To suppress an increase in the input voltage of a regenerative converter on power recovery by stopping operation of a first switching element and the regenerative converter on the power failure of a main power supply, and at the same time by turning off a second switching element until the output voltage of a rectifier is set after the power recovery.
A main supply voltage being detected by a transformer 14 for detecting the main supply voltage is inputted into a rectifier REC, thus resulting in an output v1. When the v1 becomes lower than the partial pressure voltage of resistors R1 and R2, a comparator COMP changes an output v2 from H to L level. Since a monomulti MULT generates an L-level voltage with a specific time width at a leading edge of the v2, an output v3 of an AND gate AND is set to L level only for a specific period during power failure and power recovery. Also, the output v3 is connected as the stop signal of a chopper-controlling device 15 and a converter-controlling device 17, and becomes the gate signal of an IGBT6 via an insulation amplifier I-AMP and an on/off-controlling device 19.
OO NORIO
TACHIKAWA MAKOTO
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