I have developed a grid-connected single-phase PV inverter consisting of DC boost converter and a full bridge inverter separated with DC link. I noticed that 0.98 power factor gives better real power output than at unity power factor.
I've read that in UPS power supplies unity power factor can also cause inverter derating and generally there seems to be a practice in the industry to avoid unity power factor due to overcompensation/resonance and is best to stick with 0.96-0.98.
I can only add that the inverter is transformerless, the LCL filter is not ideally designed for switching frequency than what is being used and I notice MPPT is more stable at 0.98. Overall inverter current output is higher at 0.98, but still can't put my finger on why?