To address the issues of difficulty in accurate power reservation for standby photovoltaic inverters under resource fluctuations

and issues such as DC transient overvoltage/undervoltage caused by power imbalance between AC and DC sides under dual disturbances of irradiation/grid fluctuations

this study constructs and analyzes the behavioral model of photovoltaic arrays. A method for estimating the maximum power of photovoltaics in the absence of additional irradiation or temperature sensors is proposed. Based on the difference in time scales of environmental irradiance and temperature variations in photovoltaic power generation scenarios

a dual-loop and dual-update cycle online correction method for the power reserve coefficient of grid-forming inverters is introduced. Additionally

a DC voltage stabilization switching strategy under extreme conditions is developed. Consequently

accurate online active power reservation for photovoltaic inverters can be ensured under varying irradiance and temperature conditions

enabling storage-free photovoltaic systems to provide active power support and maintain DC voltage stability under both resource fluctuations and grid frequency disturbances. The effectiveness of the proposed method is verified by experiments based on RT-LAB hardware-in-the-loop experimental platform.