DC Fault Judgment Method and Control Method for Multi-terminal Flexible DC Transmission System

Abstract

The invention discloses a DC fault judgment method for a flexible multi-terminal DC transmission system. The DC rise rate in a DC fault is lowered by increasing a DC inductance value to prevent an MMC from being locked; or an AC instruction value of the MMC is set to be zero during the DC fault, so that a bridge arm current is lowered to prevent the MMC from being locked; or the MMC is locked during the DC fault, but an AC breaker of the MMC is not cut off, so that the power restoration speed after the fault is cleared is improved. The invention further discloses the DC fault judgment method for the flexible multi-terminal DC transmission system. The DC voltage mutation rate on a DC inductance line side is measured, so that the DC fault is judged when an absolute value of the mutation rate exceeds a certain threshold. The AC breaker of the MMC can be prevented from being cut off in the DC fault; the power restoration speed of the MMC employing an overhead line after the DC fault is cleared is greatly improved; meanwhile, a rapid and accurate judgment can be made for the DC fault; and timely fault treatment and control are facilitated, so that the risk that the MMC bears an over-current is reduced.

Description

technical field [0001] The invention belongs to the technical field of power transmission and distribution in power systems, and more specifically relates to a DC fault judgment method and control method for a multi-terminal flexible DC power transmission system. Background technique [0002] With the development of the Modular Multilevel Converter (MMC), the Modular Multilevel Converter has been increasingly used in direct current transmission. Most existing MMCs use half-bridge sub-modules. When a DC fault occurs, it is necessary to block the trigger pulse of the IGBT (Insulated Gate Bipolar Transistor, insulated gate bipolar transistor) to prevent the sub-module capacitor from being discharged through the IGBT, thereby damaging the IGBT due to overcurrent. . After the IGBT is locked, the MMC works in an uncontrolled rectification state. The AC system connected to the MMC continuously provides fault current to the DC fault point through the diode. Breaking the AC circuit...

AI Technical Summary

Problems solved by technology

Due to the need to compare the physical quantities on both sides of the line, the conventional fault judgment method needs to rely on the communication system, and the communication system will bring a delay. During this delay, the DC fault current will continue to rise, making the MMC more susceptible to overcurrent. In order to reduce Overcurrent requires a faster DC fault judgment method

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