QUESTION
Is it possible to automate Quattros rejecting AV In due to high voltage disconnect without leaving Fronius PV generating 0W (it can be done manually by changing mode from “On” to “Inverter Only”)?
BACKGROUND
We have a large, 3 phase 135kva system (9 x 15kVA Quattro). The system is configured as an ESS (without excess feed in) and is connected to an unstable, 3rd world grid which experiences regular power failures and fluctuating incoming voltages.
Solar generation is 80% via Fronius PV (on AC Out) and 20% MPPT.
On occasion, mains power comes on during the day. It is always good outside of peak solar generation hours to subsidise battery charging with this. Sometimes incoming voltage is in an acceptable range. At other times though, the voltage goes into the 260-265V range. In these cases, for protection purposes, the Quattros are configured to reject the incoming power. The knock-on effect is that the Fronius PV inverters drop their solar output to zero. Without manual intervention, we start dipping into the batteries very quickly - even when there is ample sunlight available.
I have set up alarm rules to notify us when input voltages on any of the phases cause a high voltage disconnect. The notifications allow us to manually change the Quattro mode from “On” to “Inverter Only”, the Fronius inverters then start generating again as expected. The Quattros continue to monitor the incoming AV voltage - and we get RECOVERY notifications once phase voltages are good again. This allows us to revert to “On” mode.
Given the above manual process, I had hoped that in rejecting the incoming AC, the inverters would disconnect that power source (essentially going into “Inverter Only” mode for all intents and purposes) and thus allow the 3 x Fronius to come back online. At the moment, it seems to be caught in the middle, disconnecting on high voltage but still trying to sync frequencies with the Fronius.
NOTES
- We have engaged the power utility to adjust the voltages at the local sub station/transformer, but this has not happened yet. Realistically, it cannot be relied upon as a long term solution.
- In an ideal world, a 3P voltage stabiliser would make the above an non issue. However, funds do not allow for such an investment at this stage.
