Method for suppressing DC bipolar short-circuit fault current of modular multi-level converter system

Abstract

The invention discloses a method for suppressing a DC bipolar short-circuit fault current of a modular multi-level converter system. The method obtains a voltage value Usup to suppress a fault current according to calculation of margin based on modulation degrees and makes judgment of the fault current: (1) controlling the DC voltage as -Usup when the fault current is greater than the upper limit of current I1im; (2) controlling the DC voltage as Usup when the fault current is smaller than the lower limit of current -I1im; (3) controlling the DC voltage as zero when the fault current ranges between the upper limit and the lower limit wherein a system functions as two reactive power compensators connected in parallel and is capable of providing reactive support for a power grid. The method is capable of suppressing the fault current within a given range. The calculation of the method is simple and easy.

Description

technical field [0001] The invention relates to the technical fields of flexible power transmission and distribution of electric power systems, power electronics and user electric power, and in particular to a method for suppressing DC bipolar short-circuit fault current of a modular multilevel converter system based on hybrid connection of full bridge and half bridge. Background technique [0002] With the development of fully-controlled power electronic devices and the application of power electronic technology in power systems, the flexible DC transmission technology based on voltage source converters has been paid more and more attention. Modular multi-level converter is a kind of voltage source converter in the application of flexible direct current transmission system. It is composed of multiple sub-modules connected in a certain way. By separately controlling the input and disconnection status of each sub-module IGBT component Make the AC voltage output by the convert...

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Problems solved by technology

[0004] German scholar Rainer Marquardt introduced the full-bridge sub-module MMC topology with the ability to ride through severe DC faults. When a DC short-circuit fault occurs, the fault current can be suppressed by blocking the converter, but the system cannot provide reactive support for the grid after the system is blocked. The fault recovery time is longer, and at the same time, the construction cost of the converter is increased because the switching devices required by the full-bridge sub-module are twice that of the half-bridge sub-module

[0005] The paper "Sub-module Hybrid MMC-HVDC DC Fault Ride-Through Control Strategy" pointed out that when the number of half-bridge sub-modules in the bridge arm is equal to the number of full-bridge sub-modules, the fault current can be suppressed by introducing a virtual resistor. There is no need for blocking, and the reactive power demand of the AC system can be continuously guaranteed, but the determination of the virtual resistance shown in the article is cumbersome, and the current fluctuates greatly and is uncontrollable

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