The Victron Multiplus-II 48/3000 and 48/5000 are back on the CEC list, which allows them to be connected to the grid in Australia under grid code “Australia A”.
The category that these inverters have been approved for (AS/NZS 4777.2 APPENDIX M) means that they cannot export any of their own generated power to the grid, due to their inability to comply with a 60° phase shift.
With a normal ESS setup, a Fronius grid tied inverter could be used on the output side of the inverter, supplying the critical loads and feeding any excess into the grid.
When the grid goes down the Fronius is controlled by AC frequency throttling. When the grid is present, the Mult can’t throttle by frequency (as it is synced to the grid), so if the user does not want to export any AC coupled power to the grid it would use Modbus TCP to control the Fronius.
With the Australian grid code, this doesn’t seem to work. When the Multi sees any AC power being exported out of the input terminal, it disconnect from the grid and ramps the AC frequency up so that the Fronius shuts down. Once the Fronius has shut down, the Multi reconnects to the grid and stays connected until the Fronius starts up again and the whole pattern repeats again.
What should happen is that the Cerbo should be controlling the Fronius over modbus to prevent any export, but it just doesn’t seem to do it. I have even experimented with connecting a Fronius on the grid side of the Multi but telling the Cerbo it is on the output side, to see if it just can’t react in time, but it doesn’t throttle it at all.
Using Nodered, it is easy to throttle the Fronius over modbus based on the the SOC of the batteries and a few other factors, so there isn’t any issues with that particular mechanism. I have also seen a colour control device to ramp down an entire building of Fronius Inverters over the LAN, so it obviously will do this natively under some circumstances.
Selectronic inverters are also on the CEC list under Appendix M, meaning they can’t export either. This is also because they can’t meet the 60° phase shift requirements due to the transform based topology. They can, however, export AC coupled solar to the grid just fine. (the AC coupled inverter meets all of the AS4777 requirements) I believe this may be to do with the fact that Selectronic control the Fronius inverter via RS485 all of the time, and do not use frequency shift.
Can anybody shed any light on this?