| 摘要 |
PROBLEM TO BE SOLVED: To prevent excess current and protect a semiconductor switch, even if there is a voltage difference due to a phase difference between an AC power supply and a converter, when the connection is switched over from the converter to the semiconductor switch by connecting in parallel the converter and a series circuit of the semiconductor switch an impedance. SOLUTION: In a swithcing circuit of an uninterruptible power supply which, being provided with a converter 13 which converts the output of an AC power supply 20 to a specified AC voltage and a semiconductor switch 14 connected in parallel to the converter 13, switches the connection between the converter 13 and the semiconductor switch 14 and supplies power to a load 30, an impedance 15 is inserted in series with the semiconductor switch 14. When there is a failure in the converter 13 the connection is switched to the semiconductor switch 14, excess current in the semiconductor switch 14 caused by capacitors 11, 12 which are different in voltage due to a phase difference is suppressed by the impedance 15. By this method, the semiconductor switch 14 can be protected from the damages due to excess current. |
