Is there really a HVDC to battery voltage conversion step? I thought the whole point of quick charging is that you get exactly the DC that the battery needs right from the charger.
Actually, the superchargers take AC from the grid. The equipment at the supercharger consists of a rack of AC to DC converters run in parallel. That creates the DC that is delivered to the batteries at about 400 Volts.
As far as I understand, the car asks the Level 3 charger for a certain amount of volts and amperes, and the charger delivers exactly what the car needs (being able to vary the parameters for each type of car - and yes, those Level 3 DC chargers are big, complex, and expensive). Then the current goes directly to the battery. And this is why the charging gets so fast: there are no intermediate steps. The car just needs to provide cooling for the battery and control the charging process.
You're both right. A Level 3 charger does deliver the right DC voltage the car needs, and it does so using power electronics that convert regular old grid AC into DC.
Level 1 & Level 2 charging: AC grid -> cable -> onboard charger converts to 400V DC -> battery
Level 3 charging: AC grid -> offboard charger converts to 400V DC -> cable -> battery
Same number of steps, same conversion efficiency. Tesla even goes a step further and uses the same hardware, building out the (low volume) Superchargers "simply" by ganging together a dozen (high volume) on-board charger modules and stacking them inside a weatherized outdoor cabinet. This commonality maximizes their economies of scale.
Wouldn't there be an additional stepping at the transformer for level 1 and 2 chargers to go from AC distribution grid at 480V AC to 110V/220V where the level 3 superchargers can plug directly into the 480V AC mains without a transformer?
For anyone that's confused, it's because now we're really getting into the weeds of how the grid works. :) It's only fair to look back and compare from the same point in the grid, in order to be an apples to apples comparison. Really we should look at the whole electricity supply chain.
Level 1 & 2 charging: high voltage AC transmission line -> local substation converts to 480V AC -> distribution lines (poles or buried) -> pole-mounted or buried transformer converts to 110/220V AC -> household wiring -> cable -> onboard charger converts to 400V DC -> battery
Level 3 charging: high voltage AC transmission line -> on-site transformer converts to 480V AC -> offboard charger converts to 400V DC -> cable -> battery
