A Service Restoration Method for Resilient Distribution Systems Considering Time-Varying Characteristic of Cold Load Pickup
Cai Sheng1, Xu Zhenqin1, Xie Yunyun1, Ding Bo2, Zhang Menglin3
1. School of Automation Nanjing University of Science and Technology Nanjing 210094 China; 2. State Grid Huai' an Power Supply Company Huai' an 223002 China; 3. School of Automation China University of Geosciences Wuhan 430074 China
Abstract：When an outage occurs in the distribution system due to extreme disaster events, the distributed generators are used to form microgrids and restore critical loads, which is essential for reducing outage duration and enhancing the resilience of distribution systems. The existing work utilizes the constant load model when designing the service restoration (SR) schemes. However, the ignorance of current unbalance caused by load peak when picking up cold loads may threaten the security of microgrids. Recently, SR approaches considering the cold load pickup (CLPU) were presented to ensure the supply-demand balance when restoring the distribution systems, but most of them simply assumed the system is three-phase balanced. This was insufficient to ensure a successful restoration because the violation of current unbalance factor may lead to the cut-off of distributed generators in microgrids. To address this issue, this paper proposed a SR method for three-phase unbalanced distribution systems considering the time-varying characteristic of CLPU. By restricting the current unbalance factor during the SR process, the security and reliability of microgrids can be improved. First, a time-dependent CLPU model was formulated when considering the relationship between CLPU characteristic and outage duration, and the sampling method was used to generate load demand profiles. Then, considering the constraints such as power balance constraint and current unbalance factor constraint, a SR model was formulated to maximize the amount of load restoration. Next, nonlinear constraints in the original model were linearized to facilitate the solution. The main differences between the proposed SR model and those in existing literature lie in the current unbalance factor constraints, by which the load pickup sequence at each phase is optimized to reduce the current unbalance of distributed generators. In addition, zone sectionalization, restoration paths, and load pickup sequences were jointly optimized to enhance the effectiveness of the microgrid-based SR scheme. Simulation results on the modified IEEE 37 node distribution system show that, after the event strikes, two microgrids are sequentially formed to restore the critical loads. Specifically, the black-start units are used to crank the non-black start units, and the line switches are closed orderly to extend the microgrids. The total generation of power sources in one MG is equal to the total amount of load consumption for each time step. The comparison with the SR method using constant load model shows that, the consideration of CLPU can improve the security of microgrid by restricting the current unbalance factor. The comparison with the SR method using traditional delayed exponential-based CLPU model shows that, the proposed time-dependent CLPU model can reduce the conservation of SR schemes. Comparison of different operation methods shows that, the utilization rate of the distributed generator for method with/without considering optimal microgrid topology is 100% and 85.5%, respectively. The following conclusions can be drawn from the simulation analysis: (1) Compared with traditional distribution system SR method, considering the CLPU characteristics can reduce the current unbalance factor, thereby enhancing the security and reliability of microgrids during the SR process. (2) The proposed model considers the relationship between CLPU characteristic and outage duration. Compared with the traditional CLPU model, a less conservative scheduling strategy can be obtained. (3) The proposed model jointly optimizes the network topology and restoration sequences. Therefore, more flexible MG topology can be obtained to satisfy the supply-and-demand balance and more critical loads can be supplied.
蔡胜, 徐振钦, 谢云云, 丁波, 仉梦林. 计及冷负荷启动时变特性的弹性配电网供电恢复[J]. 电工技术学报, 2025, 40(1): 139-151.
Cai Sheng, Xu Zhenqin, Xie Yunyun, Ding Bo, Zhang Menglin. A Service Restoration Method for Resilient Distribution Systems Considering Time-Varying Characteristic of Cold Load Pickup. Transactions of China Electrotechnical Society, 2025, 40(1): 139-151.
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2025, Vol. 40 
