Single-terminal protection method and system for multi-terminal direct current system based on transient current variance

Abstract

The invention discloses a single-terminal protection method and system for a multi-terminal direct current system based on transient current variance. The method comprises the steps of determining a sampling window of a protection method according to system parameters based on the principle that the sensitivity of the protection method is as high as possible and the transient variance current error is as small as possible for the multi-terminal direct-current system; setting a protection threshold according to system parameters and the length of the sampling window on the basis of ensuring selectivity; and extracting the high-frequency energy of the current signal based on the transient variance, if the high-frequency energy is greater than the protection threshold, judging an internal fault and executing a protection action, and if the high-frequency energy is less than the threshold, not executing the protection action. The method does not depend on simulation, the high-frequency component of the electric quantity is extracted through simpler calculation, the analytical solution of the protection threshold can be theoretically calculated, the selectivity of the protection method is ensured, the external noise resistance is high. The method has high sensitivity and good transition resistance resistance.

Description

technical field [0001] The invention belongs to the field of electric power technology, and in particular relates to a method and system for single-ended quantity protection of a multi-terminal DC system based on transient current variance. Background technique [0002] In recent years, multi-terminal DC systems connected to offshore wind energy have received extensive attention. For DC line faults, two-level voltage source converters (two-level voltage source converters, TLVSCs) and half-bridge modular multilevel converters (half-bridge modular multilevel converters, HBMMCs) lack control capabilities, resulting in The insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT) of the converter is quickly blocked, and the power transmission of the entire DC system is forced to be interrupted. With the development of power electronic DC circuit breaker (DC circuit breaker, DCCB), the DC fault can be cut off within a few milliseconds after the fault occurs, av...

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Problems solved by technology

[0004] 1. Lack of analytical expression of fault current suitable for multi-terminal DC grid;

[0005] 2. The sampling rate of the protection method is high, and the calculation amount of the protection method is relatively large;

[0007] 4. The protection method is easily affected by external noise and has a poor fault tolerance rate

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