fmeili1
Solar Enthusiast
I wonder what happens in detail just at the moment when a typical off-grid inverter AIO device like EG4-6500EX will be connected to the grid via AC-in (at the moment when the AC-in breakers are switched on - all at the exact same time - while the off-grid inverter is still running in inverter "Solar/Battery" mode)?
When the AIO was started without AC-in connected to the grid, the phase position of the off-grid inverter could not be related in any way to the phase position of the grid. At the moment when the grid will be connected to the AC-in there will be a phase shift between both inverter output and grid. It could be by coincident, that they are 180 degree phase shifted which could result in a maximum of 2*120V*SQRT(2)=340V volt difference per phase (and 680V when using L1 and L2) if one source would have it's maximum at +170V and the other it's minimum at -170V at that moment.
But, if the grid would not be used by the AIO at this moment (if it runs in "Solar/Battery" mode with SBU), this should not hurt.
BUT
The reason for my questions is the following:
To prepare grid-charging for the EG4-6500EX I connect the AC-in's of the AIO's to the grid only if required (some minutes before program 12 setting "back to grid" will be triggered). From time to time (not very often), it happens that some of the inverters show Fault F60 (backfeed protection) just at the moment when the grid get's connected to the AC-in's. Today I had such a situation (F60) again but this time additionally it forced all my GFI's in my house sub-panel to switch off (this was the first time the GFI's gets triggered).
Because of this behavior I wonder if the problem may have something to do with phase shift differences (pure coincident).
I don't know if and how an AIO with grid charging and bypass feature handles this situation.
Will the AIO try to synchronize it's off-grid inverter output to get in sync with the grid phase as soon as the grid will be to connected to the AC-in to be prepared when it must switch to bypass (to not run in a possible high voltage difference while switching to bypass)?
Because the problem occur at the moment when the AC-in get's connected to the grid and NOT at the moment when the inverter changes to bypass, something happens inside the AIO just at the moment when connecting it to the grid - but what could it be?
I know that the EG4-6500EX is based on Voltronic Axpert Max and these AIO's are basically able to feed energy back to the grid (as a typical grid tied inverter), but this feature is disabled in the firmware of EG4 and by most of the other clones (e.g. MPP Solar 6548). But there are clones which allows it (e.g. Phocos PSW-H-6.5KW-120/48V).
So in principle these inverter needs to be able to get in sync with a grid (at least when export is possible). I know that this is not really comparable because off-grid inverters are voltage-sources while grid-tied inverters are current-sources but maybe it's related?
I just try to understand how these devices will handle these situation at all.
Would a zero-crossing switch at the AC-in side help?
Theoretically a grid sense-input at the AIO which is connected to the grid would help the AIO's to sync it's off-grid inverter phase with the grid phase just to be prepared if the grid get's connected... would be nice...
When the AIO was started without AC-in connected to the grid, the phase position of the off-grid inverter could not be related in any way to the phase position of the grid. At the moment when the grid will be connected to the AC-in there will be a phase shift between both inverter output and grid. It could be by coincident, that they are 180 degree phase shifted which could result in a maximum of 2*120V*SQRT(2)=340V volt difference per phase (and 680V when using L1 and L2) if one source would have it's maximum at +170V and the other it's minimum at -170V at that moment.
But, if the grid would not be used by the AIO at this moment (if it runs in "Solar/Battery" mode with SBU), this should not hurt.
BUT
The reason for my questions is the following:
To prepare grid-charging for the EG4-6500EX I connect the AC-in's of the AIO's to the grid only if required (some minutes before program 12 setting "back to grid" will be triggered). From time to time (not very often), it happens that some of the inverters show Fault F60 (backfeed protection) just at the moment when the grid get's connected to the AC-in's. Today I had such a situation (F60) again but this time additionally it forced all my GFI's in my house sub-panel to switch off (this was the first time the GFI's gets triggered).
Because of this behavior I wonder if the problem may have something to do with phase shift differences (pure coincident).
I don't know if and how an AIO with grid charging and bypass feature handles this situation.
Will the AIO try to synchronize it's off-grid inverter output to get in sync with the grid phase as soon as the grid will be to connected to the AC-in to be prepared when it must switch to bypass (to not run in a possible high voltage difference while switching to bypass)?
Because the problem occur at the moment when the AC-in get's connected to the grid and NOT at the moment when the inverter changes to bypass, something happens inside the AIO just at the moment when connecting it to the grid - but what could it be?
I know that the EG4-6500EX is based on Voltronic Axpert Max and these AIO's are basically able to feed energy back to the grid (as a typical grid tied inverter), but this feature is disabled in the firmware of EG4 and by most of the other clones (e.g. MPP Solar 6548). But there are clones which allows it (e.g. Phocos PSW-H-6.5KW-120/48V).
So in principle these inverter needs to be able to get in sync with a grid (at least when export is possible). I know that this is not really comparable because off-grid inverters are voltage-sources while grid-tied inverters are current-sources but maybe it's related?
I just try to understand how these devices will handle these situation at all.
Would a zero-crossing switch at the AC-in side help?
Theoretically a grid sense-input at the AIO which is connected to the grid would help the AIO's to sync it's off-grid inverter phase with the grid phase just to be prepared if the grid get's connected... would be nice...