A power supply device for an HVDC controller, comprising: a first High Voltage Direct Current (HVDC) converter unit connected to an active power grid; a second HVDC converter unit connected to a passive power grid, the second HVDC converter unit being capable of receiving first DC power from the first HVDC converter unit by being connected to the first HVDC converter unit via a Direct Current transmission line; and an HVDC controller, arranged to control the second HVDC converter unit, for receiving a DC power from the passive power grid when the passive power grid is operating normally and for receiving the first DC power from the first HVDC converter unit when the passive power grid is not operating normally, wherein the HVDC controller includes a voltage distributor and a DC-DC converter, wherein the voltage distributor is configured to receive the first DC power and to output a second DC power which is acquired by dividing the first DC power and is lower than the first DC power, wherein the DC-DC converter is configured to receive the second DC power by being connected to the voltage distributor, to convert the second DC power into actuating power to be used by the HVDC controller, and to output the actuating power, wherein the second HVDC converter unit includes the HVDC controller having a power supply selection switch, and wherein the power supply selection switch is configured to selectively apply the actuating power, applied from the passive power grid when the passive power grid is operating normally, or the actuating power, applied from the DC-DC converter when the passive power grid is not operating normally, to the HVDC controller by being switched based on control by the HVDC controller. a first High Voltage Direct Current (HVDC) converter unit connected to an active power grid; a second HVDC converter unit connected to a passive power grid, the second HVDC converter unit being capable of receiving first DC power from the first HVDC converter unit by being connected to the first HVDC converter unit via a Direct Current transmission line; and an HVDC controller, arranged to control the second HVDC converter unit, for receiving a DC power from the passive power grid when the passive power grid is operating normally and for receiving the first DC power from the first HVDC converter unit when the passive power grid is not operating normally, wherein the HVDC controller includes a voltage distributor and a DC-DC converter, wherein the voltage distributor is configured to receive the first DC power and to output a second DC power which is acquired by dividing the first DC power and is lower than the first DC power, wherein the DC-DC converter is configured to receive the second DC power by being connected to the voltage distributor, to convert the second DC power into actuating power to be used by the HVDC controller, and to output the actuating power, wherein the second HVDC converter unit includes the HVDC controller having a power supply selection switch, and wherein the power supply selection switch is configured to selectively apply the actuating power, applied from the passive power grid when the passive power grid is operating normally, or the actuating power, applied from the DC-DC converter when the passive power grid is not operating normally, to the HVDC controller by being switched based on control by the HVDC controller.