Appendix B. Review of Frequency Response Analysis


The objective of this appendix is to review the basic concepts behind frequency response analysis and its use in control system design. Topics discussed include

  • Bode and Nyquist plots.

  • Nyquist stability theorem.

  • Closed-loop response characteristics.

  • Controller performance and design criteria.


By frequency response we mean the response characteristics of the system when subject to sinusoidal inputs. The input frequency is varied, and the output characteristics are computed or represented as a function of the frequency. Frequency response analysis provides useful insights into stability and performance characteristics of the control system.

Figure B.1 shows the hypothetical experiment ...

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