Used Inverter?

If you like the TRW patent (1971, but likely the one you're thinking of), see how clearly you can recognize the basic idea (with the planetary connections rearranged a little and some other minor differences) in John Godfrey Parry Thomas's patent filed in 1908.

Then think about, if you were going to build the MG ECU using technology available in 1908 (or even 1971), what size room would you need?

To say nothing of the IPM. At least in 1971 there were transistors, but there weren't small IGBTs that could switch a hundred amps.

The simplest vacuum tubes were four years old in 1908.

An overview of the math the MG ECU is doing for you can be found in this post.