有效消纳各种新能源的微电网技术有助于提高能源利用效率、增强系统韧性，在“双碳”目标中扮演重要角色，然而其多能源集成、运行方式灵活的特性也提升了微电网线路保护的复杂度。行波保护因不受微电网运行方式影响且具有快速识别故障的能力在微电网线路保护中应用具有突出优势。现有微电网行波保护多着眼于故障行波初始波头信息，但此方法极易受到初始波头信息识别和捕获精度的影响而发生保护误动或拒动的问题。因此，本文针对以上问题，提出行波时域波形特征的微电网线路保护方法，以实现对微电网线路可靠有效的保护。主要研究内容如下：

       首先，分析微电网系统结构及运行特点，梳理现有保护存在的缺陷，从原理上说明行波在微电网中的产生与传播过程，获取折、反射系数计算表达式；在此基础上，建立微电网行波一模分量等值电路，推导出微电网发生区内、外故障时线路两端的前、反行波时域表达式，得出微电网线路行波时域波形特征，为行波保护方法提供理论支撑。

       其次，根据微电网故障行波时域波形特征，提出行波时域波形余弦相似度的微电网线路主保护方法。通过计算微电网线路区内、外故障下前、反行波信号的余弦相似度系数来准确识别故障，克服了传统方法波头提取困难所导致的误动和拒动的问题；设计微电网线路主保护流程以及实现系统，确保系统可以准确可靠的识别故障。仿真结果表明在不同运行方式、不同故障类型及不同故障位置下保护均能可靠动作，证明了所提方法的有效性。

       最后，为应对微电网主保护发生拒动或断路器故障的情况，提出广域行波信息的微电网线路后备保护方法。通过构建微电网广域保护系统，设计广域后备保护构架；为降低通讯系统负担，提出基于节点出度的微电网故障分区算法，利用行波幅值积分比来识别故障区域，再通过前、反行波的余弦相似度对故障区段进行精准识别；制定微电网广域后备保护实现方案，确保后备保护系统的可靠运行。所提方法旨在解决现有微电网本地后备保护难以整定配合的问题，有利于提高保护的可靠性。算例分析和仿真验证表明此方法在微电网不同运行方式、不同故障位置及不同故障类型下，均能准确识别故障。

       The microgrid technology that effectively absorbs various renewable sources can help to improve energy utilization efficiency and enhance system resilience, playing an important role in the "dual carbon" goal. However, its multi energy integration and flexible operation characteristics also increase the complexity of microgrid line protection. Traveling waves protection has outstanding advantages in the application of microgrid line protection, as it is not affected by the operation mode of microgrid and has the ability to quickly identify faults. The existing microgrid traveling waves protection mainly focuses on the head information of initial wave of fault traveling waves, which may lead to protection misoperation or refusal to operate because of head information recognition and capture accuracy of initial wave. To this end, this thesis proposes a microgrid line protection method based on the time domain waveform characteristics of traveling waves to achieve reliable and effective protection of microgrid lines. The main research contents are as follows:

       Firstly, the structure and operational characteristics of the microgrid system are analyzed for identifying the shortcomings of existing protection methods. And the generation and propagation process of traveling waves in the microgrid from a theoretical perspective are explained to obtain expressions for calculating the refraction and reflection coefficients. On this basis, the 1-mode fault component equivalent circuit of microgrid is established to derive the time domain expressions of the forward and backward traveling waves at both ends of the line in case of internal and external faults. The time domain waveform characteristics of the traveling wave of the microgrid line are obtained, which provides theoretical support for the traveling waves protection method.

       Secondly, based on the time domain waveform characteristics of microgrid faults, a main microgrid line protection method using cosine similarity of time domain waveform of traveling waves is proposed. By calculating the cosine similarity coefficients of the forward and backward traveling waves signals under internal and external faults in the microgrid line area, faults can be accurately identified. The proposed protection method overcomes the problems of misoperation and rejection caused by the difficult head information extraction of traveling waves in traditional methods. The main protection process and implementation system for microgrid lines are designed to ensure the system can accurately and reliably identify faults. The simulation results show the effectiveness of the proposed protection method under different operating modes, fault types, and fault positions.

       Finally, to address the situation of main protection failure or circuit breaker failure in microgrid, a backup microgrid line protection method based on wide area traveling waves information is proposed. By constructing the wide area protection system of microgrid, the wide area backup protection framework is designed. For reducing the burden on communication systems, a microgrid fault zoning algorithm based on node out degree is proposed. The backup protection algorithm uses the integral ratio of traveling waves amplitude to identify the fault area, and then accurately identifies the fault section through the cosine similarity of the forward and backward traveling waves. A wide area backup protection implementation plan for microgrid is developed to ensure the reliable operation of the backup protection system. The proposed method solves the problem of difficulty in setting and coordinating backup protection in existing local microgrid, which is beneficial for improving the reliability of protection method. Case analysis and simulation verification show that the proposed method can accurately identify faults in microgrid under different operating modes, fault locations, and fault types.

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