MATLAB: How to calculate total harmonic distortion for a given signal

digital signal processingMATLABpower_electronics_controlsimulink

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.)

Best Answer

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.
http://www.sengpielaudio.com/calculator-thd.htm
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.
https://www.mathworks.com/matlabcentral/fileexchange/77092-harmonic-spectrum-and-total-harmonic-distortion?s_tid=srchtitle
Regards,
Joel
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