Electronics > Power/Renewable Energy/EV's

Help with designing a 600V input Dcdc converter

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NiHaoMike:
How about a half bridge design? Then the primary voltage as seen by the transformer would be halved. Also consider using an off the shelf switching power supply module designed to run from 400V AC, rectified that would be about 566V DC.

trtr6842:
One characteristic of Vicors SAC's are that they are fixed ratio.  You cannot achieve a variable output with just a SAC alone.  All of the regulated output VICOR modules that use a SAC also include a non-isolated ZVS buck-boost to provide regulation, but with some extra losses.

No matter what topology you choose, odds are you're going to need to design custom magnetics.  DIY'ing your transformer and inductors can be cheap and give you very good efficiency.  Here you can find a magnetics design guide I wrote, an AC winding loss spreadsheet I wrote, as well as some other magnetic core analysis tools that might help.  DigiKey and Mouser usually carry ferrites, and you should be able to find something suitable there.  If you want powder cores and are in the US, CWS Bytemark has cores available with a reasonable minimum order quantity.  At thsi power level you probably won't need LITZ wire, and standard magnet wire is easy to source, and you won't need much for a 200W converter.  I am happy to help with detailed magnetics design.

One question for your specs, do you want a constant 200W output power over the entire 12V to 48V output range?  This would be called a wide range output power supply.  Or would just 12-48V, 0-4.2A be ok?  That is a much more standard spec.  There's a big difference between those two, and it will affect your design choices.  If you want the wide-range option, you'll probably be pushed towards a powder core output inductor for the soft saturation, and it would likely rule out a single stage LLC.  If you're ok with the 4.2A limit, then a ferrite output inductor will be more efficient and smaller, and you might have some more topology options.

Also, you mentioned 588VDC as your nominal input voltage, but what is the whole voltage range you need to operate at / survive?  That can change things a lot.  Also, do you have any EMI/EMC requirements?  Or is this jut a one-off?

I think if you're ok with it not being super power dense, a 2-switch forward is probably the simplest way to go.  Super simple control, plenty of gate drive options, plenty of current sense options, and easy output voltage regulation.  You can get that up to 90% full load efficiency with SiC primary side MOSFETs and decent magnetics.  You might not even need synchronous rectification, depending if your input voltage range will let you use 200V schottky diodes for the output. 

You could always do a good old-fashioned hard-switched half bridge converter, nothing wrong with that.  Skip all the funky resonant design and control challenges.  It'll be fixed frequency, simple control, and adaptable to your wide output voltage range.  It'll help keep the transformer small and efficient, and you could do either a current doubler output or a center tapped output, both are easy to convert to synchronous rectification.  With SiC MOSFETs on the primary, 90%+ efficiency should be attainable.

If you do want to get fancy, and especially if you want a really wide range output, an LLC would be the way to go, maybe with an additional buck output stage.  The buck output stage would greatly simplify the LLC design, since it could have a fixed output voltage.  In that case LLC design and control is pretty straightforward, and there are so many all-in-one control IC's that can handle that no problem.  Then the output buck converter is pretty straightforward, you could probably use off-the-shelf power inductors.

For 200W any full-bridge topology will probably be overkill, but a PSFB with an extra beefy transformer would probably be able to tackle the whole wide range output in one stage.

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