Frequency Response of Feedback Controllers

Before we give some examples of the design of feedback controllers in the frequency domain, it would 1m wise to show what the common P, PI, and PID controllers look like in the frequency domain. These will be the that we will add to the process to get the total openloop Bode plots of.  

Openloop and dosedbop Bode plots for a three-CSTR system. 

A proportional controller merely multiplies the magnitude of at every frequency by a constant. On a Bode plot, this means a proportional controller raises the log modulus curve by 20 logiQ decibels but has no effect on the phase-angle curve. See Fig. 13.13n. 

---