Locating And Sizing Of Partition Flexible Interconnection Device In Urban Power Grids

The urban power grid(UPG)is one of the city's major infrastructures.On one hand,large urban power grids,limited by the ever-increasing short-circuit current and electromagnetic ring,normally adopt partitioned operation mode;on the other hand,forced by environmental requirements and energy source problems,the feature of receiving power grid is increasingly noteworthy.The realization of partition flexible interconnection(PFI)is able to promote the security,stability and flexibility of urban power grids,where location and sizing of the partition flexible interconnection device(PFID)is a key question.In this paper,an integral locating and sizing method for PFID is proposed,which have been applied in the first 220 kV PFI pilot project.Firstly,the related concepts of PFI are presented.The flexible interconnection forms from two partitions to multi-partitions are analyzed.The scheme form of PFID based on back-to-back modular multilevel structure is clarified,including the structure of its sub-modules,main connection form at dc side and deployment of the link transformer.With the analysis of the operation features under different power grid conditions,three operation modes for PFID are proposed.Secondly,the locating method for PFID is presented,which consists of the initial selection stage and the optimal locating stage.In initial selection stage,unnecessary simulations for inappropriate location candidates can be avoided,so as to promote the computational efficiency;in optimal locating stage,the optimal location will be determined by comprehensively comparing five indices(including static security,transient voltage stability,power supply reliability,load balancing and total supply capacity)based on the analytic hierarchy process.Then,the maximum reactive power(or VAR)and capacity curve(MVCC)is obtained via deduction for the power operation range.Based on the sensitivity analysis,the methods to improve the output reactive power of the device are proposed.With the knowledge of MVCC,the sizing method for the device is presented according to the demand for active power support and reactive power compensation.Finally,the flow chart of locating and sizing method for PFID is depicted.And the proposed locating and sizing method is finally illustrated and validated on a practical power grid of Beijing(China)in 2017.