I have an off-grid Victron system with two separate battery inverter systems connected through the same property AC network.
The Main System uses a Victron Quattro 48/15000/200 with a VRLA battery bank It has a Victron SmartSolar MPPT RS 450/200-Tr for DC solar charging 16kw solar . It also has two AC-coupled Fronius inverters, being a Fronius Primo 8.2-1 and a Fronius Primo 6.0-1, giving 14.2 kW of AC-coupled inverter capacity with 18.3 Kw of solar. The Main System uses a Cerbo GX and controls Fronius curtailment by frequency shifting.
The House System is connected downstream on the same property AC network. It uses a Victron MultiPlus-II 48/10000/140 with 3 x Discover HELIOS ESS 52-48-16000 lithium batteries in parallel, giving about 48 kWh, It also has a Cerbo GX and a Victron EV Charging Station connected downstream of the MultiPlus on AC output 1.
I am currently using Node-RED to coordinate the two systems. I now have a Raspberry Pi 5 running Node-RED above both Victron GX systems. It reads data from both systems and writes control commands where required I was running this on the Multiplus cerbo but was needing the odd reboot.
The aim is to have two separate battery systems supporting the same property AC bus. Ideally, I want power to move in either direction depending on operating conditions. During the day, I want the House System to charge from genuine excess solar from the Main System. When solar is low, I want the House System to change role and support the shared AC bus from its lithium batteries. I also want the EV charger to operate where possible without causing unstable power flow and using excess solar from the main system to charge - all of which I have working.
At the moment, I minimise frequency shifting by writing active power limits to the Fronius inverters through Node-RED using Modbus. This prevents the Fronius output from jumping too aggressively when the sun comes out from behind clouds. Without this, the Quattro can raise frequency quickly to curtail the Fronius inverters, which can upset the MultiPlus on the same AC bus. This Fronius Modbus limiting works reasonably consistently, although it is sometimes not fast enough and the AC frequency still rises above about 50.6 Hz, which starts tapering the Fronius output through frequency shift.
The MultiPlus is currently being managed by changing operating modes through Node-RED. During the day it can be placed in a charging mode so it draws from the main AC bus and charges the batteries. At other times it is placed into external control so it acts as a support battery and exports power back toward the AC input side of the MultiPlus.
The main problem occurs during generator operation. The generator is an AGG Power Solutions C33D5 with a DSE 7320 MKII controller. It is a 33 kVA three-phase generator, reconfigured for effectively single-phase use, with about 22 kVA usable output I run at about 84amps 230volt around 19kw. If there has not been enough solar to charge the Main System battery, the MultiPlus can disconnect from the AC bus when the generator starts. My current workaround is to put the MultiPlus into external control so it does not draw load from the AC bus until the generator has stabilised and is supplying power. Once the generator is stable, pass-through and EV charging can be allowed again if required.
I have not been able to reliably charge the Discover batteries from the generator through the MultiPlus. When I try to do this, I get swings in load, which can lead to disconnection. It appears that when the generator starts, the Quattro, which is not in ESS mode and is using frequency control, can send out around 53 Hz to disconnect or curtail the Fronius inverters. That high frequency also appears to cause the MultiPlus to disconnect from the AC bus.
I have looked at Victron microgrid firmware. The issue I see is that it does not appear to support AC-coupled PV inverters connected to the same bus in the way I currently rely on. That is a major concern because the Fronius AC solar is important. In summer, I have large HVAC loads across the same AC bus, including two 14 kW HVAC systems and one 10 kW HVAC system. At times, the property can have 14 to 15 kW of continuous load. The Fronius AC-coupled solar absorbs much of this daytime load, which reduces the load carried by the Victron inverters.
I do have the option to add separate DC solar for the MultiPlus system. That would allow the House System to charge from its own solar during the day, then change to external control after solar production falls and support the AC bus at night. However, this is less efficient than being able to distribute energy between the two systems according to battery state, solar production, generator state and property load.
The question is how best to configure and control this arrangement.
Has anyone successfully used Victron microgrid firmware in a system that still integrates AC-coupled Fronius solar on the AC bus?
If not, what is the best way to handle this - Quattro 48/15000/200 and a MultiPlus-II 48/10000/140 as two separate battery systems supporting the same AC bus, while also managing Fronius AC-coupled PV, generator operation, EV charging and bidirectional energy support between the two battery systems?
IS VICTRON GOING TO HAVE AC added to there microgrid?