| 摘要 |
PURPOSE:To lower the dielectric strength of a thyristor and capacitor and eliminate the necessity for measuring a capacitor voltage, by turning off a thyristor switch synchronously to a point of time when no overvoltage is impressed upon the capacitor in case the thyristor switch is wrongly ignited. CONSTITUTION:When a thyristor switch is wrongly ignited, a large rush current IC flows to a capacitor 3 and, therefore, a capacitor voltage VC has an overlapped waveform of a free vibration and AC voltage. Since the capacitor voltage VC becomes a value which approaches a supply voltage E at the time when the free vibration component and supply voltage component of the capacitor voltage VC become to have opposite polarity, the overvoltage of the thyristor switch 4 and capacitor 4 can be avoided if the thyristor switch 4 is turned off at this phase. In this way, the turning off time of the thyristor 4 can be detected without measuring the capacitor voltage. Therefore, a large-scaled measuring circuit is not required. |
