A Method for Evaluating the Impact of DC Grid Topology on Fault Current

Abstract

The invention discloses a method for evaluating the impact of the topology of a DC power grid on fault currents. First, the equivalent circuit of the grounding mode of the metal return line and the earth return line is established, and a three-dimensional mesh circuit diagram decoupling method is proposed, so that the equivalent circuit plane An improved high-frequency equivalent model was proposed, and fault current calculation methods were deduced for radial and ring networks, and the theory was extended to n terminal network, and then analyzed the influence of topology parameters and structure on fault current; proposed the evaluation index of topology influence on fault current k , which can effectively evaluate the impact of the initial fault current level on the grid topology; k The magnitude of the value determines which converter stations the DC grid unipolar short-circuit fault current mainly comes from at the initial stage. The evaluation method proposed by the invention avoids cumbersome calculations, and can directly and quickly evaluate the influence of the topology on the fault current.

Description

technical field [0001] The invention relates to the technical field of DC grid topology and fault current evaluation, in particular to a method for evaluating the influence of DC grid topology on fault current. Background technique [0002] Multi-terminal flexible DC grid has become a research hotspot due to its advantages of low harmonics, high reliability, and easy expansion. In actual engineering, single-pole ground fault events occur most frequently. After a unipolar ground fault occurs in a true bipolar system, the sub-module discharges rapidly and injects a large amount of surge current into the fault point. The outlet voltage of the converter station drops rapidly, and the bridge arm current and line current rise sharply, seriously threatening the safe and stable operation of the power grid. . Therefore, it is of great significance to study the influence mechanism of topology on unipolar fault current and the influence of topology parameters on fault current for pow...

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Problems solved by technology

[0005] Specifically, the multi-terminal true bipolar system equivalent circuit is established as in prior art 1, [References: Y.Li, J.Li, L.Xiong, X.Zhang and Z.Xu, "DC fault detection in meshed MTdc systems based on transient average value of current,"IEEE Trans.Ind.Electron.,vol.67,no.3,pp.1932-1943,Mar.2020.], its shortcoming is only for double-ended converter station DC transmission system, Not suitable for topology studies

[0006] Such as prior art 2 state space equation calculation method of fault current [reference 1: C.Li, C.Zhao, J.Xu, Y.Ji, F.Zhang and T.An, "A pole-to-pole short- circuit fault current calculation method for dc grids,"IEEE Trans.Power Syst.,vol.32,no.6,pp.4943-4953,Nov.2017; Reference 2: Lanxi Tang, Xinzhou Dong. MMC DC Transmission Grid Line Short Circuit Approximate calculation method of fault current [J]. Chinese Journal of Electrical Engineering, 2019, 39(02): 490-498+646.], its shortcoming is that only time-domain numerical results can be obtained and no explicit expression of fault current can be obtained formula, making it difficult to analyze the influencing factors of the fault current

[0007] Existing technology 3 analyzes the variation of various characteristic quantities of unipolar faults under the grounding mode of metal return lines, [References: Zhu Taoyan, Hou Yuanwen, Wang Chao, Chen Weihua. Operation mode of unipolar metal return lines in direct current transmission systems Research on ground fault and protection of lower line[J]. Power System Protection and Control, 2009,37(20):133-138] Its shortcomings do not deeply discuss the influence of topology structure and topology parameters on fault current, and do not propose to evaluate the impact of topology on fault current. Indicators of current influence

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