Ac switch, and uninterruptible power supply and voltage sag compensator including ac switch

An uninterruptible power supply comprising a conversion device feed circuit and a bypass feed circuit, so that the uninterruptible power supply feeds power to a load by switching between the conversion device feed circuit and the bypass feed circuit,

• the conversion device feed circuit including
• a converter that converts AC power from an AC power source into DC power,
• an inverter that converts DC power outputted from the converter into AC power,
• a switch connected between an AC output terminal of the inverter and the load, and
• a storage device connected to a DC circuit between the converter and the inverter,
• the bypass feed circuit including an AC switch connected between the AC power source and the load,
• the uninterruptible power supply further comprising:
• a controller that turns on the AC switch and opens the switch, so as to switch a feed path from the conversion device feed circuit to the bypass feed circuit;
• and
• a current detector that detects an AC current supplied from the bypass feed circuit to the load,
• the AC switch including
• a first thyristor having an anode connected to the AC power source, and a cathode connected to the load,
• a second thyristor connected in antiparallel to the first thyristor between the AC power source and the load,
• a third thyristor having an anode connected to the AC power source, and a cathode connected to the load, and
• a fourth thyristor connected in antiparallel to the third thyristor between the AC power source and the load, wherein
• when the bypass feed circuit feeds power to the load, the controller causes the first thyristor and the third thyristor to conduct alternately and causes the second thyristor and the fourth thyristor to conduct alternately, for each one-cycle period of the AC current, in accordance with a detection value from the current detector.

A voltage sag compensator that feeds power to a load at a time of instantaneous voltage drop or instantaneous power failure of an AC power source, the voltage sag compensator comprising:

• an AC switch connected between the AC power source and the load;
• a storage device;
• an inverter that converts DC power outputted from the storage device into AC power;
• a controller that turns off the AC switch so as to switch a feed path from the AC power source to the inverter at the time of instantaneous voltage drop or instantaneous power failure of the AC power source, and
• a current detector that detects an AC current supplied from the AC power source to the load at a normal time of the AC power source,
• the AC switch including
• a first thyristor having an anode connected to the AC power source, and a cathode connected to the load,
• a second thyristor connected in antiparallel to the first thyristor between the AC power source and the load,
• a third thyristor having an anode connected to the AC power source, and a cathode connected to the load, and
• a fourth thyristor connected in antiparallel to the third thyristor between the AC power source and the load, wherein
• at the normal time of the AC power source, the controller causes the first thyristor and the third thyristor to conduct alternately and causes the second thyristor and the fourth thyristor to conduct alternately, for each one-cycle period of the AC current, in accordance with a detection value from the current detector.