| 摘要 |
PURPOSE:To exactly prevent the overvoltage of snubber diodes from being generated along with the recovery of counter recovery current, by making the voltage of a DC power source discharged from a condenser, higher than the voltage of the DC power source of an inverter, always or temporarily. CONSTITUTION:When the voltage Vx of auxiliary DC power sources 31-34 is compared with the voltage V1 of the generation of distribution inductance between a semiconductor switch and a DC power source 1, then the voltage Vx is set so that Vx>V1 may be shown. When reflux working is performed in the ON-state of semiconductor switches 2, 4 and in the OFF-state of semiconductor switches 3, 5, then snubber diode 21 is kept in an OFF-state. Even if the semiconductor switch 4 is turned OFF and the semiconductor switch 5 is turned ON, the counter recovery current of the snubberr diode 21 hardly flows to the switch 5, and the counter-directional overvoltage of the terminal of the snubber diode 21 is not generated. Said working is found in the same manner also on other snubber diodes 18-20.
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