Page - (000106) - in Control Theory Tutorial - Basic Concepts Illustrated by Software Examples

Chapter14 Summary Manyothercontrolapproachesandapplicationshavebeendeveloped(Baillieuland Samad2015).Thoseextensionsbuildon the foundational principles emphasized in this tutorial.Threekeyprinciples recur. 14.1 Feedback Thereare two, andonly two, reasons forusing feedback.Thefirst is to reduce theeffect of anyunmeasureddisturbancesactingonthesystem.Thesecondis toreducetheeffectofany uncertaintyabout systemsdynamics. —Vinnicombe(2001,p.xvii) Feedbackisunnecessary ifonehasacomplete,accuratemodelofsystemdynamics. With an accurate model, one can map any input to the desired output. A direct feedforwardopen loopdoes the job. However, unpredictableperturbationsoccur.Modelsofdynamics almost always incorrectly specify the trueunderlyingprocess. Correctingerrorsby feedbackprovides thesinglemostpowerfuldesignmethod. Natural systems that control biological function often use feedback. Human- engineeredsystems typicallycorrect errors through feedback. 14.2 RobustControl [H]owmuchdoweneedtoknowaboutasysteminorder todesignafeedbackcompensator that leaves theclosed loopbehaviour insensitive to thatwhichwedon’tknow? —Vinnicombe(2001,p.xvii) Robustnessmeans reduced sensitivity to disturbance ormodeling error. Feedback improves robustness.However, feedbackonlydescribesabroadapproach. ©TheAuthor(s)2018 S.A.Frank,ControlTheoryTutorial, SpringerBriefs inAppliedSciences andTechnology,https://doi.org/10.1007/978-3-319-91707-8_14 103