| 摘要 |
PURPOSE:To make an apparatus simple and cheap, by a method wherein shortcircuit detection of upper and lower arms is performed by comparing absolute value of output of AC side current detector and sum of a current detector installed within each arm. CONSTITUTION:A converter circuit converts AC power source 1 into DC by a converter comprising an AC reactor 2, GTO 3, 6-7, 10 and free wheeling diodes 4-5, 8, 9, and supplies it through a filter capacitor 11 to a DC load 12. Its control circuit is constituted by current detectors 13-15 for AC input current or the like, an absolute value detection circuit 16, an adder 17, a subtractor 18, and a level detector 19. If switching of the GTO is performed normally in this constitution, absolute value of the input current and summed value of outputs of the detectors 14-15 are equal, and output of the subtractor 18 is zero. However, if shortcircuit of the upper and lower arms is produced, this produces output to the subtractor 18 through the adder 17, and if the output becomes a certain value or more, protection operation command 20 is outputted from the level detector 19.
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