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Ole Holm & Aron Butler:
"Robustness and Performance Analysis of PI and PID Controller Tunings"

Project report, NTNU, Nov. 1998.

Abstract:

A series of simulations has been carried out to compare the PI and PID controller tunings
of Skogestad with those of Cohen and Coon, Ziegler and Nichols, Aastrom et al., and Ho, et
al. for various process models. Using a simple feedback control loop, simulations of system
responses to setpoint changes and load disturbances were plotted and analyzed for speed of
response, stability, and robustness. It was concluded that Skogestad's tunings, although
they give a relatively slow response, were superior in stability and robustness in almost
all cases. In general his tunings gave a gain margin of around 3 and a phase margin of
approximately 50 degrees, while the others had on average gain margins around 2 and phase
margins 10 to 20 degrees lower than Skogestad's. Then several trials were made with
modifications to Skogestad's controller settings, and it was seen that slight improvements
in response speed could be achieved, but at the cost of decreased stability and robustness.