Flexible direct-current short-circuit fault protection method based on thyristor chain and superconducting current limiters

Abstract

The invention discloses a flexible direct-current short-circuit fault protection method based on a thyristor chain and superconducting current limiters. A converter used in a flexible direct-current power transmission system is a modularized multi-level converter cascaded based on half-bridge sub-modules and is of an A-B-C three-phase structure, and each phase comprises an upper bridge arm and a lower bridge arm; each bridge arm consists of a plurality of half-bridge sub-modules and a bridge arm inductor; an alternating current side output port of the modular multilevel converter is connected in parallel with the thyristor chain; the three-phase lines of the AC side of the modular multilevel converter are each connected in series with a superconducting current limiter; the upper ends of the three-phase upper bridge arms of the modular multilevel converter are connected to a direct current side through a first mechanical switch after being short-circuited, and the lower ends of the three-phase lower bridge arms are connected to the direct current side through a second mechanical switch after being short-circuited. According to the protection method, alternating-current and direct-current side current isolation under a fault condition is achieved by turning on the thyristor chain, the direct-current side fault current is reduced to zero, the alternating-current side fault current is limited through the superconducting current limiters, and therefore direct-current short-circuit fault protection of the flexible direct-current power transmission system is achieved.

Description

technical field [0001] The invention belongs to the technical field of multilevel power electronic converters, and in particular relates to a flexible DC short-circuit fault protection method based on a thyristor chain and a superconducting current limiter. Background technique [0002] The Modular Multilevel Converter (MMC) is composed of multiple sub-modules with the same structure cascaded. By adjusting the number of cascaded sub-modules, the voltage and power level can be changed, and any level of power can be realized. output, thereby effectively reducing the harmonic component of the output voltage, reducing the switching frequency and loss of the power switching device. MMC, with its high efficiency, easy expansion, easy redundancy design and many other advantages, has shown its important engineering application prospects in high-voltage and high-power systems, and is gradually being applied to renewable energy grid-connected, motor drives, and rail transit. and othe...

AI Technical Summary

Problems solved by technology

[0003] When a short-circuit fault occurs on the DC side of the MMC, due to the presence of freewheeling diodes in the half-bridge sub-modules, an uncontrolled rectification path will be formed. After each sub-module is blocked, the current on the AC side will feed current to the short-circuit point on the DC side through the freewheeling diodes. , will bring great harm to converters and transmission lines

In addition, in the traditional fault handling method, since the AC and DC sides are not isolated, the DC side current cannot be self-interrupted. Therefore, DC circuit breakers are often used to break the DC side fault current, which affects the breaking capacity of the DC circuit breaker. High requirements and high cost

In some fault handling methods that isolate the AC and DC sides, due to the direct short circuit on the AC side, the current on the AC side will increase sharply during faults, which is dozens of times that during normal operation, which will seriously endanger the safe operation of the power grid.

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