The AC model in the datasheet is obviously not plausible, as it suggests a bandwidth higher than the converter's switching frequency.
Thanks do you mean the AC model on page 29 (figure 24) of the PRM datasheet?.....
PRM datasheet:-
http://cdn.vicorpower.com/documents/datasheets/PRM48JH480T250A00-ds.pdf
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But the VTM parts are described as constant duty cycle, so they should be expected to have at least a conjugate pole response
Thanks, but the VTM48' module can be simply considered in the feedback loop calculation as a simple ideal transformer with NP/NS = 24/1
..We dont need to consider any poles or zeros in relation to the VTM module and the feedback loop calculation. That is, the feedback loop calculation of the schematic which is like the bottom diagram on page 2 of the PRM48' datasheet...i appreciate the poles and zeros of the VTM48' module are there...but we neednt consider them as the below extols....
Page 12 of the VTM48’ datasheet explains that partly because the VTM48’ is switched at such high frequency, we can ignore the poles and zeros associated with it, as they will be well beyond our crossover frequency..
The VTM48’ module can be treated simply in the feedback loop as an (almost) ideal transformer…
As page 14 of the VTM48’ datasheet says…
The SAC topology bases its performance on efficient transfer
of energy through a transformer without the need of closed
loop control. For this reason, the transfer characteristic can be
approximated by an ideal transformer with some resistive drop
and positive temperature coefficient.
…so we can see that the VTM48’ is very easy to handle from the feedback loop point of view…just an “ideal transformer” (almost) in the power path..
The following from page 13 of the VTM48’ datasheet confirms that the VTM can just be considered as a simple transformer component…
The overall AC impedance varies from model to model. For most models it is dominated by DC ROUT value from DC to beyond 500 KHz.
…and the crossover frequency of the PRM/VTM converter is going to be well under 500khz, so the VTM48’ module can be thought of as simply an “ideal transformer” in the power path….meaning it is very simple to handle from the feedback loop calculation point of view.
..All we need to do is refer the capacitance and the load Resistance at the secondary of the VTM48 module to the primary of the VTM48’ module….As such, the VTM48’ module introduces no real complexity to us in the feedback loop calculation..
VTM48’ datasheet
http://cdn.vicorpower.com/documents/datasheets/VTM48E_020_080A00.pdf
PRM48' datasheet
http://cdn.vicorpower.com/documents/datasheets/PRM48JH480T250A00-ds.pdf