随着我国经济持续快速增长，电力需求不断攀升，对电网的电能质量和供电可靠性提出了更高要求。电压暂降作为电力系统中难以避免的电能质量问题，不仅给用户的正常用电带来不便，也可能导致巨大的经济损失。因此快速精确定位电压暂降源和准确评估电压暂降事件的严重程度，对降低电压暂降的危害程度和提高供电可靠性具有重要意义。本文主要从电压暂降源定位与严重程度评估两方面进行研究，主要工作内容如下：

首先，本文提出了一种基于微型同步相量测量装置(Micro-Phasor Measurement Unit, μPMU)和二分搜索法的简单辐射状配电网电压暂降源精确定位方法。利用μPMU装置测的电压暂降期间的电压变化量计算暂降源电流。通过分别假设暂降源位于各个分层电路的各个母线节点计算末端母线电压变化量，依据末端母线电压计算值与实测值的误差大小定位暂降源。为实现电压暂降源的快速精确定位，提出采用二分搜索法快速精确定位电压暂降源。在Matlab对所提算法进行验证，结果表明本文方法对配电网中不同位置、不同类型的电压暂降源均有较高的定位精度。

其次，针对大规模配电网电压暂降源定位算法计算量相对较大的问题，提出基于配网分区等效的复杂辐射状配电网暂降源定位算法。先利用深度优先搜索算法寻找配电网最长通路并计算最长通路节点权重，结合配电网分区划分要求，将配电网划分为多个子分区，对各分区外电路采用等效阻抗等值。在分区等效的基础上假设暂降源位于各母线节点计算末端母线电压误差大小，依据误差大小确定暂降源临近母线所在分区与分层电路。利用二分搜索法快速精确定位电压暂降源。通过降低阻抗矩阵的阶数和分层电路包含的母线数，提高电压暂降源定位效率。经过IEEE-33节点算例仿真验证，基于配网分区等效的复杂辐射状配电网暂降源定位算法相比简单辐射状配电网暂降源定位算法定位精度不变，定位所需时间显著缩短。

最后，针对单次电压暂降事件建立了电网侧和设备侧的电压暂降严重程度评估指标，分别采用权值函数和能量指标函数从设备侧和电网侧对电压暂降事件的严重程度进行评估。针对非矩形波电压暂降，提出基于曲线拟合的电压暂降严重程度评估方法，运用最小二乘法拟合非矩形波电压暂降波形，利用拟合函数评估非矩形波电压暂降，提高了非矩形波电压暂降严重程度评估的准确性。通过对仿真得到的非矩形波电压暂降波形进行严重程度评估，验证了基于曲线拟合的非矩形波电压暂降严重程度评估方法计算简单高效，易于在工程上操作和实现，有较高的工程应用价值。

With the sustained and rapid growth of China's economy and the rising demand for electricity, higher requirements are placed on the power quality and power supply reliability of the power grid. As an unavoidable power quality problem in power system, voltage sag not only brings inconvenience to users' normal power consumption, but also may lead to huge economic losses. Therefore, it is of great significance to quickly and accurately locate the voltage sag source and evaluate the severity of voltage sag events to reduce the harm of voltage sag and improve the reliability of power supply. This paper mainly studies the voltage sag source location and severity evaluation. The main work contents are as follows:

Firstly, this paper proposes a precise positioning method of voltage sag source in simple radial distribution network based on Micro-Phasor Measurement Unit (μPMU) and binary search method. The voltage variation during the voltage sag measured by the μPMU device is used to calculate the sag source current. The terminal bus voltage variation is calculated by assuming that the voltage drop source is located at each bus node of each hierarchical circuit, and the voltage drop source is located according to the error between the calculated value and the measured value of the terminal bus voltage. In order to realize the fast and accurate positioning of voltage sag source, a binary search method is proposed to quickly and accurately locate the voltage sag source. The proposed algorithm is verified in Matlab. The results show that the proposed method has high positioning accuracy for different locations and different types of voltage sag sources in the distribution network.

Secondly, aiming at the problem that the calculation amount of voltage sag source location algorithm for large-scale distribution network is relatively large, a sag source location algorithm for complex radial distribution network based on distribution network partition equivalence is proposed. Firstly, the depth-first search algorithm is used to find the longest path of the distribution network and calculate the weight of the longest path node. Combined with the requirements of the distribution network partition, the distribution network is divided into multiple sub-partitions, and the equivalent impedance equivalent is adopted for the external circuits of each partition. On the basis of partition equivalence, it is assumed that the sag source is located at each bus node to calculate the terminal bus voltage error, and the partition and hierarchical circuit of the sag source near the bus are determined according to the error size. The binary search method is used to quickly and accurately locate the voltage sag source. By reducing the order of the impedance matrix and the number of buses contained in the hierarchical circuit, the efficiency of voltage sag source location is improved. Through the simulation verification of IEEE-33 node example, the sag source location algorithm of complex radial distribution network based on distribution network partition equivalence has the same positioning accuracy as the sag source location algorithm of simple radial distribution network, and the time required for positioning is significantly shortened.

Finally, the evaluation indexes of voltage sag severity on the grid side and the equipment side are established for a single voltage sag event. The weight function and the energy index function are used to evaluate the severity of voltage sag events from the equipment side and the grid side respectively. Aiming at the non-rectangular wave voltage sag, a voltage sag severity evaluation method based on curve fitting is proposed. The least square method is used to fit the non-rectangular wave voltage sag waveform, and the fitting function is used to evaluate the non-rectangular wave voltage sag, which improves the accuracy of the non-rectangular wave voltage sag severity evaluation. By evaluating the severity of the non-rectangular wave voltage sag waveform obtained by simulation, it is verified that the non-rectangular wave voltage sag severity evaluation method based on curve fitting is simple and efficient, easy to operate and implement in engineering, and has high engineering application value.

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