To provide an interruptible power supply system which uses a bidirectional inverter connected with a transformer for detecting voltage in which an overcurrent is prevented from flowing to the transformer when power is supplied to a load from a three-phase AC power supply.
Between a three-phase AC power supply 1 and a load 2, a DC power supply 3, a bidirectional inverter 4, and a transformer 7 are provided in parallel. The inverter 4 is composed of three pairs of half-bridge type switching circuits 12 whose virtual neutral point has an electric potential at an intermediate point of a direct current divided into two by a capacitor and an inverter control circuit 15 for controlling operation of the switching circuit 12. The secondary side of the transformer 7 is connected to the circuit 15 and the neutral point on the primary side is connected to the virtual neutral point. When the three-phase AC power supply 1 is abnormal, power is supplied by the DC power supply 3. A switch 16 is provided to a circuit connecting the virtual neutral point and the neutral point on the primary side of the transformer 7. The switch is turned OFF when power is supplied by the three-phase AC power supply and ON when power is supplied by the DC power supply.
DOBASHI MITSUO
MIYASAKA ATSUSHI
TANAKA YUKI
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