Estimating Models Using Frequency-Domain Data

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Mohammad Tauquir Iqbal 2020-2-14

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评论： Star Strider 2020-2-14

i have got frequency domain dta from the experiment in dB and phase. when i used ystem identifcation tool box it is not accurate .

can anyone suggest how to prceoeed.

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Star Strider 2020-2-14

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Do not use dB.

If you are starting with the idfrd function, note that the documentation states:

The 'ResponseData' property stores the frequency response data as a 3-D array of complex numbers.

Amplitudes in decibels are not complex numbers.

If you are using the iddata function, see the documentation section on Frequency-Domain Data . Note that for it ‘...the data, which consists of the complex-valued input-output frequency-domain data U and Y, frequency vector W, and sample time Ts.’

Again, amplitudes in decibels are not complex numbers.

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Mohammad Tauquir Iqbal 2020-2-14

is this code right ?

i tried with increased number of pole as well

Star Strider 2020-2-14

It appears to be correct. I cannot tell from here.

Note that plotting the imaginary part of the Fourier transform will also let you estimate the number of zeros. Those are (obviously) the zero-crossings of that plot.

It is possible to have a pole or zero at the origin, and a pole or zero at infinity as well. You need to examine that plot carefully to be certain to detect them, and then include them if they exist.

Pole-zero cancellations should not exist in an estimated system. You can use the minreal function on the estimated system to be certain that they do not.

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