A photovoltaic power system includes a DC/AC inverter circuit, N DC/DC converter circuits that are located at a previous stage of the DC/AC inverter circuit and that are respectively connected to photovoltaic strings, and a controller connected to the DC/AC inverter circuit and the N DC/DC converter circuits. The controller is configured to: perform MPPT control on n DC/DC converter circuits, and perform CPG control on (N−n) DC/DC converter circuits. In the two control manners, a fast and accurate power reserve or limit of a photovoltaic string inverter with any illumination intensity and ambient temperature can be implemented, and fluctuation of a DC bus voltage and AC output power of the photovoltaic string inverter can be eliminated. Control on a virtual synchronous generator of the photovoltaic string inverter is implemented, and a lifespan of the photovoltaic string inverter is prolonged, without a need to add an energy storage element.