Multiple Signal Paths

Abstract

In many applications, the loop configurations considered so far are insufficient for achieving the design goals. Often, adding new signal paths in parallel with the initial path can help. Three useful arrangements are presented in this section. The formal equivalence between these arrangements is emphasized, and is used to derive a stability criterion useful for designing loops with almost-maximum gain. In order to make it easier to carry out a unified discussion of control configurations with multiple paths, Fig. 2.1 is modified as shown in Fig. 7.1 on p. 100. The change consists of renaming the gain blocks, selecting a case with zero reference (control) input and rotating the various elements around the loop. These changes do not have any effect on the open-loop gainL.Therefore, reference tracking and disturbance suppression, as well as stability properties are the same for all diagrams shown in Fig. 7.1 Diagrams like the bottom one in Fig. 7.1 will be used throughout this chapter.