POWER CONVERSION DEVICE

A power conversion device configured to be interconnected with an electric power system through a transformer, and configured to have unit converters cascade-connected, wherein reactors will become unnecessary, and the volume and weight thereof will be reduced. The power conversion device (101), interconnected with a three-phase power system through the transformer (105), and transmitting and receiving active or reactive power with the three-phase power system (100), has the secondary winding of the transformer (105) made to be open winding having six terminals (106 to 111); has a first converter group (112), consisting of a circuit that have three converter arms (113 to 115) which are star-connected, connected to three terminals (106 to 108) of the secondary winding; and has a second converter group (116), consisting of a circuit that have three different converter arms (117 to 119) which are star-connected, connected to three terminals (109 to 111) of the secondary winding; and also has the neutral point (the point where the star connection is made) (121) of the first converter group (112), and the neutral point (122) of the second converter group (116) made to be the output terminals of the power conversion device.