Method for protecting direct current line transient short-circuit fault of modular multiple-level converter

The invention relates to a method for protecting a direct current line transient short-circuit fault of a modular multiple-level converter, belonging to the technical field of direct current transmission. A group of two-way thyristor switch is connected on alternating current ports of each power unit of the modular multiple-level converter in parallel, when a direct current line has a transient short-circuit fault, control pulses of all of the power units are closed, and all of the two-way thyristor switches are triggered to be switched on at the same time, so that the short-circuit point of the direct current line is in natural arc extinction and disappears. When short-circuit current of the direct current line is detected to be zero, all of the two-way thyristor switches are controlled to be switched off, and the control pulses of all of the power units are opened, so that the converter runs again. With the adoption of the method, a switch device of the converter can be quickly protected from damage during a failure, and the direct current short-circuit point is in the natural arc extinction after failure, therefore, the device can automatically run again, thereby avoiding the complete off-stream of the device and greatly improving the reliability and the availability factor of the device.