DC-DC converter from low voltage at high current, to high voltage at low current
160A at 25V will not give you 4kW out. If it is very well designed, you'll get around 3.2kW. The rest is wasted as heat. As you're just setting out to do this, and you're trying to design it yourself, you need to model it well and simulate to work out where your losses are going to be, and how you're going to cool it.

This is a perfectly do-able boost converter project. I have done a 5kW output DC-DC (admittedly that was 48V), and that required a full automotive style liquid cooling system. That was using a standard synchronous DC-boost converter, 48V came in, and we got up to 200V out.

First things are cooling and component ratings, those are the hard bit to do. 25V is low for 4kW, so you'll quickly see (once running the numbers) why it is that higher voltages are chosen for these kinds of power.

At 25V in, 4kW out, 80% efficient means around 200 Amps in, plus a 50% overhead safety factor for your FETs, so you need to find FETs rated to 300A, 800V (high voltage due to high output voltage requirement). Don't forget to de-rate for temperature, and check your simulations for junction temperature rise. I say your FETs, but it doesn't have to be FETs, I've used FETs and I've used IGBTs for this kind of work, some people say GAN transistors would also work (but I've never used them). Depends on the voltages, currents and switching frequencies you're looking at. But that in turns depends on your application, budget, size constraints, development time allowed etc.

You'll also need an inductor, rated at similarly. But these are probably easier to find.

You could split the power down, using multiple channels in parallel, each channel doing a part of the current (I used 3 channels on my 5kW system). But still, cooling will be your biggest challenge.

You can then build it, find out what fails, what mistakes you made in your simulations, and then repeat the process until it works how you want it to work.

In summary:


It will get hot
You need to simulate it
Don't underestimate how hot it will get
You can just scale up a standard DC boost converter
Watch your cooling
Simulation is vital