Multi-terminal DC power grid reclosing method and system based on waveform similarity matching

Abstract

The invention relates to a multi-terminal DC power grid reclosing method and system based on waveform similarity matching, and the method comprises the steps: carrying out derivation calculation on power parameter measurement values at protection parts at two sides of a fault line based on a Bergeronmodel, and carrying out intersection to obtain power parameter theoretical values at the protection parts at two sides of the fault line; correspondingly obtaining the theoretical waveforms and true values of the line-mode traveling waves at the protection positions at the two sides of the fault line based on Karrenbauer transformation; based on a Hausdroff distance calculation method, carrying out quantitative calculation on the similarity between the real waveform and the theoretical waveform of the line-mode traveling waves at the protected parts at the two sides of the fault line; and determining the fault type of the internal fault according to the similarity between the real waveform of the line mode traveling wave and the theoretical waveform of the line mode traveling wave. According to the method, the type of the fault is judged based on the topological structure difference of the line under the permanent fault and the instantaneous fault and the similarity characteristic of the line mode currents on the two sides, and the problem that the fault properties of the remote fault and the high-resistance fault in the area cannot be recognized can be solved.

Description

technical field [0001] The invention relates to the field of power grids, in particular to a multi-terminal DC power grid reclosing method and system based on waveform similarity matching. Background technique [0002] Due to the great fluctuation and unpredictability of the supply of clean energy (such as wind energy, solar energy, tidal energy, etc.), it brings great difficulties to the centralized power transmission. The flexible DC technology based on fully-controlled switching devices can decouple active power and reactive power during power transmission without the risk of commutation failure, and can well deal with the problems caused by clean energy grid connection. Therefore, the proportion of clean energy is increasing today. Under the premise of increasing, the trend of new energy grid connection is gradually developing towards the multi-terminal DC grid structure. Today, the use of overhead lines has gradually become the future development trend of the multi-term...

AI Technical Summary

Problems solved by technology

However, this reclosing method has the following problems: if it recloses on a permanent fault, it will cause a second fault impact on the system

The typical method is as follows: Some experts proposed a new type of hybrid DC circuit breaker topology, which is suitable for the field of fast reclosing. In addition, some experts proposed to judge the nature of the fault by temporarily controlling the operation of the converter station in the uncontrolled rectification. This method requires a long restart time. Although this method is applicable to the two-terminal system, it is not applicable to the multi-terminal system; further, Some other experts proposed the method of adding additional control to the hybrid DCCB, through which the DCCB can inject pulse signals to detect faults, but this method needs to add additional devices, such as energy dissipation resistors and thyristors, etc., which makes the topology of the circuit breaker more complicated, and Increased engineering cost

The above methods all need to change the topological structure of the DC circuit breaker, the control mode of the converter station, and even add auxiliary control devices, which increases the cost of such methods and reduces the applicability.

[0005] Some experts have proposed a reclosing scheme that utilizes full-bridge MMC converters to actively inject characteristic signals. This scheme can flexibly convert the mode of injecting characteristic signals. However, this scheme is not applicable to the topology of half-bridge MMC converters. ; In addition, for DC lines with coupled DC circuit breakers, some experts proposed a characteristic signal injection method to identify the nature of the fault, but this injection method is only applicable to lines with coupled DC circuit breakers and is not universal; In addition, some experts have proposed a coincidence scheme that uses the half-bridge type MMC to actively inject traveling waves into the line to identify the nature of the fault. This scheme uses the difference in polarity of the reflected wave head of the traveling wave head under transient / permanent faults to design the criterion. High reliability, but limited by the sampling frequency, there will be a dead zone at the end of the line

[0006] To sum up, current reclosing schemes all rely on single-ended quantities to achieve, but the following problems generally exist: 1) Reclosing schemes are limited by the topology of DC circuit breakers or converters, and even need to add additional control devices. The cost of transforming the equipment involved in the system is high and the process is complicated, so it is not easy to promote; 2) The reclosing scheme that injects signals through the MMC converter does not require additional devices, but when a high-impedance fault occurs at the end of the line, the nature of the fault is difficult to distinguish. Risk of coincidence to permanent failure

Images