Chapter 4. Two-Degree of Freedom Internal Model Control

Objectives of the Chapter

  • Introduce the two-degree of freedom (2DF) IMC system and elucidate its advantages over 1DF IMC when step disturbances enter through process lags.

  • Provide design methods for 2DF IMC systems with perfect models that give the best possible performance consistent with noisy measurements for inherently stable and inherently unstable processes.

Prerequisite Reading

Chapter 3, “One-Degree of Freedom Internal Model Control”


The IMC design methods presented in Chapter 3 assume that step disturbances enter into the process output without passing through the process (i.e., pd(s) = 1) in Figure 3.1, which is reproduced in Figure 4.1.

Figure 4.1. The 1DF IMC block diagram ...

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