DC injection

DC injection is direct current that an inverter puts into the AC grid along with its normal AC output. Inverter datasheets usually list a DC current injection figure, for example below 0.5% of nominal output current on Sungrow central and string inverters. Many inverters include settable DC injection protection with a mode, a trip value and a trip time, and these can be turned on or off for each grid code. When the limit is exceeded the inverter logs a DC injection fault, which may be reported for each phase or as a total. Conformance testing checks the inverter against the IEEE 1547 limit, so check the DC injection settings during commissioning against the grid code that applies.

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• sentence 1: support check: partial - Passages give only the limit on DC current injected, not a definition of DC injection as direct current added to the AC output.
• sentence 2: support check: partial - Specific Sungrow figures below 0.5% are shown, but 'usually listed' across inverter datasheets and 'central and string' are not established.
• sentence 3: support check: partial - Mode/trip value/trip time and per-grid-code enable flags are shown, but 'many inverters' is not established and the per-grid-code columns just list default values, not independent toggling.
• sentence 4: support check: partial - Per-phase and total DC injection faults exist, but the passages do not say they are logged when the limit is exceeded.
• sentence 5: support check: partial - IEEE 1547 conformance test is stated, but the commissioning advice to check settings against the applicable grid code is not in the passages.
• sentence 1: review: partial - The IEEE 1547 passages only limit how much DC current a DER may inject; they never define DC injection as DC put into the grid alongside the normal AC output.
• sentence 4: review: partial - The Delta fault rows list DC injection faults per phase (R, S, T) and as a total, but none of them says the fault is logged when a limit is exceeded. -->