| 摘要 |
During the normal process of opening a switch at zero currents, a high charge is trapped on the series capacitor C in the compensator. After a further half cycle the applied voltage and the capacitor voltage are additive imposing a voltage exceeding twice the peak system voltage on the switch such as a thyristor T. According to the invention, the compensator includes a current-limiting inductor L and control means arranged to perform a sequence of switching operations on the thyristor thereby to cause an at least partly discharged condition of the capacitor means to coincide with a zero-current state of the series circuit. Preferably, the thyristor is switched OFF at zero current, then ON after a delay, following which the capacitor resonates with the current-limiting inductor and, at a point at which the capacitor voltage is near zero and the current is near zero, the thyristor is switched OFF again, leaving little or no offset on the blocked thyristor voltage. The blocking sequence may include more than one opening and closing operation before the final opening operation at the coincidence point. The mode of operation of the compensator reduces stress on the switch. |
