MATLAB CONTROL SYSTEM TOOLBOX 9 Spezifikationen PDF herunterladen (Seite 35)

100

101

Creating LTI Models

2-17

Frequency Response Data (FRD) Models

Insomeinstances, you may only have sampled frequency responsedata, rather

than a transfer function or state-space model for the system you want to

analyze or control. For information on frequency response analysis of linear

systems, see Chapter 8 of [1].

Forexample,suppose the frequencyresponse functionfortheSISOsystem you

want to model is G(w). Suppose, in addition, that you perform an experiment

to evaluateG(w)at a fixed set of frequencies, . You can do this by

drivingthesystem with a sequenceof sinusoids at each of these frequencies,as

depicted below.

Here is the input frequency of each sinusoid, i =1...n,andG(w) =

. The steady state output response of this system satisfies

A frequency response data (FRD) object is a model form you can use to store

frequency response data (complex frequency response, along with a

corresponding vector of frequency points) that you obtain either through

simulations or experimentally. In this example, the frequency response data is

obtained from the set of response pairs: .

Once you store your data in an FRD model, you can treat it as an LTI model,

andmanipulateanFRDmodelinmostofthesamewaysyoumanipulateTF,

SS, and ZPK models.

The basic syntax for creating a SISO FRD model is

sys = frd(response,frequencies,units)

where

•

frequencies is a real vector of length Nf.

…

,,,

tsin

G(w) =

()

jGw

()∠()

exp

()

tGw

()∠

()

i;sin 1

…

n==

()

(,){}

…

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