Urgent Help: City of CT Cutting Off Axperts

This talk of interlocking relays seems to be misunderstanding the way I believe the Axpert's AC to DC charger to work. 

It's still possible that the Axpert uses the "TI trick" that I mentioned a year or so ago. If that is the case, then I believe it really is physically impossible for energy to be transferred from the battery to the AC input terminals, and the theoretical possibility of accidental back feeding doesn't apply. But for reasons I can't recall right now, I feel that this trick is less likely used than the below. 

When AC charging, the AC input terminals are connected to the full bridge (4 switching devices in a full H configuration). The only question is whether the way the inverter is configured is inherently an AC to DC converter (battery charger) or a fundamentally bidirectional AC to and from DC converter (inverter/charger) that is operated in the AC to DC direction, but is physically possible to be operated in the DC to AC direction. Any inverter that is synchronised to the AC supply with an inductor between the inverter's "output" terminals and the AC supply is capable of bidirectional power flow. Essentially, it is the phase difference between the two AC quantities (the inverter and the supply) that determines the direction and magnitude of the power flow. It's a simple vector difference ; the difference between two vectors of similar magnitude and a small phase difference is at nearly 90° from these two vectors. Since the current through an inductor is at 90° to its voltage, that means that the inductor's current and hence the current to/from the load/supply is either in-phase or 180° out of phase with the utility voltage. You need to be careful with your conventions here, but it's clear that the power flow can be into or out of the utility connection depending on the phase difference.

After all that, whether the AC charger actually charges the battery or exports from the battery (including power from PV panels) depends on the sign of some variable buried deep in the firmware of the inverter / charger. It literally could come down to a single bit. 

Having said that, the firmware is obviously designed to keep the power flow from AC to DC. The firmware is continually adjusting the magnitude of the power flow to reach a target charge current while not overcharging the battery. If power was being exported for any reason, and there is no such reason suggested, but hypothetically, then the battery current would be the wrong sign, less than the target current, the battery would not be overcharged (in fact being discharged) so the firmware would adjust the phase angle in such a way that power flow would move towards the AC to DC direction. Its entire purpose is to charge the battery, so everything it does will be to cause power to flow out of the utility towards the battery. So the possibility of back feeding is purely theoretical. 

However, whenever the inverter hardware is the same hardware as the charger, you can't prove the impossibility of back feeding with relay interlocks.