Hi PLECS,
When I do simulation in PLECS and try to evaluate the RMS current that the DC link capacitor may see. Do you know up to how many order harmonics will this RMS block counted for? I see in FFT analysis, it can analysis up to 500kHz.
Thanks!
Bowen
Hello Bowen,
The RMS and THD calculations do not use a harmonics-based approach.
For a variable-step solver with a continuous time implementation (Sample time of RMS/THD block is “0”) then the uppermost harmonic accuracy is mostly limited by the numeric accuracy of the solver and its tolerance settings.
If you are using a fixed-step solver or specify a non-zero sample time in the RMS/THD component’s mask, then any harmonics above f_sample/2 cannot be correctly calculated according to Nyquist’s theorem.
Regards,
Bryan
Hi Bryan,
Sound good, and do you know is there some way in PLECS to see the harmonics above 500kHz of a given signal?
Thanks,
Bowen
Where are you getting the 500 kHz value from? Perhaps from the PLECS simulation scope? Note that this is a different analysis. You can set the harmonic order by changing the Number of Fourier Coefficients field (N) in the scope window.
If that’s not what you’re referencing then can you clarify further?
Hi Bryan,
Yes, it’s from PLECS simulation scope, I set base frequency as 50Hz, and N as 10000times, so it results max 500kHz harmonics. When I try to change the N to a higher value, then the scope will not respond? Is the scope limited to 500kHz? Or there is some other way i can see higher harmonics in the system?
Thanks,
Bowen
In the Number of Fourier Coefficients (N) in the PLECS FFT scope is limited to 10000. If you need to see the harmonics at a higher frequency then you must increase the base frequency from 50 Hz.
Note that this setting only impacts the values shown in FFT scope window. The RMS/THD calculations in the PLECS simulation model and in the PLECS Scope’s data window do not use the data displayed in the FFT scope window.
Sound good, thank you Bryan.
