Inverter eating up my power!

There may be several things involved.  I am not directly famiiar with parallel ganged 6648 operation so these comments are general technical aspects that can happen.

With their comm interconnect and syncronization process they likely have a scheme to conserve inverter overhead idle power if the load requirement can be met with one inverter.  Each inverter requires 30-40 watts just to idle so why waste the power if output AC load is met easily by one inverter.  The situation might be a different strategy if the inverters must be ready to take a high starting surge device where all inverters need to immediately available when the surge requirement might happen.  It does take a few millisecs to bring an idling inverter out of idle to active mode.  I am not sure how the 6648 handles this.

Second is charger setup for battery charging.  If one inverter has a float or absorb setting that is different from others each will try to regulate the battery to its respective setting.  The highest float or absorb inverter will try to push the battery to that level.  The lower setting inverter seeing higher then its setting will try to drag down the battery level. This can just push AC power back out to be sucked in by other inverter trying to keep higher battery voltage regulation setting.  Power just circulates around the two inverters in opposite directions.

I would expect with inter-inverter communications they should resolve this on its own but maybe for battery charge level it does not do this since it cannot be sure which of the two different settings is the true desired setting.  The best way to handle this would be the assigned master inverter is where user sets up parameters that are then communicated out to other inverter via comm bus.

A hybrid inverter is like a auto transmission with a particular 'gearing ratio' setting when it is running.  If battery is pulled higher in voltage by external source the AC hybrid inverter at a given 'gearing ratio' will force the higher voltage battery down by pulling DC current and pushing AC power output.  It may not change its 'gearing ratio' unless pushing to grid is disallowed or AC out loads are not sufficient to consume the AC current push from the inverter trying to drag down its battery voltage to meet the setting values.

So make sure all the inverters have the same battery charging parameters, and they match as there can be calibration accuracy variation on each inverter.  On my older series conected inverters I have to 'tweek' one of the battery float levels down 0.1v from other to minimize the circulating power issue because the calibration is not perfect between the two inverters.

Biggest user confusions on the XW inverters is there are so many setting parameters that can have inter-dependent ramifications to other settings that are not obvious to the user.

Just back down your max charging current settings on all the inverters to a very low level and see if your 2000 watt drops accordingly.

If you have a clip on DC amp meter you would also see the current flow direction and level into the various inverters.

You asked about the devices in the system another post. What have you got besides 4 xwp's? Network is critical on large systems.

Have you read the multiunit design guide from Schneider? What do they say?

A picture of the install may help to break this down. Everything good with firmware? There were fixes that applied recently for offgrid XWP's. I had 2 large ones that got fixed last winter.

This sounds to me like either config or firmware.

 So humor me to play along, what are you doing with this much power offgrid? A machine shop? Micro grid?

So Inv 1 is backfeeding via AC_out port to battery while 2-4 (assume that means 2,3, & 4) are forward feeding battery to their AC_out.  This is the circular power flow.

You did not mention about AC_in's on the various inverters so as per sheet shot I assume there is no AC_in to any of the inverters. 

The actual inverter circuit is hardwired to AC_out and all four inverters AC_Out  are hardwired in parallel and should be synchronized (unless you open an AC_out breaker on an inverter).

The fact you say inverter 1 is allowing backflow into AC_out port sounds like AC coupling in enabled.  I don't recall if AC_coupling function has to be user enabled or not.  Normally I would expect it to throw an error like AC_in connected to AC_out unless AC_coupling allowed. Perhaps the 6648 allows some backflow if there are multiple inverters tied in parallel but I would think it would only be for small period of time while inverters adjust there levels and would complain if 2kW is continously backfeeding unless AC coupling was allowed.

Assuming you have no actual defect in an inverter, you likely have a setup issue.   I would review manual for all the setups for running parallel inverters.  Also any AC_coupling settings.   If there is no AC_in, one of the four inverters have to be the master for phase synchronization.  If inverter 1 is running slightly off phase to other three it could show the issue you describe.

Does issue go away if you leave inverter 1 out of the mix? 

Does this issue remain the same if you have AC_in to inverters?  AC_in would be master for phase in this case.  If inverter 1 had a calibration problem between phase measurement and inverter phase setting it would immediately shut down when connect relay was closed to AC_in due to inverter overload caused by phasing not aligned well. Need to try this on grid and not a generator.

Also, check to make sure L1 & L2 wiring on AC_out's are not reversed on any inverter.

Yea RC, AC coupling is a default and should be left on for XW pro series.
 Still no answer on the firmware revision. I can't pry that out of you. Nice install and it looks to me like all of the basics were done. Can't see the external XFER, is it there?

This is what I used last winter but it sounds like you have had both ways of saving the internal 60A relays?

The screen below is for grid but the offgrid version is just swapping the connection over to AC2 and a genset.

If you are still with the problem, maybe you have damaged an internal relay? There are alot of contacts in the relays that have to be perfect.

 Pull the covers over the relay pcb and look for smoky plastic covers. If they are good, and it sounds like everything else is correct to me, then as RC said triple check your wiring. This issue is not normal with XWpro. The earlier issues with multiunit systems was fixed and both of my clients are good. Below is a screen of some of them. Has Schneider looked at your system from the cloud? You may want to insist on it or hire me😉

 I always try and follow the less is more for offgrid. Supporting huge loads is too much work and it can be cheaper in the long run to just spend the money on conservation of the loads. I know you do not want to hear that and it is impressive how much work you have put into this. Have a good day !

mike760 said:

Ok, I might have come across the answer while searching for something else.  It's an old doc but I think it clears things up to a certain extent.  Looks like this behavior of feeding power back through the output is by design.



Here's a link to the "Application Note":

https://download.schneider-electric.com/files?p_enDocType=Data+Bulletin&p_File_Name=AC+Coupling+Application+Note.pdf&p_Doc_Ref=976-0240-01-01

The paragraph after the yellowed paragraph is the crafty worded issue it can create.  Power has to go somewhere.  When backfeeding ACout, choices are push it to grid or push it to battery.  If grid is not present or setup blocks backfeeding grid then only thing left is dumping to batteries. 

What the text below yellowed paragraph says if battery is full 'the charge is terminated'.  What it doesn't say is with no alternative place to push the power the only choice is to shut the inverter down when battery cannot accept any more backflow power. 

The inverter could raise the ACout voltage until backflow drops to zero but that is not a viable option beyond a minor increase.  This is what the parallel inverters do to regulate the load leveling but again it should only be a slight change  in ACout voltage.

What the op's problem is the other three parallel inverters are sucking down the battery so inverter 1 can backfeed to battery.  Round and round the power flow goes. One of the inverters, likely #1, is incorrectly interpreting its ACout voltage or battery voltage.  Having different battery charge voltage settings between inverters, like inverter 1 thinks the battery voltage is lower then its float voltage setting,  is usually the cause of this if just a setup issue.  Internal unit calibration for voltage reading being off can also cause it.

Actually that brings up a point.  If battery cabling has more loss to one inverter it could cause something like this. Could be something as small as a poorly tighten or crimped lug connection.  That connection would likely get warm.

From what the text imples the backfeed limit is based solely on battery absorb voltage setting.  This may also mean, other then absorb voltage setting, all other charging parameters are ignored, including charging disabled setting.  This makes sense since there is no other option then having the battery take all the backfeed power. 

Wording is a little wrong "bulk voltage" should read "absorb voltage"