+/-260mT in 100kHz LLC transformer

[cupoftea]

Hi,
We took apart a 3kW EV battery charger.
Half bridge LLC transformer was PQ3535 with AL = 1600, 3C90 ferrite.
LP=640uH
np/ns = 1:2
Fsw = 100khz
Vin=400vdc
Vout = 250-420VDC.......PFC output volts could be varied up to 445VDC (AC input was 85-265VAC).
Switching frequency was always 100kHz, apart from some times when it was 200kHz...(but when 200khz, the LLC gate drives were each on only 25% duty, instead of the usual ~49%)

PQ3535 was gap padded to metal case top, which in turn gets screwed to heatsink, which i believe is water cooled.
Also, vertical metal heatsinks are gap padded to the PQ3535 sides.

Do you believe this +/-260mT could be gotten away with due to all the cooling used?

 

[biswaIITH]

Hi,
We took apart a 3kW EV battery charger.
Half bridge LLC transformer was PQ3535 with AL = 1600, 3C90 ferrite.
LP=640uH
np/ns = 1:2
Fsw = 100khz
Vin=400vdc
Vout = 250-420VDC.......PFC output volts could be varied up to 445VDC (AC input was 85-265VAC).
Switching frequency was always 100kHz, apart from some times when it was 200kHz...(but when 200khz, the LLC gate drives were each on only 25% duty, instead of the usual ~49%)

PQ3535 was gap padded to metal case top, which in turn gets screwed to heatsink, which i believe is water cooled.
Also, vertical metal heatsinks are gap padded to the PQ3535 sides.

Do you believe this +/-260mT could be gotten away with due to all the cooling used?

Oh yes. More than the core losses in LLC HB Transformer, I have seen copper losses being the dominant one. For your power lever & switching frequency PQ35/35 seems to be a borderline core. I hope you must have given proper attention to the over load condition or short circuit condition. It is must to have a proper cooling in your application. In many of the battery charger I have tested & designed, LLC transformer fails mostly due to in adequate cooling .

I suggest you do a complete potting of the Transformer in an aluminum box & then screw the entire the box on to the heatsink. It provides cooling to both core & winding.