MATLAB: Nyquist plot from frequency response data

frequency response dataMATLABnyquist plot

Hi all,

I have a complex vector containing the response of a particular system to frequencies, given in another vector. How do make a bode plot? If I use the nyquist() function, I get the following warning message.

The numerator or denominator of this transfer function has complex-valued coefficients.

Therefore, I'm really not sure if the plot is correct or not.

Thanks

Best Answer

See the documentation on Data Preparation (link) for the System Identification Toolbox.

Related Solutions

MATLAB: How to make sure that the Bode magnitude plot always always starts from 0 dB

The Bode magnitude plot starts from a non-zero offset because of the transfer function's DC gain. This can easily be obtained if s = 0 is substituted into your transfer function, which corresponds to a zero-frequency (hence static) input. The only way you can make the Bode magnitude plot start from 0 dB in this case is to factor out the DC gain from your transfer function.

The DC gain can easily be calculated using the "<https://www.mathworks.com/help/releases/R2016b/control/ref/dcgain.html dcgain>" function and then the transfer function can be divided by this constant number. Now the Bode magnitude plot will always start from 0 dB because the resulting transfer function has unity DC gain.

MATLAB: To plot Magnitude of a system versus angular frequency

The easiest way:

s = tf('s');
sys= 1/(s + 2);
figure(1)
bode(sys)

See the documentation on the bode (link) function for details. (If you want to change the plot properties, you cannot in the plot bode produces. You have to get the magnitude, phase, and frequency as outputs from bode. You can then use subplot to plot them as you want them.)

Best Answer

Related Solutions

MATLAB: How to make sure that the Bode magnitude plot always always starts from 0 dB

MATLAB: To plot Magnitude of a system versus angular frequency

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