Embodiments relate to the field of photoelectric technologies, and provide a method for controlling photovoltaic power generation, a control device, and a photovoltaic power generation system. The method is applied to the photovoltaic power generation system. The system includes at least one photovoltaic string and a control device, the photovoltaic string includes at least one photovoltaic module, each photovoltaic module includes a photovoltaic unit and an optimizer that is connected to the photovoltaic unit, and the photovoltaic unit includes at least one photovoltaic component. The method includes: periodically sending, by the control device, an output voltage reference value update instruction to an optimizer in each photovoltaic string; and receiving, by the optimizer in each photovoltaic string, the output voltage reference value update instruction, and updating an output voltage reference value according to the output voltage reference value update instruction.