you can design the flyback circuit for reaching the critical
discontinuous mode at a lower voltage (e.g Vin(min)=200V;D.C=0.4); ypu will rich by calcul. a N1:N2~10, trafo ratio.
So, the reflected input voltage will be:10*12V=120V<<Vin=400V. No current feedback will occur during OFF periodes.500V...
try to find at EPCOS C.M choke.
The inductance is important, but you have to look at the characteristic L to frequency. Usually for EMC you need high induct. at 1-50MHz.
You need also a film capacitor after the bridge for the H.F switching current.
they use the average current mode regulation method, in which by placing the shunt inside the H.F AC power loop the loop compensation becomes much easier (some close to peak current mode)
actually by measuring the AC H.F current attached to DC output current a better pk-to-pk fast regulation can...
I think that:
1.you need a current sense for detecting fast a reverse current when battery is oppositely connected.
2.the shut-down of serie prot. mosfet to be activated by a current comparator, but also by a B-E`0.7V NPN transistor which will first limit the short current.
