Buying 3 Multis and having them generate a 3 phase grid is possible but expensive and the idle consumption is very high. So the other route is having a single 5000VA Multiplus-II and generate a 3 phase failover grid from it.
Is there a phase converter that can be recommended that supports around 5000VA total power? Self consumption should also be low and it should be able to handle unbalanced loads between the phases. Its for a ESS system and the grid converter is just backup.
I found this device from Siemens: https://www.automation24.at/frequenzumrichter-siemens-sinamics-v20-6sl3210-5be25-5cv0
Here is the manual for it: https://media.automation24.com/manual/de/103596507_v20_operating_instructions_complete_de-DE_de-DE.pdf
Does not seem to complicated. Am I missing something?