Reference: https://www.victronenergy.com/live/assistants:pv-inverter-support
I have an AC coupled system that is not grid connected and thus I use the PV Inverter Support Assistant to throttle the PV Inverter when the battery is charged.
I get situations where the battery is full and I switch on a large load (like a bore pump) which will ramp the PV Inverter back up to full power. Once that load switches off, I sometimes have the batteries go into over-voltage protection which shuts down the system. The problem is that the frequency ramping is slow and the full output of the PV (3.5kW) will go into the batteries when they are already at a high voltage/SOC. As these are LiFePO4 batteries, this occurs at the steep upper section of the charge curve and raises the voltage too high before the frequency control throttles it back. Obviously, this will shut down the system with an unplanned outage.
I was reading the PV Inverter Support Assistant doco at the reference and notice the following:
To prevent DC and AC voltage overshoots because of varying solar irradiance and/or load fluctuations, it will limit the charge current already before battery voltage has rised up to the absorption voltage. It will derate the maximum charge current from 100% at 13.5 / 27 / 54V to 10% at 14.4 / 28.8 / 57.6V. These thresholds are not related to the configured absorption voltage.
This appears to cover 12V/24V/48V system voltages, however, does not cover the 48V-15S configuration such as I have with Pylontech batteries. The absorption voltage for these 52.4 and are already heavily saturated at the 54V defined above.
@Victron, Is it possible to update the assistant so that it can be configured to better support 15S batteries - such as adding a configuration option for this case?
I see a couple of workarounds that I could try:
1. Disconnect the CAN bus and manually configure charge voltages such that there is a bit more headroom at the top end - but I will loose a bit of battery capacity and invalid the Pylontech warranty.
2. My system uses a lot of automation, so I could install a contactor to disconnect AC from the PV inverter when SOC is 100%
I will probably have to use option 2 unless there are other options that I have not considered?
Any thoughts and/or suggestions?
Thanks,
Ron
