在碳达峰、碳中和目标的推动下，能源结构优化与可再生能源开发成为关键任务。分布式发电系统因具备环保与经济优势而发展迅猛，光伏、风电等分布式电源在电网中的接入规模持续扩大。然而，分布式电源（Distributed Generation，DG）的广泛应用对电力系统的稳定性和可靠性提出了新的挑战。当线路发生短路故障时，DG并网点的电压容易越限，进而导致DG脱网引发多级电压暂降，造成更大的电网安全问题。在此背景下，需要对考虑DG连锁脱网的配电网进行风险评估，这可以帮助识别和量化DG脱网后可能带来的各种风险，为电网的稳定运行提供有力保障。

首先，对DG连锁脱网下的多级电压暂降波形进行了分析和总结。以暂降幅值和持续时间为电压暂降的特征量，分析了DG加速脱网和不加速脱网的多级电压暂降波形。同时考虑了电网结构、继电保护类型以及故障位置对多级电压暂降波形的影响，并以PSCAD仿真软件设置不同场景进行波形仿真，所得结果与理论分析结果基本一致，为DG脱网概率评估和配电网风险评估提供了基础。

其次，提出基于低电压穿越不确定性的DG脱网概率评估方法。结合低电压穿越曲线（Low Voltage Ride Through Curve, LVRTC），考虑低电压穿越的不确定性，基于正态函数的分布规律刻画不确定区域的虚拟上下限曲线，由此构成DG低电压穿越的不确定性区域。用正态分布密度函数表征其脱网的随机特性，基于低电压穿越不确定性区域提出了DG脱网概率评估方法。在此基础上，采用经过多级电压暂降电压幅值等效计算后的幅值进行DG脱网概率评估，避免了欠评估。

最后，提出DG连锁脱网下的配电网风险评估方法。基于低压配电网的安全运行条件，建立了配电网风险评估指标。通过BWM法和CRITIC法分别确定各风险指标的主客观权重，引入组合赋权通过拉格朗日乘子法得到各风险指标的组合权重。从事故发生可能性和后果严重度两个方面，构建了基于DG连锁脱网的配电网风险评估方法。通过改造后的IEEE-30系统进行多场景仿真验证，结果表明本文提出的风险评估方法合理有效，为施加有效的风险防控和治理措施提供依据。

Driven by the goals of carbon peak and carbon neutrality, the optimization of energy structure and the development of renewable energy have become key tasks. Distributed generation systems have developed rapidly due to their environmental and economic advantages, and the scale of integration of distributed power sources such as photovoltaics and wind power into the power grid continues to expand. However, the widespread application of Distributed Generation (DG) poses new challenges to the stability and reliability of power systems. When a short circuit fault occurs in the power line, the voltage at the grid connection point of the distributed power source is prone to exceed the limit. It will cause DG off-grid and multi-stage voltage sag, resulting in greater power grid safety issues. In this context, it is necessary to conduct a risk assessment of the distribution network considering the cascading disconnection of distributed power sources. This can help identify and quantify various risks that may arise after DG off-grid, providing strong guarantees for the stable operation of the power grid.

Firstly, the multi-stage voltage sag waveform under the cascaded tripping-off of DG was analyzed and summarized. The multi-stage voltage sag waveforms of DG accelerated and non-accelerated disconnection were analyzed based on the characteristic quantities of voltage sag amplitude and duration. At the same time, the influence of power grid structure, relay protection type, and fault location on multi-level voltage sag waveform was considered, and different scenarios were set up using PSCAD simulation software for waveform simulation. The results obtained were basically consistent with theoretical analysis, providing a basis for DG off-grid probability assessment and distribution network risk assessment.

Secondly, a DG off-grid probability assessment method based on low voltage ride through uncertainty is proposed. Combined with the low voltage ride through curve ( LVRTC ), considering the uncertainty of low voltage ride through, distribution law of the normal function is used to describe the virtual upper and lower limits of the uncertain region, thus forming the uncertainty region of DG low voltage ride through. The normal distribution density function is used to characterize the random characteristics of the off-grid, and the DG off-grid probability assessment method is proposed based on the low voltage crossing uncertainty region. On this basis, the amplitude after the equivalent calculation of the multi-stage voltage sag voltage amplitude is used to evaluate the DG off-grid probability, which avoids the under-evaluation.

Finally, a risk assessment method for distribution networks considering the cascaded tripping-off of DG was proposed. Based on the safe operating conditions of low-voltage distribution networks, risk assessment indicators for distribution networks have been established. Determine the subjective and objective weights of each risk indicator using the BWM method and CRITIC method, and introduce combined weighting to obtain the combined weights of each risk indicator using the Lagrange multiplier method. A risk assessment method for distribution networks based on DG cascaded tripping-off was constructed from two aspects: the possibility of accident occurrence and the severity of consequences. Through multi scenario simulation verification using the IEEE-30 system, the results show that the risk assessment method proposed in this paper is reasonable and effective, providing a basis for implementing effective risk prevention and control measures.

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