Power conversion device

A power conversion device comprising:

• a power converter including an arm configured with one unit converter or a plurality of unit converters connected in series;
• and
• a control device configured to control the power converter,
• the unit converter including
• a main circuit including a switching element and a direct-current capacitor and configured to output a voltage pulse according to voltage of the direct-current capacitor by turning on/off of the switching element,
• a control circuit configured to transmit a voltage detected value of the direct-current capacitor to the control device and to control on/off of the switching element in accordance with a control signal received from the control device, and
• a switch configured to turn on in response to an on command from the control circuit to short-circuit output terminals of the main circuit,
• the control device being configured to compare a plurality of the voltage detected values received from the unit converters with a first threshold voltage and, when at least one of the plurality of voltage detected values exceeds the first threshold voltage, transmit the control signal for fixing the switching element to an off state to the control circuit of each of the unit converters, and
• in each of the unit converters, the control circuit being configured to compare its own the voltage detected value with a second threshold voltage higher than the first threshold voltage and, when the voltage detected value exceeds the second threshold voltage, the control circuit autonomously being configured to fix the switching element in its own the main circuit to an off state and turns on the switch, irrespective of the control signal.