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---
readstatus: false
dateread:
title: "Feedback Control Theory"
year: 2009
authors:
- "Doyle, John"
- "A, Francis"
- "Tannenbaum, Allen"
citekey: "doyleFeedbackControlTheory2009"
---
# Indexing Information
## DOI
[](https://doi.org/)
## ISBN
[](https://www.isbnsearch.org/isbn/)
## Tags:
>[!Abstract]
>In any system, if there exists a linear relationship between two variables, then it is said that it is a linear system.
>[!note] Markdown Notes
>None!
# Annotations
>[!attention] Highlight
> *The book is addressed to students in engineering who have had an undergraduate course insignals and systems, including an introduction to frequency-domain methods of analyzing feedbackcontrol systems, namely, Bode plots and the Nyquist criterion.*
>
>[!attention] Highlight
> *The simplest objective might be to keep y small(or close to some equilibrium point)—a regulator problem—or to keep y r small for r, a referenceor command signal, in some set—a servomechanism or servo problem.*
>
>[!attention] Highlight
> *Uncertainty arises from twosources: unknown or unpredictable inputs (disturbance, noise, etc.) and unpredictable dynamics.*
>
>[!attention] Highlight
> *Ideally, the model should cover the data in the sense that it should be capable of producingevery experimentally observed input-output pair. (Of course, it would be better to cover not just the data observed in a finite number of experiments, but anything that can be produced by the realphysical system. Obviously, this is impossible.)*
>
>[!attention] Highlight
> *Very rarely is the exogenous input w a fixed, known signal. One of these rare instances is wherea robot manipulator is required to trace out a definite path, as in welding. Usually, w is not fixed but belongs to a set that can be characterized to some degree. Some examples:• In a thermostat-controlled temperature regulator for a house, the reference signal is alwayspiecewise constant: at certain times during the day the thermostat is set to a new value. The temperature of the outside air is not piecewise constant but varies slowly within bounds.• In a vehicle such as an airplane or ship the pilots commands on the steering wheel, throttle, pedals, and so on come from a predictable set, and the gusts and wave motions have amplitudesand frequencies that can be bounded with some degree of confidence. • The load power drawn on an electric power system has predictable characteristics.Sometimes the designer does not attempt to model the exogenous inputs.*
>
>[!attention] Highlight
> *transfer function fromreference input r to tracking error e is denoted S, the sensitivity function*
>
>[!attention] Highlight
> *Lemma 1 The 2-norm of Gˆ is finite iff Gˆ is strictly proper and has no poles on the imaginaryaxis; the ∞-norm is finite iff Gˆ is proper and has no poles on the imaginary axis.*
>
>[!attention] Highlight
> *A stronger notion of well-posedness that makes sense when P, C, and F are proper is thatthe nine transfer functions above are proper. A necessary and sufficient condition for this is that1 + PCF not be strictly proper [i.e., PCF(∞) 6= 1].*
>
>[!attention] Highlight
> *Nyquist Criterion Construct the Nyquist plot of PCF, indenting to the left around poles on the imaginary axis. Let n denote the total number of poles of P, C, and F in Res ≥ 0. Then the feedbacksystem is internally stable iff the Nyquist plot does not pass through the point -1 and encircles itexactly n times counterclockwise.*
>
>[!attention] Highlight
> *Define the loop transfer function Lˆ := PˆCˆ. The transfer function from reference input r totracking error e isSˆ :=11 + Lˆ ,called the sensitivity function—*
>
>[!quote] Other Highlight
> *Here we used Table 2.1: the maximum amplitude of e equals the ∞-norm of the transfer function. Or if we define the (trivial, in this case) weighting function W1(s) = 1/ǫ, then the performance specification is kW1Sk∞ < 1.The situation becomes mo*
>
> >[!note] Note
> >Ladies and gentlemen, we got him.
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# Chapter 1:

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## Where did Robust Control come from? ## Where did Robust Control come from?
After the beginnings of modern control and the development of optimal control, John Doyle released a paper in 1978 titled [Guaranteed Margins for LQG regulators](doyleGuaranteedMarginsLQG1978a). This is a less than one page paper that basically gave birth to the robust control field, with a three word abstract: "There are none." I'm working out the kinks in this one ([[Basic Feedback Control]]), but essentially the gaussian part of the LQG is what destroys the guaranteed part of the phase and gain margins. The additional estimator involved can really screw with things. After the beginnings of modern control and the development of optimal control, John Doyle released a paper in 1978 titled [Guaranteed Margins for LQG regulators](doyleGuaranteedMarginsLQG1978a). This is a less than one page paper that basically gave birth to the robust control field, with a three word abstract: "There are none." I'm working out the kinks in this one ([[Basic Feedback Control]]), but essentially the gaussian part of the LQG is what destroys the guaranteed part of the phase and gain margins. The additional estimator involved can really screw with things.
I should add some context: [[4 Qualifying Exam/3 Notes/Feedback Control Theory]].
# What does Robust Control do? # What does Robust Control do?
Robust control works with Robust control works with
[[What is gain scheduling?]] [[What is gain scheduling?]]