Abstract: A power conversion device used in a DC power transmission system having a multipolar configuration includes: a self-excited AC/DC converter configured to convert electric power between an AC system and a main line; and a controller. The controller is configured to: receive an input of a current value between a neutral point and a DC terminal of the AC/DC converter; control an operation of the AC/DC converter; and control a switch to be opened and closed, the switch being provided between the DC terminal and the neutral point. When the current value is equal to or greater than a predetermined threshold value, the controller stops a plurality of cells and subsequently closes a bypass switch. When the current value is equal to or greater than a predetermined threshold value, the controller opens the switch.

Abstract: A protection device for a power converter provided between an AC system and a DC power transmission system is configured to: receive an input of an AC current value obtained between a transformer connected to the AC system and the power converter capable of converting AC power into DC power; receive an input of a change rate of a direct current detected by a Rogowski coil provided between a DC line and the power converter, the DC line receiving DC power from the power converter; determine based on the AC current value and the change rate whether a fault occurs or not in one of the power converter and the DC line; and output information for protecting the power converter based on a determination result.

Abstract: A protection device for a power converter provided between an AC system and a DC power transmission system is configured to: receive an input of an AC current value obtained between a transformer connected to the AC system and the power converter capable of converting AC power into DC power; receive an input of a change rate of a direct current detected by a Rogowski coil provided between a DC line and the power converter, the DC line receiving DC power from the power converter; determine based on the AC current value and the change rate whether a fault occurs or not in one of the power converter and the DC line; and output information for protecting the power converter based on a determination result.

Abstract: A power conversion device used in a DC power transmission system having a multipolar configuration includes: a self-excited AC/DC converter configured to convert electric power between an AC system and a main line; and a controller. The controller is configured to: receive an input of a current value between a neutral point and a DC terminal of the AC/DC converter; control an operation of the AC/DC converter; and control a switch to be opened and closed, the switch being provided between the DC terminal and the neutral point. When the current value is equal to or greater than a predetermined threshold value, the controller stops a plurality of cells and subsequently closes a bypass switch. When the current value is equal to or greater than a predetermined threshold value, the controller opens the switch.