Power Flow Calculation And Optimization Of Power Network With Two-terminal HVDC Transmission Lines

In recent decades,China's economy has developed rapidly,but with it comes the negative impact of the depletion of fossil energy.In order to solve this contradiction,China began to vigorously develop new energy sources such as wind energy and nuclear energy.However,due to the limitation of distance,the transmission capacity of traditional AC transmission mode has been limited,so it is imperative to develop new transmission mode.Compared with AC transmission,HVDC transmission has many advantages,such as long distance,low cost and low loss.In recent years,HVDC transmission has been gradually integrated into China's distribution network.With the development trend of AC/DC hybrid power grid,it is necessary to study and analyze AC/DC system in terms of model building,power flow calculation and power flow optimization.At present,the research on AC system has been developed more mature,with a set of shaping theoretical system.Firstly,the commonly used algorithms for AC power flow calculation are introduced.Secondly,the transmission principle of HVDC transmission network added into hybrid network is analyzed,and then the qualitative principle analysis of AC/DC transition part-converter station and DC line is carried out.Then,the quantitative analysis of converter and DC line is carried out and their basic equations are deduced.In addition,this paper analyses the control characteristics of HVDC in detail,and gives several commonly used control methods.Based on the modeling of DC system,the power flow calculation of AC/DC hybrid system is carried out.The current power flow calculation of hybrid system includes unified iteration method and alternating iteration method.Because the convergence of the unified iteration method is good,this paper describes the solving process of the unified iteration method.According to the solving process,a MATLAB program is compiled to calculate the power flow of a specific example,and the results are compared with the simulation software to verify the effectiveness of the algorithm.After the validity of the algorithm is verified,the power flow calculation results under two different control modes are solved respectively.Under each control mode,the changes of DC line indices with AC voltage are observed,and the appropriate control mode is found.After obtaining the results of hybrid power flow,it is used as the basic data for power flow optimization,and the overall operating cost of the system is used as the objective function.The optimization algorithm uses modern interior point method,and compares the operation cost of the optimized system with that before optimization,which verifies the correctness of the algorithm.