| As an inherent attribute of power system,vulnerability can reflect the system’s ability to resist interference to a certain extent.The higher the system vulnerability is,the more sensitive it is to disturbances and the more likely it is to fail.The vulnerability of the system is mainly determined by the most vulnerable part of the system.Therefore,it is very important to identify the vulnerable parts of the system and to protect and monitor them for the safe and stable operation of the power system.Distributed generation(DG),as a supplement to traditional power grid,can reduce the burden of power grid and solve the problem of power consumption in remote areas.After DG is connected to the power grid,the structure and operation state of the power grid will change,thus affecting the vulnerability of the system.In order to ensure the safe and stable operation of the system,it is necessary to analyze the vulnerability of the system after DG access,understand the impact of DG on the system vulnerability,so as to rationally configure the DG according to the system vulnerability,so as to make the system more robust and stable.This paper is supported by “microgrid safety assessment and its multi-objective optimal control method research based on the vulnerability indexes”,subsidized by the National Foundation of China,No.51567019,evaluating the vulnerability of power system.Firstly,based on the existing vulnerability assessment indicators,this paper combines the power transmission efficiency indicators with the transmission capacity between generators and loads,and establishes the vulnerability assessment indicators of power system line structure.Then,according to the change of power flow of the remaining branches caused by line faults,the impact of power flow on the branches is divided into three categories.The residual power flow margin of the branches under each type of power flow impact is calculated,and the line power flow transfer entropy index is defined.At the same time,the system line operation vulnerability model is established based on line fault rate.Then the importance of the indicators is analyzed by analytic hierarchy process and entropy weight method,and the comprehensive vulnerability assessment indicators are obtained.The IEEE39 bus system is taken as an example to identify the fragile line,and compared with other literatures.The results show that the fragile line identification index in this paper is reasonable and effective.Several typical operation modes of DG are analyzed,which are divided into four types of nodes,and the corresponding grid-connected power flow calculation model is established.The power flow of DG-containing power grid is calculated by Niula method,and the vulnerability of the system is analyzed.The IEEE39 bus system with different access points,different power factors,different access capacities and different access quantities of PQ-node DGs is emphatically analyzed.By comparing the vulnerability of DG,it is found that some locations of DG access can improve the vulnerability of the system,and the improvement of DG access capacity on the vulnerability of the system is not linear,but there are extreme points.Based on the influence of DG on system vulnerability,a multi-objective optimization function considering system vulnerability and considering both active power loss and static voltage stability is established,and the configuration of DG is solved by quantum particle swarm optimization(QPSO).Optimize the whole network configuration for accessing single and multiple PQ nodes,and configure PQ nodes with constant power factor and variable power factor.Consider the actual installation of DG,optimize the regional configuration of DG,and configure a specified number of DG in the designated area to obtain the optimal access point and access capacity of DG under various conditions.Finally,optimize the single-objective and multi-objective.Configuration performance is compared and analyzed to prove the correctness and validity of multi-objective optimal allocation method. |
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