A direct current combiner box, used in a photovoltaic power generation system, wherein the direct current combiner box comprises a fault detection unit, a protection circuit, and a boost circuit, and an input end of the direct current combiner box is coupled to a photovoltaic array in the photovoltaic power generation system, wherein the fault detection unit is configured to detect an operating parameter of the direct current combiner box, wherein the operating parameter comprises at least one of a residual current at an output end of the direct current combiner box, first insulation impedance to ground of the direct current combiner box, and an input voltage transmitted by the photovoltaic array to the input end of the direct current combiner box; the protection circuit is configured to send a protection signal to the boost circuit when the operating parameter meets a specified condition, wherein the protection signal is used to enable the boost circuit to adjust a first voltage of the photovoltaic array at the input end of the direct current combiner box to a second voltage, the second voltage is a zero voltage or a non-zero voltage not higher than a safety voltage, and the specified condition comprises at least one of the following: the residual current is greater than a first threshold, the first insulation impedance to ground is less than a second threshold, and the input voltage is greater than a third threshold; and the boost circuit is configured to: after receiving the protection signal, adjust the first voltage of the photovoltaic array at the input end of the direct current combiner box to the second voltage; wherein the operating parameter comprises the residual current at the output end of the direct current combiner box; the fault detection unit comprises a residual current detection circuit; and the residual current detection circuit is configured to detect the residual current at the output end of the direct current combiner box. the fault detection unit is configured to detect an operating parameter of the direct current combiner box, wherein the operating parameter comprises at least one of a residual current at an output end of the direct current combiner box, first insulation impedance to ground of the direct current combiner box, and an input voltage transmitted by the photovoltaic array to the input end of the direct current combiner box; the protection circuit is configured to send a protection signal to the boost circuit when the operating parameter meets a specified condition, wherein the protection signal is used to enable the boost circuit to adjust a first voltage of the photovoltaic array at the input end of the direct current combiner box to a second voltage, the second voltage is a zero voltage or a non-zero voltage not higher than a safety voltage, and the specified condition comprises at least one of the following: the residual current is greater than a first threshold, the first insulation impedance to ground is less than a second threshold, and the input voltage is greater than a third threshold; and the boost circuit is configured to: after receiving the protection signal, adjust the first voltage of the photovoltaic array at the input end of the direct current combiner box to the second voltage; wherein the operating parameter comprises the residual current at the output end of the direct current combiner box; the fault detection unit comprises a residual current detection circuit; and the residual current detection circuit is configured to detect the residual current at the output end of the direct current combiner box.