An input end of each DC-DC conversion circuit in the photovoltaic system is connected to a corresponding photovoltaic string. Output ends of a plurality of DC-DC conversion circuits are connected in parallel to an input end of a DC-AC conversion circuit. A controller performs a partial IV curve scan on each of the DC-DC conversion circuits, and in a scanning process, controls a total input power of the plurality of DC-DC conversion circuits to be consistent with that existing before the scan; and obtains a sum of the maximum input powers of all the DC-DC conversion circuits based on the maximum input power of each of the DC-DC conversion circuits, where a scanned voltage of the partial IV curve scan is less than an open-circuit voltage. The partial IV curve improves scanning efficiency and obtains a maximum input power in a power-limited state, facilitating subsequent power dispatch and control.