Research On Economic Dispatch Of Power System Based On Quotient Space Granular Computing

With the development of human society,the demand for electric energy is increasing.The structure of power system is more and more complex with expanding scale.In order to improve the economic efficiency of the power grid and reduce the cost,at the same time,reducing the energy consumption and alleviating environmental pressure,it is of great significance to study the optimal operation of the power system.Economic dispatch has always been one of the most important subjects.Economic dispatch is a constrained optimization problem with high-dimension,non-convex and nonlinear characteristics.Therefore,it is very difficult to handle the problem,especially the coupling constraints.Granular computing is a methodology for solving complex problems.It simulates human's thinking mode to granulate the practical complex problems which will be solved from different levels and different granularity.Granular computing is widely used in the field of information technology.In this paper,the ideal of quotient space in granular computing is introduced to solve economic dispatch problem.The main work is as follows:Firstly,according to the theoretical characteristics of quotient space in granular computing,a stratified granulation method is promoted to build hierarchy quotient space model for economic dispatch problem so as to reduce the dimension of the problem and improve the computational efficiency of the algorithm.A new balance constraint processing method is proposed and combined with particle swarm optimization.The efficiency and accuracy of the proposed method in dealing with low dimensional economic dispatch problems are demonstrated through simulation analysis.Secondly,an economic dispatch model based on granular computing is established.On the basis of the principle of quotient space in granular computing,the equivalent granulation method for the unit is put forward according to the similarity degree of the incremental ratio of consumption,and the calculation formula of the equivalent parameters is derived.A single unit is regarded as fine granule,and the equivalent unit of multiple units is corresponded to coarse granule.The granularity is determined by the number of units contained in the granule.The calculation parameter of the granule is the equivalent parameter of the units it contained.The structure of the hierarchical quotient space is determined by granularity.An intelligent optimization algorithm is applied to implement calculation from top to bottom layer so as to obtain the final optimal results.Simulation results show that the stratified granulation method based on quotient space granular computing theory is effective for solving economic dispatch problem,which greatly reduces computation time.Finally,in order to reduce the time consumption of the power flow calculation in economic dispatch with line constrains,a power flow calculation method based on quotient space granular computing is proposed to stratify and granulate the topology of the power grid.Then,the network is simplified by Ward equivalent method retaining boundary nodes and PV nodes.The calculation progress is carried out in each granule as the executive element.The Newton-Raphson method is used to calculate the power flow from top to bottom layer.Simulation analysis is carried out on IEEE 39-bus and IEEE 118-bus system.The results demonstrate that the proposed granular computing approach is correct,effective,and can ensure the accuracy and efficiency of power flow calculation.