Power conversion device

A power conversion device connected to an AC power system, the power conversion device comprising:

• a power converter comprising a plurality of arms;
• and
• a control device to control the power converter, wherein
• each arm comprises a plurality of cascaded converter cells,
• each of the converter cells comprises:
• a pair of input and output terminals;
• a plurality of semiconductor switching elements;
• and
• a power storage element connected to the pair of input and output terminals with the plurality of semiconductor switching elements being interposed,
• the control device comprises:
• a first generator to generate a first voltage command value based on a positive-phase current command value and an inputted reverse-phase current command value for control of an AC current outputted from the power converter;
• a second generator to generate a second voltage command value for suppression of imbalance of voltages of power storage elements among the plurality of arms;
• a gate signal generator to generate a gate signal for control of on and off of the plurality of semiconductor switching elements in each converter cell based on the first voltage command value and the second voltage command value;
• and
• a reverse-phase voltage compensator to generate the reverse-phase current command value to compensate for a reverse-phase component contained in an AC voltage of the AC power system and to output the reverse-phase current command value to the first generator when reverse-phase voltage compensation is performed, and
• when a state in which imbalance of the AC voltage of the AC power system is determined as being minor based on comparison of an assessment value relating to a degree of the imbalance with a threshold value continues for a certain time period or longer, the reverse-phase voltage compensator performs the reverse-phase voltage compensation.