Decomposition And Coordination Algorithm For Large Scale Optimal Power Flow Problems Under Voltage-grading And District-dividing

With the increasing demand of electric power,the scale of the power grid is expanding,and the interconnection of the regional power grids is advancing.The traditional centralized algorithm is more and more difficult to meet the requirements of real-time control and on-line analysis.Besides,there are many problem such as information leakage risk,data transmission bottleneck and "dimension disaster",etc.So a fast,efficient and stable decomposition and coordination algorithm has become the key to solve large-scale optimal power flow problems.In order to realize the decoupled calculation,a large power system is divided into several regional power systems by partitioning method firstly,then the decomposition and coordination algorithm is used to calculate multi-area optimal power flow.So this paper mainly involves two main contents,one is the partitioning method,and another is the decomposition and coordination algorithm of multi-area power system.Because 500kV/220kV electromagnetic loop network brings a lot of adverse effects to power system operation,so voltage-grading and district-dividing structure is the development trend of power grid.When open the 500kV/220kV electromagnetic loop network,the grid will become a voltage-grading and district-dividing structure.According to the characteristics,this paper propose a partitioning method based on 220kV voltage level.The large power grid is divided into 500kV and above voltage level main network and a number of 220kV and below voltage level regional networks.This method can not only get a few similar size and weakly coupled subnetworks,but also adapt to dispatching model based on voltage level.Node injection current method is used to divide the whole data into different regions.In order to solve the multi-area optimal power flow problem,two efficient decomposition and coordination algorithms are used,which are the decomposition coordination interior point method and the improved approximate Newton direction method.For decomposition coordination interior point method,the equivalent transformation of model is achieved by splitting the boundary nodes and adding the coupling constraints.Then use interior point method to solve the multi-area model,where each subnetwork can be optimized independently,only need to transfer coordination boundary variable information.This method can realize distributed computing.For improved approximate Newton direction algorithm,it is based on the approximate Newton direction algorithm,and the gradient of the power flow equation in the correction equation is preserved,so that the approximate Newton direction is closer to the complete Newton direction.The improved algorithm realizes the decoupling of the strong coupling system.Two kinds of decomposition and coordination algorithms have a common characteristic,that is their correction equation has a bordered block diagram form.The bordered block diagram form is very easy to be decoupled,so the dimension of the correction equation is decreased.The solution tends to be simpler and calculation speed is improved,and the purpose of distributed computation is achieved.Simulation results of ten voltage-grading and district-dividing grid systems are used to verify the effectiveness of the algorithms.Firstly,the node injection current method is used to realize the fast partition of the power grid,and then the two kinds of decomposition and coordination algorithms are used to calculate multi-area optimal power flow.The calculation results show that the two algorithms can improve the calculation efficiency and realize the decoupled calculation of large OPF.This decoupled calculation method also has wide application prospect for other large-scale optimization problems.