| 摘要 |
PROBLEM TO BE SOLVED: To prevent the overvoltage of an output voltage, by simultaneously applying a continuous gate pulse to the thyristor of in-phase, high- and low- pressure side arms for 1/4 cycles or more on stop, and by allowing a DC current to circulate. SOLUTION: When an operation circuit 51 outputs a stop signal 51-1, a gate control circuit 44 outputs a signal of an arbitrary period, which is inputted to OR circuits 421 and 431, and a gate pulse is simultaneously fed to thyristors 11 and 12 of in-phase, high and low voltage side arms. At this time, when the stop signal 51-1 is generated for a period while a DC voltage is negative, the thyristor is not ignited, thus requiring the output of a gate control circuit 44 of 1/4 cycles or more. Then, when the DC voltage becomes positive, the thyristors 11 and 12 are ignited, the current circulates according to a loop of a DC reactor 4-the thyristor 11 and the thyristor 12-a DC current transformer 6-a thyristor current transformer, and an output current to a capacitor 21 is disconnected and attenuated, thus preventing the overvoltage of an output voltage on stop. |
