| 摘要 |
PURPOSE:To offer an overvoltage preventing device by which excessive voltage is not generated in a semiconductor switching element by connecting a connecting point of each reactor and the semiconductor switching element to a common voltage clipping circuit through a diode, respectively. CONSTITUTION:When currents iA1, iA2 flowing to gate turn-off thyristors (GTO) 41, 61 are cut off at a time (to), voltages v1, v2 of the GTOs 41, 61 rise linearly to a time point t1 when they become clip voltage VM of a voltage clipping circuit 7, in case when a time constant of a load 2 is very large. In case of a semiconductor switching element, a voltage build-up rate dv/dt in said case is determined so as to become below a value set to its element. The voltages v1, v2 do not rise above VM, currents iS1, iS2 which have flowed into snubber capacitors 42, 62 before that time are reduced suddenly at the time t1, a current of iM flows into the clipping circuit 7, and after the time t1, energy of the load 2 and energy of current balancer reactors 3, 5 are absorbed by the voltage clipping circuit 7. |
