Peak voltage on the DRSSTC caps?

[profdc9]

How do you determine the peak voltage on the capacitors for a DRSSTC?  For a SGTC, it's the voltage that the capacitors are charged to.  Because the capacitors in the DRSSTC are in a series resonant circuit, it is going to be the "Q" of the primary tank circuit times by peak supply voltage.  Is the Q roughly the reciprocal of the coupling coefficient between the primary and secondary coils, so for example, if k=0.1, and the peak voltage is 330 V, the peak voltage on the capacitor banks would be about 3300 V, so one, for example, should use perhaps double this voltage rating for the capacitors?

Thanks,

Dan

[Hydron]

You can work out the peak voltage on the capacitors by using the peak current (limited by OCD trip), frequency and capacitance.

If you know the frequency of the primary current (while running near OCD limit - it can change as streamer loading increases) then you can work out capacitor impedance from standard equations. With that and the OCD trip level (plus some margin for safety - the OCD will only trip after a full cycle so peak current can be a bit higher than the limit) you can work out the peak voltage seen across the capacitor.

All of this work is mainly for understanding though (which is valuable) - if you want to know the answer quick, Mads has made a calculator on his website!

See: http://kaizerpowerelectronics.dk/calculators/mmc-calculator/

[Mads Barnkob]

I always use the unloaded resonant frequency and the OCD setting, remember that we are talking ball-park figures anyway. It is all somewhere around +/- 3dB

MMC Xc, reactance: Xc = 1 / (2 * PI * F * C). F is frequency in Hertz. C is capacitance in Farad.

MMC Zc, impedance: Zc = SQRT(ESR^2 + Xc^2). ESR is the combined ESR for the MMC. Xc is the MMC reactanse from above.

Peak voltage MMC: DC peak voltage over MMC = Zc * primary peak current

You could also try Sigurthr's burst voltage calculator from here: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?160657.0#post_164912

Here's the link to download the .rar https://app.box.com/s/djhbgdrigduiu8628rz7

Just for reference; here are the formulae I used:
Ipk = V / (2Pi * Lpri * fres)
N = Vlimit / Vbus
(half bridge)
N = (Vlimit / Vbus) / 2
(full bridge)
Where:
N = number of switched half cycles. Vlimit = chosen peak tank voltage.