Power conversion device

A power conversion device comprising:

• a power converter for performing power conversion between three-phase AC, and DC, the power converter including a plurality of leg circuits each having a positive arm and a negative arm connected in series, outputs of the positive arm and the negative arm being connected to each phase AC line, the plurality of leg circuits being connected in parallel between positive and negative DC buses;
• and
• a control device for controlling the power converter, wherein
• each of the positive arm and the negative arm of each leg circuit is composed of one or a plurality of converter cells connected in series and including:
• a series unit of a plurality of semiconductor switching elements connected in series to each other;
• and a DC capacitor connected in parallel to the series unit,
• the control device includes a voltage command generating unit for generating a first voltage command for the positive arm and a second voltage command for the negative arm, to perform output control for each converter cell in the positive arm and the negative arm by PWM control,
• the voltage command generating unit includes:
• an AC current control unit for generating an AC control command for controlling an AC current component flowing through each phase AC line;
• a circulating current control unit for calculating a circulation control command for controlling a circulating current component for each phase which circulates between the leg circuits;
• and a command distributing unit for determining the first voltage command and the second voltage command on the basis of the AC control command, the circulation control command, and a voltage command value for voltage between the DC buses,
• the circulating current control unit includes:
• a compensator for calculating a first control command so that circulating current for each phase which circulates between the leg circuits approaches a circulating current command value;
• and a suppression unit for generating a second control command for suppressing at least one of a double-frequency component and a quadruple-frequency component of an AC fundamental wave, which are contained in the calculated first control command, and
• the circulating current control unit calculates the circulation control command by combining the first control command and the second control command.