A power converter includes two arms for each phase between DC terminals, and each arm is formed by connecting a plurality of converter cells in series. A control device includes an arm voltage command generation unit which generates, for each arm, an arm voltage command for the plurality of converter cells. The arm voltage command is generated by superimposing a zero-phase-sequence voltage command having a frequency component that is three times an AC fundamental frequency. Phase adjustment of the zero-phase-sequence voltage command is performed on the basis of voltage of a DC capacitor in the converter cell and the arm voltage command.