Comment by londons_explore
2 days ago
> 400V electric vehicles and 400,000V transmission lines play by different rules.
When stacked, they don't. Plenty of research on stacking both MOSFETs and entire power converters.
With stacking, the figure of merit (ie. Kilowatts per dollar, loss percentage) isn't a function of voltage (although the fact that you have to have an integer number in series and parallel could influence the design if you want to use off the shelf components)
Today's HV converter stations use IGBT's mostly because they used to be the best thing to use back in the 2010's when the design process for them started.
The reasons for using IGBTs is not only because BJTs withstand higher voltages, but also because their Vce(sat) can provide much lower loss than Rds(on) at high currents. I x V vs I^2/R.
Vce never really goes below 2 volts... Which for a 1000 amps means the running costs of the converter are 2000 watts * number of stages (~2800). 5.6MW of heat. That quickly dwarfs the purchase cost of those IGBTs.
Whereas the same calculation for MOSFETs [1] gives 4242 stages and an Rdson of 1.9 milliohms... = 8 Megawatts! Which sounds worse... But you can parallel the MOSFETs by spending double the money on them, reducing the loss to 4 megawatts... Or you can double it again to reduce the loss to 2 megawatts, etc.
When you run something 24*7, energy losses cost way more than capital costs - and MOSFETs let you make that tradeoff, whereas IGBTs do not.
[1]: https://www.infineon.com/cms/en/product/power/mosfet/silicon...