Electric power converting device and electric power converting method

An electric power converting method used for an electric power converting device which comprises:

• a converter which converts a three-phase AC voltage output from a three-phase AC power source, into a DC voltage of each phase of a three-phase AC load;
• an inverter which comprises a plurality of neutral-point-clamped (NPC) legs per phase and converts the DC voltage converted by the converter, into a single-phase AC voltage of each phase of the three-phase AC load;
• and
• a capacitor which is connected to a terminal between the converter and the inverter, and wherein
• the converter comprises for each phase of an electric power system a circuit which consists of a plurality of switching elements connected in series,
• the electric power converting method comprising:
• controlling, for each phase of the electric power system, on/off of a switching element corresponding to one of phases of the electric power system in the converter such that a voltage which reduces fluctuation of a DC voltage applied between the converter and the inverter and corresponding to each phase of the three-phase AC load is output from the converter.