Fuji Electric Systems Co. Ltd.

Fuji Electric Holdings Co., Ltd.

Hirokazu Tokuda

Nobuyuki Kobayashi

Osamu Hashimoto

Yasuhiro Okuma

Hiroyuki Matsuo

A power conversion apparatus includes serially connected arms U and X, serially connected arms V and Y, serially connected arms W and Z, and a capacitor, the pairs of serially connected arms and the capacitor all connected in parallel to one another. The input-side arms U and X and the output-side arms W and Z are subjected to PWM control so that the arms W and Z are controlled to have a voltage that is lower than that of the arms U and X, thereby providing a step down operation. A step up operation also can be provided by an opposite relation in which the arms W and Z are controlled to have a voltage that is higher than that of the arms U and X, thereby to expand the range within which the output voltage is controlled with the effect of reducing distortion.

Power conversion apparatus

A power-supply device suppresses high harmonic waves, controls the flow of AC power, and minimizes adverse effects on a load that might otherwise be caused by a large surge of current into the load during the startup or stopping of the power-supply device. The power supply device includes a voltage supply unitdisposed in series between input and output terminals. This voltage supply unit functions to gradually lower the output-voltage level from a state of canceling the voltage across input terminals of the power supply device at the time of starting up the power-supply device, so that a gradual rise in the output voltage from the power-supply device is achieved. When the power-supply device is stopped, a gradual lowering of the output voltage from the power-supply device is obtained by gradually increasing the output voltage of the voltage supply unit so as to cancel the input voltage.

Power-supply device

An uninterruptible power supply system prevents an output voltage from dropping due to an operation delay of a relay for isolating an alternating-current power source side and avoids an unexpected current flowing between the alternating-current power source side and the uninterruptible power supply system side. When short circuit occurs, a parallel converter connected in parallel to input terminals connected to an alternating-current power source is made to operate so that the output voltage thereof becomes '0' or the input voltage Vin and a series inverter connected in series between an input relay and one of output terminals is made to carry out a compensating operation with a smoothing capacitor taken as a power source so that a value of an applied voltage to the output terminals becomes an output voltage command value Vout*. This makes the output voltage of the parallel converter become '0' or Vin to produce no electric potential difference between the alternating-current power source side and the output side of the parallel converter. Therefore, no current flows between the alternating-current power source side and the parallel converter, and a value of an applied voltage to the output terminals is to be continuously maintained at the output voltage command value Vout* by the series inverter.

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Tokyo, Japan

Hirokazu Tokuda