Hello,
I am in the process of modeling a back to back converter system, and am having some trouble pinning down the exact relation between the DC-Link Voltage and the resultant DQ-frame AC terminal voltage for a VSI using SVPWM.
I can't seem to find a consistent answer in the literature, especially when using D and Q axis modulation indices.
The best I could find was setting Vll = 2/sqrt(3) * m * Vdc, with m limited to sqrt(3)/2 resulting in Vllmax = Vdc. If this is correct, I am not 100% sure how to convert this to the DQ frame.
Thanks,
Max
Hello,
The relation you found is clear and correct, but if i got it right your problem is how to project this in the d-q frame. It is very simple as you are dealing with constants (the max value) so the answer is to multiply your voltage with the Concordia inverse transformation constant (2/phases number)-1/2.
Good luck.
Thank you - I will apply this transformation and continue investigation.
Hello,
read the attached paper for a complete model of the back-to-back converter.
Best regards
Mohamed
Your relation may not be correct, instead you can use: V_t(peak)=m_(peak)*Vdc/2, with V_t(peak)=sqrt(V_td^2 + V_tq^2), where V_t(peak) is the peak line to neutral ac-side voltage, V_td is the d-component of the ac-side voltage and V_tq is the q- component of the ac-side voltage. If the conventional PWM is employed, m can assume a value up to unity, whereas with the PWM with third-harmonic injection, m can be as large as 1.15. Note that V_t=Vll/sqrt(3).