How to get best spectral plot

Hi, I want to get a plot from the frequency domain from the stator current in a induction motor model. The current is illustrated in figure

I want it in the same "format" as this

but I can't seem to get close, this is my best attempt using pwelch

does anyone have a comment on how to proceed? Thanks in advance.

Answer 1

[Birdman]

How did you set your pwelch's options? If you set them correctly, then you should obtain a very accurate plot. For instance:

h1=spectrum.welch;
set(h1,'Windowname','Hann');
Fs=1000;
set(h1,'OverlapPercent',66.7);
set(h1,'SegmentLength',512);

The lines above make the necessary settings for your pwelch function.

myPsd=psd(h1,X(:,1)-mean(X(:,1)),'Fs',Fs)
semilogx(myPsd.Frequencies,myPsd.Data);grid on

Imagine that your data is X, if you run the two lines above, then you should obtain the same result in a better way.

Please enter OverlapPercent and SegmentLength carefully, according to your data. Hope this helps.

[Andreas Askvik]

Thank you for the answer. My data is a 20001x1 double array which is logged in a period of 2 seconds. I'm gonna to some reading about pwelch.

[Birdman]

Ok then, sampling is equal to 0.5Hz. place your data to the code and see what is going to happen. If the answer is useful, please accept it.

[Andreas Askvik]

Got some wierd graphs, but thanks for the help.

[Birdman]

What kind of graphs?

[Andreas Askvik]

I get this plot

[Birdman]

Use this:

myPsd=psd(h1,X(:,1)-mean(X(:,1)),'Fs',Fs)
semilogx(myPsd.Frequencies,myPsd.Data);grid on
set(gca,'XLim',[0.01 100])