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

Abstract

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.

Description

technical field [0001] The invention relates to a protection method for instantaneous short-circuit fault of a DC line of a modular multi-level converter, in particular to a protection method for a short-circuit fault in a flexible direct current transmission system based on a modular multi-level converter, which belongs to direct current transmission technology field. Background technique [0002] Flexible DC transmission is based on voltage source converter and pulse width modulation technology to invert DC voltage into AC voltage with controllable amplitude and phase, and can independently and quickly control the transmitted active power and reactive power, which greatly enhances the Transmission flexibility. The modular multilevel converter does not require direct series connection of switching devices, and can obtain excellent harmonic performance and loss performance through multilevel technology. It is a voltage source converter with the most application potential in...

AI Technical Summary

Problems solved by technology

However, since the converter is already in an uncontrolled rectification state after the short-circuit fault, there is still a DC voltage applied to the short-circuit point after rectification, resulting in the short-circuit point being unable to extinguish the arc

Even if the external factors causing the instantaneous short circuit disappear, the short circuit current will not disappear, making fault protection very difficult

At present, in the case of an instantaneous short-circuit fault on the DC line, the short-circuit current can only be cut off by disconnecting the AC circuit breaker and disconnecting the converter from the AC grid.

However, the disconnection of the AC circuit breaker also means the complete outage of the flexible DC transmission system, which requires a relatively complicated manual operation process before it can be put into operation again, resulting in a long-term outage of the DC transmission system, resulting in power transmission losses, and The reliability and availability of the flexible direct current transmission system are greatly reduced

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