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How to calculate total harmonic distortion for a given signal?

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How to calculate total harmonic distortion for a given signal?
I have used 'spectrum analyzer block' in Simulink and it gives me about 13 percent THD, whereas when I use thd() function in MATLAB script I get around 3.3492e-06 percent.
(Signal is output of a LCL filter which has been fed with output of a sine-PWM inverter.)

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Rahul Kumar
Rahul Kumar on 15 Nov 2020
click on powergui block then select FTT analysis after that you find your THD spectra for perticular signal.
Millo Dacha
Millo Dacha on 16 Nov 2020
Following is the signal:
thd() function gives me 3.3422e-06 % THD whereas SIMULINK's 'spectrum analyzer' block gives me about 13% THD.
I require a function to get THD in MATLAB code.

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Accepted Answer

Joel Van Sickel
Joel Van Sickel on 17 Nov 2020
Hello Millo,
when you used the function, did you only provide the signal data, or did you provide attitional parameters? It is likely you should specificy additonal parameters to get the THD that you want. Please look at the doc page carefully to see what else you can specify: Also, please take into account, that the spectrum analyzer is doing a lot of extra work behind the scenes. This matlab function does not return the value in percent, but in dbc, so you need to convert to percent.
However, I find that using fft, while a bit more work, is also more intuitive to understand what is going on. There are numerous examples of calculating THD in the file exchange. Here is one of them.
Regards,
Joel

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More Answers (1)

Rahul Kumar
Rahul Kumar on 15 Nov 2020
click on powergui block then select FTT analysis after that you find your THD spectra for perticular signal.

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