tcleghorn
Member
- Location
- Little Rock, Arkansas
- Occupation
- Electrical Engineer
I've been looking at a few different brands of DC-block battery energy storage systems (BESS) and associated inverters.
The inverters are transformer-less types. Some inverter manufacturers say they always require an isolation transformer, other manufacturers say it is optional but sometime required by BESS manufacturers, and some AC-block BESS manufacturers don't require an isolation transformer at all.
The DC-side is always ungrounded or isolated in all cases. The AC-side can differ between grounded or ungrounded.
One manufacturer told me it had to do with common-mode voltage coupling to the DC-side from the inverter when the AC-side is grounded causing insulation overvoltage and that's why they require it. But, if the DC-side is ungrounded, I'm having a tough time seeing how the grounding of the AC-side would significantly affect it other than changing the capacitive coupling from the DC-side to the AC-side which should be very small to start with.
The issue reminds of when VFDs used to require isolation transformers to block common-mode currents.
The inverters are transformer-less types. Some inverter manufacturers say they always require an isolation transformer, other manufacturers say it is optional but sometime required by BESS manufacturers, and some AC-block BESS manufacturers don't require an isolation transformer at all.
The DC-side is always ungrounded or isolated in all cases. The AC-side can differ between grounded or ungrounded.
One manufacturer told me it had to do with common-mode voltage coupling to the DC-side from the inverter when the AC-side is grounded causing insulation overvoltage and that's why they require it. But, if the DC-side is ungrounded, I'm having a tough time seeing how the grounding of the AC-side would significantly affect it other than changing the capacitive coupling from the DC-side to the AC-side which should be very small to start with.
The issue reminds of when VFDs used to require isolation transformers to block common-mode currents.