Chapter 10. Cascade and Feed-Forward Control

The objective of this chapter is to develop feed-forward- and cascade-control system design procedures. The emphasis of both of these strategies is on rejecting disturbances. After studying this chapter, the reader should be able to do the following:

• Given an instrumentation diagram for a cascade-control strategy, develop the corresponding control block diagram using either a series or parallel structure

• Tune cascade controllers; tune the secondary loop first; then tune the primary controller with the secondary loop closed

• Given an instrumentation diagram for feed-forward/feedback control, develop the corresponding control block diagram

• Develop the closed-loop transfer functions for feed-forward/feedback control

• Design feed-forward/feedback controllers. Understand physical realizability limitations due to time delays and RHP zeros

The major sections of this chapter are as follows:

10.1 Background

10.2 Introduction to Cascade Control

10.3 Cascade-Control Analysis

10.4 Cascade-Control Design

10.5 Cascade IMC

10.6 Feed-Forward Control

10.7 Feed-Forward Controller Design

10.8 Feed-Forward Control in the IMC Structure

10.9 Summary of Feed-Forward Control

10.10 Combined Feed-Forward and Cascade

10.11 Summary