This application relates to a converter in a photovoltaic power generation system and a parametric curve scanning method for a photovoltaic string. A parametric curve includes a current-voltage curve or a power-voltage curve. The scanning method includes: controlling an output voltage of the photovoltaic string to change from a first endpoint voltage of a first voltage range to a second endpoint voltage of the first voltage range according to a first preset rule, to scan a first parametric curve; controlling the output voltage of the photovoltaic string to change from a third endpoint voltage of a second voltage range to a fourth endpoint voltage of the second voltage range according to a second preset rule, to scan a second parametric curve. There is an intersection set between the first voltage range and the second voltage range. In this application, whether a scanned curve is affected by a light change may be determined based on the first parametric curve and the second parametric curve. This is convenient and fast, and no additional hardware test device is required.