Study On The Continuation Method And Its Application Based On Improved Step-Size Controlling And Parameterization

The safe and efficient operation of the power grid is essential for modern human society.When planning,designing and adjusting the power grids,it is necessary to conduct sufficient analysis and research on them,so as to make them as economical and efficient as possible on the basis of safety and reliability.Power flow calculation is the basic method to study the state of power grid,and it is indispensable to analyze the voltage stability of power grid.However,power flow calculations often fail due to the nonlinearity of the power flow equation.In order to solve this problem,according to the idea of continuation,the continuous power flow(CPF)is introduced.The essence of CPF is to introduce a parameter and form an extended equation,so as to solve the problem of Jacobian matrix singularity.CPF has become the most common static analysis method of voltage stability.But the traditional CPF also has the risk of calculating divergence,and its calculation takes a long time,especially not suitable for current large-scale complex grid system.So,it is necessary to improve it effectively.This paper does a lot of research on how to improve CPF,and applies the improved CPF to the calculation and analysis of an actual power grid.The specific contents are as follows.(1)The research status of continuation method is summarized.The model and classification of CPF are summarized systematically,and then calculation principle of CPF is introduced.As to four steps it contains,that is,prediction,step control,parameterization and correction,this paper describes and summarizes the specific methods of them.The reasons for the failure of CPF calculation are analyzed.Based on this analysis,this paper presents the idea of adjusting the step size and improving the parameterization method.(2)Proposing an adaptive step control method.Applying mathematical deduction,it is theoretically proved that the adaptive step-size method is more suitable for the sensitivity of PV curve than the two classical variable step-size methods.This method can make the step size change with the slope of the curve,thus greatly improving the calculation speed.The simulation results based on IEEE 39 bus system verify the rapidity of the adaptive step-size method.And with the increase of computing scale,the advantages of computing speed become more and more obvious.(3)Proposing a combined parameterization method.Taking the distance between the predicted point and the precise solution of CPF as the criterion to judge the quality of the parameterization method,this paper analyzes the performance of each parameterization method and finds that the different parameterization methods show different advantages and disadvantages in different CPF solution curve regions.Therefore,in order to fully exploit,utilize and complement the information of each parameterization method,a combined parameterization method is proposed,in which different parameterization methods are used in different regions of the PV curve.In addition,switching breakpoints of the combination parameterization method are set during the process of tracing PV curve,and the divergence of correction is used as the combination switching criterion.Based on the IEEE 39 bus,the simulation calculations are carried out in the case of fixed step size,classical variable step-size and adaptive step-size method,which verifies the effectiveness of the two improvements made in this paper.(4)Applying the improved CPF to a practical power grid.According to the installation,load and operation characteristics of the power grid,CPF calculation is carried out for one of the districts.From the obtained lambda V curve,the vulnerable area of the power grid in this area is obtained,and the power margin of the actual power grid is analyzed.Through the calculation and analysis of CPF,the result can provide data support for the planning and operation of the area,which reflects the engineering value of studying CPF.