When sun is first coming up, the panel illumination current is low. It does not take much illumination for panel to reach Voc dependent only on panel shunt leakage current. Because of low illumination current, the panel voltage will immediately collapse if a small amount of external load is attempted to be placed on panel. Detecting the open circuit panel voltage, the MPPT charge controller starts up but there is not yet enough illumination current to sustain the controller.
It attempts to determine an MPPT point but voltage just quickly collapses because there is not enough current to run the DC-DC converter reliably.
All-in-one HF inverters normally charges to the internal HV DC node, which for a 120 vac HF AIO inverter is typically about 250vdc.
The SCC controller in HF AIO inverters are normally just boost converters. This is why the PV input voltage is never allowed to exceed the internal HV DC supply node voltage.
It might go into a mode that sucks what it can from charged up PV input electrolytic caps, depletes the caps charge down to minimum voltage the boost converter can run on, then repeats the processor over and over again until the illumination current gets great enough to sustain the DC-DC boost converter.
If a poorly desiged AIO SCC boost does this process of sucking what it can from the PV input caps and does not stay off long enough for PV current to recharge the input capacitors to a high enough voltage, it might get locked up in the condition you describe.
You have to real careful about the AIO PV inputs not being isolated from inverter AC outputs with grounded neutral on AC output.
As I mentioned, most solid state DC relays are not bi-directional switch and will pass reverse current through the single MOSFET body diode. The reverse current I am concerned about is the non-isolated PV input voltage from AC output H-bridge. The PV lines ride on top of this non-isolated H-bridge switching voltage when inverter AC output is active. This is why double pole breakers, breaking both PV pos and neg lines is required.
If the PV SCC in your AIO is suffering the startup condition issue I described, and it does not eventually fix itself when illumination current gets great enough, the only way to break the startup oscillation issue would be break the panel connection until the sun generates enough panel illumination current to supply the SCC startup current demand without the input capacitors voltage collapsing to minimum run voltage of SCC boost converter. You might even need to provide more capacitor storage across panels to provide the initial SCC startup current. Are you going to do this every time a heavy cloud or a shading condition drops out the SCC?
Before going through an attempt at a bandaid fix you should at least try to get a replacement SCC board and see if that fixes issue.
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