PURPOSE: To prevent the circulating current between the PWM converters of parallel uniterruptible power unit which shares an AC power source and a storage battery.
CONSTITUTION: A storage battery 4 is connected to the junction between the DC output end of a converter 9A and the input end of an inverter 10A, and diodes 11A and 12A are connected between the junction and the DC end of the converter 9A, and the polarity is put in the direction where DC power flows from the converter 9A to the inverter 10A. Moreover, the charge of the storage battery is performed with other power power source, and the charge voltage is set lower than the DC output voltage of the converter, and both poles of the storage battery 4 are provided with diodes 11A and 12A, and the polarity is put in the direction where the DC power flows to the inverter 10A. The DC biased magnetization of an AC reactor 51A, etc., is prevented, and heating can be avoided.
SHIRAHAMA HIDEFUMI
SHIMADA KEIZO
