I have been racking my brain over this one. I have this exact setup:
2x Quattros set up in split phase and the Autotransformer after the inverters to balance the 120v loads. When inverting, I am seeing nearly perfect balance between L1 and L2. On shore power it is all over the place. Is there a chance the neutral return is taking a different route via one of the ground wires and somehow bypassing the Autotransformer? Would that cause this? Any ideas where to look? I have used my clamp meter and do show some current flowing over the various ground wires in the RV. If I temporarily remove a ground it does not seem to help though. I am at a loss. I am connected to a shore power that only has a 30 amp limit across each phase and one Inverter always seems to start assisting before the other phase. It would be nice to use the Autotransformer as intended and get the most out of the shore connection we have.