MATLAB: State observer bode plot

bode plotfrequency analysisobserverreduced order observersimulink

I want to do a frequency analysis of a state observer. Observer has two inputs. Control input u and the output of the plant y. Output is the state vector. I'm not sure how to select the inputs and the outputs to draw the bode plot. Basically I want to demonstrfate that a reduced order observer has a low phase lag than a full order observer but I can't figure out how to select the inputs and outputs to draw the Bode plot.

Best Answer

Hi,

I'm sure that you can find an example similar to your problem in the Bode documentation:

https://mathworks.com/help/ident/ref/bode.html

Related Solutions

MATLAB: Bode() magnitude

Magnitude and phase outputs of bode are 3-D arrays, for representing multi-input multi-output systems. The first two dimensions correspond to the number of inputs and outputs, the third dimension corresponds to the number of frequency points. In your case you have a single-input single-output system, so size(mag) is 1 1 n, where n is the number of frequency points.

To get a standard bode plot you can just do

bode(sys)

If you want access to mag and phase as regular vectors, just do

mag=squeeze(mag)

All of this is covered in the doc.

Arkadiy

MATLAB: Bode Diagram

You need to use bodeoptions command and set PhaseWrapping to on. Here is an example showing how to do it:

>>s=tf('s'); %define Laplace variable

>>freq=logspace(-1,2,1000); %define frequency vector

>>sys=1/(s^3+2*s^2+3*s+1); %some tf with phase <-180

>>bode(sys,freq) %phase is not within -180:180

>>p=bodeoptions

>>p.PhaseWrapping='on'

>>bode(sys,freq,p) %phase is wrapped inside -180:180

HTH, Arkadiy

Best Answer

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