| With the deepening of the urbanization process and more widely using of the new energy access,the scale and complexity of the urban transmission grid is rising gradually.Especially,the blackout accidents occur frequently in recent years,the whole society is becoming pay more and more attention on transmission grid operation stability and power supply security.Therefore,ten years planning of ‘strong smart grid’ is presented by State Grid Corporation,which also illustrate that ensuring the strength of power grid should be superior to smart character and the foundation of the system set.So,how to build a strong city transmission grid to deal with the impact and challenge brought by the complicated and multi-source new system is worth studying and thinking.In the process of actual operation,transmission grid unavoidably suffered from the different types of disturbance from different sources,which results from natural birth defect existing in the network structure of city transmission grid itself and postnatal weakness caused by unreasonable system operation scheduling artificially.Existing urban transmission grid evaluation theory mainly falls into four categories: safety,economy,the network scale and the power quality of urban transmission grid to evaluate the rationality of the topology and operation.Although these mature index system can better reflect some characteristics of grid,but these index is much difficult to quantify the city power grid strength and internal supporting comprehensively in face of potential risks,which is not conductive to grasp the complex power grid overall.Meanwhile,compared with the traditional transmission grid,higher request is put forward in the transmission network expansion planning,blackout start,maintenance schedule and new energy access of city grid to make power transmission and asset utilization more reasonable,reliable and efficient.Therefore,on the analysis of the similarities and differences between the strength evaluation and the existing safety evaluation method of gird,putting forward in an urban transmission grid structure strong evaluation index system and method,and applying it in different research field like planning,operation and management of urban transmission network.Main research in the paper can be included as follow aspects:1.The strength of transmission grid structure is described systematically.Then,a clear distinction between structural strength analysis method with the existing transmission grid structure analysis method like security analysis method,vulnerability analysis method and anti-destroying ability analysis method is proposed.On the consideration of the mirco-marco characteristics of transmission network structure,a multidimensional structure strength evaluation index system is presented and index uniformity analysis evaluation method is introduced in the analysis process to replace absolute index by relative index for improving internal contact between each index,and avoiding the problem of dimension conversion between different indexes.2.Combined with hierarchical partitioning thought,regional power/load division method and the heterogeneity index of regional power/load distribution is put forward in the paper.The topological structure and running state index is used to evaluate the grid structure strength.Coefficient of Variance(C.V)of transmission load rate is defined as the quantitative index for analyzing the power flow distribution heterogeneity of transmission grid.On the basis of expansion costs and operation loss,the multi-objective transmission expansion planning optimization model with best structure strength respectively originated from regional internal transmission equipment and tie-line cluster between regions is established and solved.3.Based on the analysis and summary of traditional blackout partition recovery strategy,topology spectral clustering analysis with core node distribution uniformity in transmission grid structure strength index system is proposed;with limited fluctuation range of topology comprehensive index as topological constraints and the partition recovery time balance as the blackout partition benefit goal,the blackout partition recovery model with considering of the structure strength and subarea recovery time balance is proposed.Through the application of flexible time operator and the improvement of genetic algorithm,global optimization solution of the model is achieved.4.The characteristic of the potential cascading failure is expatiated and analyzed,and the risk indicator of the potential risk of cascading failure is defined.With the element quitting influence degree sensitivity analysis of the grid structure strength,its dependency from the whole network is defined.Under a certain confidence interval,taking system cascading failure risk sharing and the minimized maintenance cost as the goal,the grid maintenance optimization model with a variety of maintenance mode is proposed and solved.The importance of the key components to the grid structure strength and improvement of the overall system anti-interference ability from maintenance scheme optimizing under maintenance mode is inspected.5.Combining with the characteristics of electric vehicle charging and discharging,the advantage of centralized charging station compared with the traditional small charging station is illustrated.Combined with various daily load curves of electric vehicles,the daily areal battery swapping demand is determined.With the definition of grid time-sharing power supply moment index to describe the time-space characteristic of the city daily load flow,the power supply moment balance index and grid structure strength index are used to evaluate the transmission grid structure strength after the new energy access.On the basis of meeting battery swapping demand of electric vehicles in the area and considering the centralized charging station source-load switch arrangement during grid peak-valley load,locating and sizing optimization model of charging station to improve the overall grid structure strength is build and solved.Garver-6,IEEE-14,IEEE-30,IEEE-57,IEEE-128 testing systems and a real urban power network in East China are applied as examples to prove the validity of the models and analysis methods proposed in the paper. |
PDF Full Text Request