Energy Storage Planning Method For Improving Security And Stability Of Multi-infeed Receiving-end System

China’s power demand in high load density areas is met by several large-capacity HVDC links centralized feed,but a typical receiving-end system is formed.The electrical connection between each HVDC links in the receiving-end system is close.The single AC system fault may cause simultaneous commutation failure,continuous commutation failure or even blocking of some HVDC links.which will cause serious impact on the power grid.In addition,large-capacity HVDC reduces the inertia level of the power grid and increases the risk of large-scale active power loss,fr-equency security is also facing challenge.Electrochemical energy storage has the characteristics of strong dynamic active and reactive power regulation ability,rapid response and flexible control mode.It is a high-quality resource to improve the safety of receivingend system.Therefore,it is necessary to carry out research on the planning method of energy storage in receiving-end system.The main work of this paper is as follows:(1)According to the different control modes of power conversion system(PCS),energy storage is divided into two types:grid-following(GFL)and grid-forming(GFM).When providing reactive power support,GFL is regarded as current source,GFM is regarded as voltage source.Then,the mechanism of improving the voltage security of the receiving-end system is analyzed,and the safety index considering the energy storage is constructed.In terms of frequency security,an energy storage and HVDC emergency active power support strategy based on system frequency response(SFR)model is designed.On this basis,a frequency security constraint model is constructed from two aspects:rate of change of frequency(RoCoF)and frequency lowest point.A double-infeed AC/DC system model is built in PSCAD/EMTDC to verify the proposed control strategy.(2)Taking the multi-infeed interaction factor(MIIF)and economic cost as the objective function,a two-layer multi-objective energy storage optimization configuration model is constructed to improve the voltage and frequency security of the receiving-end system.The upper layer is a multi-objective energy storage power station siting and sizing model.The lower layer is a daily optimal scheduling model,which is embedded constraint of RoCoF and frequency lowest point.And a solution process combining non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ)and solver is designed.Finally,an improved IEEE-39 system is used to verify the eff-ectiveness of the energy storage planning scheme from three aspects:voltage security,frequency security and operation economy.(3)Aiming at the strong nonlinearity of multi-infeed short circuit ratio(MISCR)with variables,the method of "accompanying network+model reconstruction" is proposed to realize the linearization calculation of MISCR,and the accuracy of the calculation method is verified.On this basis,considering the differences in the mechanism and economic cost of GRL and GFM,the optimal configuration model of energy storage considering PCS selection is established.The idea of integrated modeling and solving of energy storage planning layer,system operation layer and accompanying network layer is adopted.Finally,the superiority of two types of energy storage coordinated configuration scheme is verified by simulation.