Multi-terminal flexible DC power line DC line protection method based on voltage pole waves

Abstract

The invention discloses a multi-terminal flexible DC power line DC line protection method based on voltage pole waves. According to the method, voltage response characteristics of a fault line and a non-fault line at the line boundary during the DC line fault are analyzed, a wavelet transform tool is utilized to extract the transient voltage pole wave characteristic quantity, and internal and external fault identification criteria based on voltage pole wave amplitude characteristics are constructed; for lightning stroke interference, lightning stroke identification criteria for a voltage polewave high and low frequency energy ratio are established; according to the voltage pole wave amplitude relationship of the two-pole line, fault pole identification criteria are constructed. Compared with other protection principles, the method is advantaged in that the motion speed is relatively fast, influence of lightning stroke disturbance is avoided, anti-transition resistance capability is relatively strong, and sensitivity is high.

Description

technical field [0001] The invention relates to the technical field of DC line protection of a multi-terminal flexible DC power grid, in particular to a method for protecting a DC line of a multi-terminal flexible DC power grid based on voltage polar waves. Background technique [0002] With the increasing proportion of distributed power generation and DC loads and the wide application of power electronic devices, the flexible DC power transmission and distribution system based on voltage source converters will become one of the mainstream trends in the development of the global energy Internet in the future. Among them, the multi-terminal flexible DC power grid is a research and application hotspot in the field of DC transmission. It realizes multi-source power supply and multi-drop power receiving, saves operating costs in the case of multi-converter stations, and has obvious advantages in power supply reliability and other aspects. For the multi-terminal flexible DC power...

AI Technical Summary

Problems solved by technology

[0004] The prior art uses wavelet transform analysis tools to propose a single-ended traveling wave protection scheme for multi-terminal flexible DC transmission lines, but less consideration is given to influencing factors such as transition resistance and fault location

[0005] The existing technology uses the idea of ​​traveling wave protection and boundary protection to propose a protection method for flexible DC transmission. The action speed is very fast, but its sensitivity is seriously affected by the transition resistance

[0006] The existing technology proposes an improved wave protection based on the polar wave change rate, and studies the influence of the sampling rate on the protection sensitivity. However, in order to ensure the sensitivity of the protection scheme, it requires a higher sampling rate.

[0007] The existing technology realizes rapid identification of faults inside and outside the zone through the boundary difference formed by the reactors between the lines, and uses the voltage differential characteristics. However, the DC lines of the flexible DC grid are easily affected by high-frequency interference signals such as lightning strikes and noise. This protection method Misoperation due to interference cannot be avoided

[0008] The prior art proposes a protection scheme that uses multiple single-ended quantities for fault discrimination, including wavelet coefficients of current and voltage and voltage differential. The protection reliability is high, but the algorithm is complex

[0009] The existing technology proposes an ultra-high-speed protection scheme for overhead lines based on the voltage change rate, the protection data window is only 0.25ms, and the protection speed is extremely fast, but the influence of lightning interference is not considered

[0010] The existing technology proposes a multi-terminal flexible DC transmission short-term energy protection scheme based on differential current, which has absolute selectivity, but because the protection uses the double-terminal quantity of the DC line for fault discrimination, the quick action of the protection is poor

[0011] It can be seen that the existing protection methods for the DC lines of the multi-terminal flexible DC grid have their own advantages and disadvantages, but there is no method with fast action speed, unaffected by transition resistance and lightning interference, and high sensitivity.

Images