Why not a pair of IGBTs? Should be just workable at that frequency, or fine a bit lower. If you're going for lower switching losses in a compact package (hence the higher frequency) I guess that wouldn't work out; instead I would recommend SiC MOSFETs.
Paralleling MOSFETs is generally fine, but don't forget to consider stray inductance. In the Sam Ben-Yaakov video, he considers the current divider circuit formed by Rds(on)s. Add stray inductances in series with these, and change the current to a step or ramp source, and you will have a representation of current sharing in the switching circuit. Current equalizes after a few L/R time constants, so besides reducing stray inductance, it can actually help to have some additional resistance.
Note that the stray inductance is, always, the loop inductance, from one switch to its opposing switch. For the two-switch forward, that's one transistor, and its catch diode, through the local bypass capacitor. The other transistor and diode act in an independent loop, and that loop needs to have the correct inductance as well. (The bypass can be shared, that's fine -- as long as both inductances work out.)
A typical layout, with transistors lined up on a heatsink, you would need to alternate transistor and diode, and put bypass caps in front of the row.
It's not much more trouble to simply use fully independent inverters. Use a single transistor and diode per leg, and a pair of legs, with a transformer and all the support components (input bypass cap, driver, output rectifier..) per channel or phase. Use N phases, with a phase shift between each, to reach the desired total capacity.
This is a bit annoying to do at 1500W, so I don't know that I would bother to do it (probably, I would choose a single phase, or two phase interleaved, full wave, forward converter). It is the only practical way to scale up arbitrarily.
The fundamental problem with scaling, is what ultimately underlies this argument. It becomes much more apparent at low voltages: where stray inductances hit so much harder. Say you're doing a 12V to 1.0V Vcore supply on a motherboard. You need 100A out, so you're switching pulses of about 100A / N at the input, for N phases. A hundred amperes in a single stage is just preposterous: that's a 0.12 ohm switching load impedance to begin with, and even doing it at 100kHz, you have to contend with the reactance of even a very compact loop of 5nH being 3mohm, i.e., drawing a reactive power of 2.6% of the total power, give or take. And that's just at Fsw; basically all the harmonics are going into it as well. That reactive power is just going to be burned as switching loss, unless you go to lengths to conserve it (quasi-resonant snubber?), and even then, you can't snub very much of it because the snubber itself is going to have about as much stray inductance!
So you need to divide and conquer, and 10A per phase is far more manageable, indeed well enough that Fsw can be pushing 1MHz while switching losses stay quite comfortable.
Finally, the other side is this: why not just build a bunch of inverters and run them in parallel? Why phase interleave? The best part is, when phases are interleaved, their ripple currents interfere and partially cancel out. You can save on total capacitance and filtering this way.
Tim
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