| 摘要 |
PURPOSE:To dispense with a braking thyristor, by controlling to an open state only a combination of gate cut-off photocouplers which are provided in the gate circuits of triode AC switches for controlling the primary voltage of the three-phase induction motor and through which a direct current can be caused to flow. CONSTITUTION:In phase constriction and in braking, photocouplers 9R2, 9S1, 9S2, 9T1 are turned on to cut off the gates of triode AC switches. In driving and in braking, other photocouplers 9R1, 9T2 are turned off by a transistor 12 controlled by a braking controller 8, not to cut off the gates of triode AC switches. For that reasons, the triode AC switch 2R is turned on through a trigger diode 3R only in a direction from a power source toward a load. The other triode AC switch 2T is turned on through a trigger diode 3T only in a direction from the load toward the power source. As a result, a braking direct current flows through the phase R of the power source, the triode AC switch 2R, the phase U of the three-phase induction motor 1, its other phase W, the other triode AC switch 2T and the other phase T of the power source in that order to perform DC braking. |
