Conversion to AC motors

Yes, both the present DC Chopper traction system and the three phase AC systems will operate from the 3rd/4th rail system. Once they are all in service it's possible that some change to the traction supply protection settings might take place. There's no reason in principle why AC and DC units shouldn't run together. LU might, however decide for reasons other than the traction packages (eg other modified systems) to keep modified and in-modified units separate.

As noted, you should be easily able to run a DC motored train and an AC motored train together, the supply is remaining the same, and any/all of the enabling works to allow the operation of the AC motored trains (such as track circuit alteration) will not prevent DC motored trains from running. However, it is worth pointing out that even with all reasonable steps taken, the performance of a DC train and an AC train will not necessarily match - there were plenty of reports from SWT drivers about trains formed of an AC unit and a DC unit either pulling or pushing together whilst motoring and braking because they weren't quite identically performing - so it may well be the case that LU try to avoid running mixed trainsets for that reason.

Tangentially related, but how often do the Central line 2-car units get swapped around? It may well be the case that there aren't many opportunities for mixed trainsets to be formed. With my thinking cap on as well, I can imagine that LU would try to keep trainsets together to prevent situations where you've got a DC motored unit in the middle of a train that needs to be released for conversion - easy enough to rectify but better if avoided.

Thanks for the info.

As I understand it, the Jerky ride of the Jubilee and Northern lines is as a result of the train-based part of the ATO system only having "brake" and "accelerate" as options, and isn't related to the traction package. I wouldn't expect the retractioning to start messing around with the ATO system - it should just be replacing the traction system alone, everything upstream of that (ie the onboard computers, controls, etc) should all be remaining the same

Will these new inverters provide regenerative braking? I know it's easy with a DC controller but they weren't generally implemented. Then there's the issue of how high do you allow the rail voltage to rise, especially with DC stock still on the tracks.