基于相空间暂态映射轨迹的复杂多端柔直配电网单极接地保护

doi:10.19595/j.cnki.1000-6753.tces.260051

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Abstract

Driven by the strategic goals of "carbon peaking and carbon neutrality," the growing integration of diversified DC loads is accelerating the evolution of distribution networks toward flexible DC systems. Flexible DC distribution, characterized by large transmission capacity and flexible power flow control, has emerged as a key technological pathway for building new-type power systems. However, fault transient characteristics are deeply coupled with converter control strategies, resulting in an extremely short available data window, and multi-terminal complex network topologies significantly increase the difficulty of fault identification. Existing protection schemes face three major challenges: (1) Excessive dependence on boundary components, such as current-limiting reactors, limits the applicability of existing protection schemes in multi-terminal meshed structures where boundaries are weak or absent; (2) Conventional directional criteria are disturbed by transient oscillations and nonlinear waveform distortions, degrading the performance of waveform correlation-based identification methods; (3) In neutral ineffectively grounded systems, the single-pole-to-ground fault current is inherently weak, exhibiting strong nonlinearity and non-monotonic characteristics, which makes fault identification extremely difficult.
To address these challenges, this paper first conducts an in-depth analysis of the single-pole-to-ground fault mechanism in complex multi-terminal flexible DC distribution networks. Considering the different grounding configurations of multiple converter types—including MMC, VSC, and DCT—and based on the "virtual breaking point" theory, the short-circuit current expressions under different fault scenarios are systematically derived, and the transient characteristic differences between internal and external faults are clearly identified. Subsequently, breaking through the limitations of traditional time-domain analysis, the fault current signal is mapped into a two-dimensional phase space. The single RLC-dominant response exhibits regular concentric shrinking ellipses due to time-delay orthogonality, while the multi RLC-superimposed response presents chaotic trajectories due to the destruction of orthogonality. Based on these significant geometric morphological differences, dual criteria of "initial quadrant distribution" and "principal axis offset" are constructed, and a single-pole-to-ground protection method based on phase-space transient mapping trajectory is proposed. Finally, simulation validation is conducted in PSCAD/EMTDC on a 10 kV six-terminal flexible DC distribution network model.
The conclusions can be drawn as follows: (1) Considering the virtual breaking point location and grounding configurations of multiple converter types, the time-domain transient signals of internal and external faults may exhibit similar characteristics in both amplitude and direction under different scenarios. For internal faults with the virtual breaking point K located on the fault line and external faults with K located on other lines, the currents on both sides are in opposite directions. For internal faults with K located on a non-fault line and external faults with K located on other lines, both exhibit multi-RLC superposition characteristics. (2) In the high-dimensional phase space, the single RLC-dominant response exhibits regular concentric shrinking ellipses due to time-delay orthogonality, while the multi RLC-superimposed response presents chaotic trajectories. By characterizing the phase-space trajectory features with initial quadrant distribution and principal axis offset, dual criteria are constructed to achieve reliable fault identification. (3) The proposed method does not rely on boundary components, is less affected by noise, does not require strict signal synchronization, and can withstand transition resistance up to 200 Ω.

Key words： Flexible DC distribution network single-pole-to-ground fault phase space reconstruction principal axis deviation weak-characteristic fault

Received: 11 January 2026

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TM77

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	Dai Zhihui
	Li Hanwei
	Shi Chen
	Hui Tianyi

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Dai Zhihui,Li Hanwei,Shi Chen等. Single-Pole Ground Fault Protection for Complex Multi-Terminal Flexible DC Distribution Networks Based on Phase Space Transient Mapping Trajectory[J]. Transactions of China Electrotechnical Society, 0, (): 260051-.

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