Power conversion apparatus and power system

A power conversion device comprising:

• a power converter including a plurality of phase arms in which a first arm and a second arm for each of phases are connected in series to each other, the plurality of phase arms being connected in parallel between positive and negative DC lines, the power converter performing power conversion between three-phase AC and DC;
• and
• a control device which generates respective voltage command values for the first arm and the second arm and performs drive-control of the power converter on the basis of the voltage command values, wherein
• the first arm and the second arm each include a converter cell composed of:
• a first series body having semiconductor switching elements in both of upper and lower arms;
• and a DC capacitor connected in parallel to the first series body,
• the converter cell in the second arm is a second converter cell formed by connecting the DC capacitor, the first series body, and a second series body in parallel, the second series body having a semiconductor switching element in one of upper and lower arms and a diode in the other one, the second converter cell being configured to output positive-polarity and negative-polarity voltages corresponding to a magnitude of both-end voltage of the DC capacitor,
• when short-circuit between the DC lines is detected, the control device performs protection control to turn off the semiconductor switching elements in the power converter, and
• when elimination of the short-circuit between the DC lines is detected, the control device performs restart control of the power converter by giving a voltage command value for causing negative-polarity current flowing through the diode to flow to the phase arm, to each converter cell in the first arm and the second arm.