Research On Models And Computational Methods For Total Supply Capability Of Urban 220kV Power Grid

The operation complexity of city power grid is increasing day by day when the power grid expands due to the growth of electricity loads.With the development of 500 kV power grid,the role of 220 kV power grid which serves as the main grid of most cities is changing from transmission grid to distribution grid.Total supplying capability(TSC)of the 220 kV power grid is of great significance in revealing the safety margin of real-time operation and promoting the forward-looking planning of future grid,but there is no effective method to evaluate the TSC so far.Presently,repeat power flow simulation is still the most common way in static security checking in both power grid planning and operation.Firstly,the concept of TSC of 220 kV city power grid is proposed in this paper,following the comprehensive analysis of the topology structure and connection forms of 220 kV city power grid.According to the common characteristics of the topology and operation mode of district-dividing,an idea of decoupling each district 220 kV power grid from the whole complete multi-levels power grid model is presented.After certain simplification of higher 500 kV and lower 110 kV power grid,a non-linear optimization model based on AC power flow and precise consideration of N-1 static security constraints is established for TSC evaluation of district 220 kV power grid.In order to tackle the “curse of dimensionality” caused by a huge number of N-1 security constraints,the basic frame of Benders decomposition method is adopted in this paper to develop a highly efficient algorithm for the proposed TSC-OPF model.According to the Benders decomposition frame,one master problem corresponding to the N state and several slave problems corresponding to those N-1 states are formulated separately to lower the dimensionality of the original TSC-OPF model.Then,to overcome the shortcomings of traditional serial/parallel schemes of the Benders decomposition method,an improved hybrid scheme including a fast contingency filtering technique is proposed in this paper to enhance both the performance and efficiency.Additionally,this paper illustrated the phenomenon of the out-of-balance load distribution in the pursuit of a single objective maximizing the TSC through a series of simulation studies.To redress this problem,this paper proposed a multi-objective optimization model considering both the TSC and the load balance,in which the load balance degree is measured base on the recommended load rate.The fast non-dominated sorting genetic algorithm(NSGA-II)is adopted to search the Pareto front,and an ideal degree sorting method based on entropy weight theories is used for decision making of the eclectic optimal solution.These models and methods can help to reveal the TSC of 220 kV power grid under balanced load distribution,and provide useful reference for unlocking the maximum supplying potential of power grid under the precondition of safety and reliability in operation.