Research On Risk Assessment Method Of Flexible Distribution Networ

Under the background of accelerating global energy transformation,the connection of large amounts of renewable energy sources has brought challenges to the safe and stable operation of distribution system.Traditional distribution network is inadequate to cope with the uncertainty brought by wind or solar power generation.In contrast,flexible distribution network(FDN),which is formed by interconnecting multiple feeders through flexible power electronic devices,has the advantages of closed-loop power supply,controllable power flow,flexible access of distributed power sources and energy storage equipment,and has become a hot research topic at present.However,large amounts of renewable energy sources are connected to FDN,there are risks such as mutual coupling of AC risk and DC risk,and uncertainty caused by wind,solar,and load,which may lead to systematic failures and widespread power outages.In order to know the risk distribution and risk level of FDN,this paper studied the risk assessment method of FDN,and the specific contents are as follows:Firstly,the topology structure of FDN is introduced,and the working principle and control mode of Soft Open Point(SOP)are explained.A steady-state model of FDN with SOP is established,and an FDN model based on an alternating iterative method is established,the FDN power flow calculation method based on alternating iteration method is realized.Additionally,the definition,methods,index system,and basic process of power grid risk assessment are also introduced.Secondly,a risk assessment method of flexible distribution network based on a three-point estimation method is realized.FDN’s probability power flow calculation is achieved by combining a three-point estimation method with FDN’s power flow calculation based on an alternating iterative method,the probability density function of node voltage and branch active power is obtained by Gram-Charlier series expansion,the severity function is obtained using the utility theory preference function combined with the over-limit offset,and the FDN risk assessment is realized by establishing and calculating risk indicators according to the risk assessment theory.Taking three IEEE 33 networks interconnected by a three-port SOP as an example,the accuracy and high-efficiency of the risk assessment method are verified.Finally,a risk assessment method of flexible distribution network considering SOP optimization is proposed.In order to reflect the influence of SOP’s continuous regulation ability on FDN risk,a FDN risk assessment model that considers SOP optimization is established,particle swarm optimization algorithm combined with the FDN risk assessment method based on a three-point estimation method is used to solve the model,the obtained results are used to configure the SOP,and assess the risk of FDN.Taking three IEEE 33 networks interconnected by a three-port SOP as an example,it is shown that the proposed risk assessment method can reflect the influence of SOP’s continuous regulation ability on FDN risk;compared with the SOP control mode without optimization,the SOP control mode with optimization can give full play to the power flow regulation ability of SOP and make the risk of FDN lower.Then,Through the proposed risk assessment method,the FDN risk assessment of different access locations of SOP,different control strategies of SOP and multiple time periods is carried out.