| 摘要 |
PURPOSE:To detect exactly a fault even in case there is no output of an invertor by connecting a rectifier in parallel between an invertor of a pulse width modulating system and a load, and detecting a voltage level through a smoothing capacitor, etc. CONSTITUTION:A load 8 of an induction motor, etc. is driven by an invertor 18 of a pulse width modulating system. The output of a rectifier 19 connected in parallel to this invertor 18 is smoothed through a smoothing capacitor 20 of a discharge time constant which is longer than a charge time constant and the period of a pulse width modulated wave. When the output of the invertor 18 is reduced to zero, the capacitor starts a discharge, its output voltage drops, a DC relay 21 for forming a detecting circuit goes to a non-energized state, and it can be detected exactly that the output of the invertor is gone.
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