JP2928264B

An improved electric power conversion system comprising a multi-phase bridge circuit (3) is composed of semiconductors such as thyristors (TY1...TY6) and an associated firing circuit (31). It is so constructed that: if the AC input current Iac flowing in said bridge circuit (3) is equal to or larger in value than the DC output current Idc flowing out of the bridge circuit, it will be decided that an inner defect or fault is caused, and possible expansion of inner defect will be prevented by disabling the firing circuit (31) to extinguish said thyristors in the bridge circuit, and if the AC input current Iac is smaller than the DC output current Idc in value, the bridge (3) is permitted to continue the operation of power conversion, thus eliminating unnecessary interruption which otherwise would be caused by exterior disturbances. Also, an improved electric power conversion system may be equipped with a device to prevent an adverse effect from being caused by abnormal rise of thyristors' temperature.