H-Bridge as Battery Charger

[naseerak]

I have design this Hbridge circuit with the help of the forum members, now I want to use the same bridge circuit for battery charging with current sensing on the primary side of the transformer using C.T (current Transformer). I want to know which mosfets to keep pulsating and which to keep on, I dont want PFC feature which may complicate the coding and hardware.
my little knowledge says that I have to keep the upper (high side Mosfets) off and keep pwmming the lower mosfets, but is necessary for me to detect the zero crossing or not.
and what are the maximum and minimum duty cycles.

 

[ALERTLINKS]

Why parallel FETs have not similar gate drive?

 

[naseerak]

To reduce the parts count, saw also an imported FET power board from ebay with the same method. If you have some series reservations then I will reconsider my design.