I keep seeing a block diagram on web pages, that I assume was published by Mitsubishi, that doesn't make any sense to me so here is my take on how the different parts are connected.
I make the following assumptions, that of course could be wrong.
1) Mitsubishi is using Synchronous AC motors.
2) The inverters do more than convert 300VDC from the batteries to AC but also convert AC on overrun, or from the generator, or from external power into DC to charge the batteries. I have colored AC and DC differently to distinguish them.
Here's what I think happens:-
In Serial Mode the Generator creates AC (red) that is converted to DC (blue) by the Front Inverter box to charge the Li-Ion batteries. The Inverters ( front and rear) then convert DC (blue) to AC ( red) to drive the Synchronous AC motors.
When parked and charging the External Power from the socket on the side is AC (red) and is converted to DC (blue) by the Rear Inverter box to charge the Li-Ion batteries.
In "EV" Mode the Front and Rear Inverter boxes convert DC ( blue) to AC (red) to drive the Front and Rear motors.
In Parallel Mode the ICE drives the front axle directly and power to accelerate is supplied by operating the Serial Mode simultaneously instead of using a gearbox as in a conventional ICE driven vehicle.
If anybody thinks I have got it wrong please let me know.