MATLAB: How to remove delay from idtf object

idtfSystem Identification Toolbox

I'd like to use the inv() function for an idtf object to generate a predistorted waveform. Right now I cannot because the inverse is noncausal due to a 13 second iodelay in the original transfer function. How can I remove the iodelay from the idtf object?

Best Answer

You will need an invertible realization. Try high order transfer function estimations with no delays. Or, if the estimated model with delays is a good/accurate model, compute its frequency response (freqresp), invert it, and fit a transfer function to the inverse frequency response.

For literally just removing the delay you can do model.ioDelay= 0

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MATLAB: How to get transfer function from a bode plot data

This example shows how to do what you want.

You will need to create idfrd or frd objct to use with tfest. In addition to gain, you also need phase data to create a complex number at each frequency to represent your system response.

To construct frd or idfrd object, you need the gain of the system, not in db. To convert from db:

gain=10^(gaindb/20);

Create idfrd object:

response = gain.*exp(1i*phase*pi/180);
Ts = 0.1; % your sampling time
w=whz*2*pi; %convert Hz to rad/sec 
gfr = idfrd(response,w,Ts);

Estimate 2nd ordertransfer function

sys=tfest(gfr,2);

Compute the gain in db:

[mag,ph]=bode(sys,w);
magdb=20*log10(mag);

MATLAB: Do i get a different pzmap if i use idtf or ss representation of the same system

I assume you are doing something like this:

G = idtf(num,den)
M=tf(num,den)
N=ss(G)

Now you expect G ,M and N to be identical and have same pzmap since they are basically the same system. However there may be small differences due to numerical computation accuracy issues if your system is of high order.

See the section "Recommended Working Representation" here:

https://in.mathworks.com/help/control/ug/conversion-between-model-types.html#f3-1039600

Best Answer

Related Solutions

MATLAB: How to get transfer function from a bode plot data

MATLAB: Do i get a different pzmap if i use idtf or ss representation of the same system

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