Research On Modern Urban Power Grid Restoration Technology

In the near future,billions of urban residents' quality of life depends on the city to save energy,reduce pollution,improve living conditions,and ensure public security,etc.The energy infrastructure is arguably the single most feature in any city.If unavailable for a significant enough period of time,all city functions will eventually cease.With the development of social economy and the advancement of urbanization,as key component of the urban energy infrastructure,modern urban power grid is gradually showing characteristics of receiving-end power grid,shortage in power supply restoration capacity,enhancement in distributed energy penetration rate and network topology complexity,etc.For the features and development tendency of modern urban power grid,it's important and valuable to further research and establish suitable modern urban power grid restoration technology.Around the urban power grid restoration,this paper establishes the urban transmission(main)power grid fundamental restoration mechanism,the distribution power grid self-governing restoration strategy,and the urban transmission-distribution power grid coordinated restoration technology respectively.Besides,this paper also researches on the urban power grid restoration assessment method.The main contents of this paper are as follows:(1)For urban main power grid,the urban main power grid fundamental restoration mechanism is established.For the receiving-end urban power grid,unit with fast cut back(FCB)capacity and large scale battery energy storage system(BESS)are considered as main power grid's new start-up power sources.The modeling of main power grid's start-up power sources is improved and recovery time models of conventional thermal unit and transmission line/transformer branch are constructed.The urban main power grid fundamental restoration mechanism consists of bi-level optimal model.In the upper-lever,units' start order is optimized based on the units' start-up models in the main grid.In the lower-level,considering minimal restoration cost as the optimization goal,the restoration path and time-phased restored network are determined.Restoration scheme determined by the optimal model needs constraints check(e.g.operating time constraint and network power flow constraint etc.).Through iterations between upper and lower optimal levels,the entire urban main power grid restoration scheme can be determined.(2)For urban distribution power grid,the urban distribution power grid self-governing restoration strategy is established.After blackouts in the urban power grid,before the main grid restored,considering the application of distribution generations(DGs)like gas turbine unit,wind power generator,PV generator and energy storage in regional distribution power grid to restore partial network and maintain the power supply of some important load.The power balance of the restored partial network is maintained,and the partial restored regional distribution power grid is operated in self-governing mode.Models of DGs are established and improved.For intermittent type DGs(e.g.wind and PV),take usage of forecast technology and energy storage to alleviate the affection of the uncertainty and volatility to the distribution grid restoration.For constraints(e.g.radial topology constraint and network power flow constraint etc.),suitable constraint expression forms are considered to fulfill the solution of the distribution power grid self-governing restoration strategy optimal model in multi-time sections.(3)Based on the urban main power grid fundamental restoration mechanism and the distribution power grid self-governing restoration strategy,the urban transmissiondistribution power grid coordinated restoration technology is established.Considering the correlation of the main grid restoration and the distribution grid restoration,during the design of the coordinated restoration mechanism,the coordinated optimization of two optimization goals(i.e.system generation capability in main grid restoration and load restored and served in distribution grid restoration)is mainly focused.The main power grid restoration and distribution grid restoration are merged into a entire optimization problem.Based on the boundary nodes of the main grid and the distribution grids,the urban transmission-distribution integrated network model is constructed.The load level classification in urban power grid is refined and the optimization goals of both main grid and distribution grids are synthesized to determine the optimization goal of the transmission-distribution coordinated restoration model.Besides the constraints considered in the main grid fundamental restoration mechanism and the distribution grid self-governing restoration strategy,constraints in the coordinated restoration model are further improved and the entire urban transmission-distribution power grid coordinated restoration technology optimization model is established and validated.(4)The urban power grid restoration assessment method is researched and a novel cloud-data envelopment analysis(Cloud-DEA)scheme assessment method is proposed.The Cloud-DEA method can be applicable for assessment of urban power grid restoration schemes.The general flow of scheme assessment is introduced.Based on the cloud model,the qualitative index evaluation cloud system is established to realize the quantitative conversion of qualitative indices.By joint utilization of the CCR-DEA model and the LJK-DEA model,the Joint-DEA model is established.On the basis of the qualitative index evaluation cloud system and the Joint-DEA model,the main steps of the Cloud-DEA method are presented in detail.The qualitative index evaluation cloud system can effectively implement the quantitative conversion of qualitative indices.And the Joint-DEA model ensures the robustness of the Cloud-DEA scheme assessment method.