基于虚拟电抗的双馈风场接入柔直系统交流线路保护方案

doi:10.19595/j.cnki.1000-6753.tces.242337

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Abstract

With the rapid development of renewable energy in central and western China, the flexible DC system has become a widely adopted solution for long-distance, large-scale power delivery. These systems offer high flexibility and reliability. When doubly-fed induction generator (DFIG) based wind farms are integrated into a flexible DC system, the fault response deviates significantly from those of traditional AC systems, especially weak infeed features characterized by low fault current and ambiguous direction. As a result, conventional protection methods based on power-frequency are prone to both maloperation and failure to operate. Therefore, there is an urgent need for a reliable protection scheme suitable for DFIG-based wind farms integrated into a flexible DC system. To address the above issues, this paper proposes a pilot protection scheme based on virtual reactance difference.
Firstly, an equivalent model of the DFIG with low-voltage ride-through (LVRT) control is built. A converter model considering control dynamics is also developed. These models represent the actual response of the DFIG-based wind farms integrated into a flexible DC system during faults. By considering the control strategies of converters and the LVRT behavior of DFIGs at both ends of the AC line during faults, this work improves the accuracy of modeling and enhances the applicability of the proposed scheme in DFIG-based wind farms integrated into a flexible DC system.
Secondly, based on the fault equivalent network, virtual reactance expressions at both ends of the AC line are derived for different fault scenarios. The results reveal distinct differences in virtual reactance between internal and external faults. A high-speed protection criterion is designed using the variance of the virtual reactance at both terminals. The paper also proposes a frequency selection principle for the protection scheme, in which the angular frequency corresponding to the maximum difference in virtual reactance between internal and external faults is selected as the frequency for extracting electrical quantities by the protection device.
Finally, the proposed scheme is tested on the RT-LAB hardware-in-the-loop simulation platform. The results demonstrate that the proposed protection scheme can accurately identify internal and external faults. It also exhibits advantages such as high resistance tolerance, low communication requirements, and high sensitivity.
The conclusions can be drawn as follows: (1) The virtual reactance at both terminals of an AC line shows significant differences under internal and external faults. This distinction forms a solid theoretical foundation for fault discrimination and enhances fault identification reliability. (2) The proposed method uses this feature to build a practical pilot protection scheme. It does not rely on power-frequency quantities or high synchronization accuracy. This improves the adaptability of protection under weak fault current infeed. (3) The method provides a reliable solution for AC line protection in DFIG-based wind farms integrated into flexible DC system.

Key words： DFIG-based wind farms flexible DC system AC line protection pilot protection

Received: 23 December 2024

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TM77

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	Ma Jing
	Wu Yilin
	Xu Guojie
	Zhao Yufeng

Cite this article:

Ma Jing,Wu Yilin,Xu Guojie等. A Virtual Reactance-based AC Line Protection Scheme for DFIG-based Wind Farms Connected to a Flexible DC System[J]. Transactions of China Electrotechnical Society, 0, (): 258102-258102.

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