Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001
· By adding extra feedback loops we can add levels of robustness to a control system.
· In this case the control loops appear to be nested.
· Consider a cascade control system for disturbances,
· Now consider a cascade controller for a multistage process, such as a sewage treatment plant with sequential tanks with varying flow rates. Here the disturbance would be the sewage flowing into the first tank. the two process blocks are the treatment tanks. The output is water returned to rivers The controllers vary the flow rates by looking at parameters for both tanks.
· To do design/analysis for these controllers we do an analysis of the innermost feedback loop. This then becomes a process, and we do design/analysis at the next higher loop.
· Select controllers for the system pictured below,
