for control system design is constructed on a workstation by using the C language.