Power Flow Calculation And Reactive Power Optimization Of AC/DC Hybrid System With VSC-HVDC

With the development of clean energy such as wind energy and solar energy,highvoltage direct current transmission(VSC-HVDC)based on voltage source converter has become the main transportation mode of electric energy.However,with the rapid development of VSC-HVDC,the power flow calculation and reactive power optimization of the traditional AC/DC hybrid system cannot meet the requirements.Under this background,this thesis mainly focuses on the shortcomings of the alternating iterative method in the power flow calculation of AC/DC hybrid systems with VSC-HVDC.An improved alternating iterative method based on dynamic convergence criterion is proposed,and then VSC-HVDC is established.The multi-objective dynamometer model of AC/DC hybrid system is compared with the AC reactive power optimization model to verify the superiority of the model.Based on this,the main contents of this paper are as follows:Firstly,by analyzing the advantages of voltage source converter(VSC),transmission mode and basic principle,the conclusion that VSC can realize flexible and independent control of active power and reactive power is obtained.The control mode of VSC-HVDC is established.The power flow calculation model of DC subsystem based on DC line and VSC is divided into common nodes and special nodes.The power flow calculation model of AC and DC hybrid system with VSC is established.Secondly,aiming at the shortcomings of the poor convergence of the alternating iterative method in the power flow calculation of AC/DC hybrid systems,an improved alternating iterative method based on dynamic convergence criterion is proposed.By analyzing the relationship between the convergence criterion and the maximum voltage error in the initial calculation of the power flow calculation,the improved method of convergence criterion is given,and the power flow calculation process of the alternating iterative method is improved.Through the simulation of the example,the convergence of the simultaneous solution method,the alternating iterative method and the improved alternating iteration method under different control modes are compared.The results show that the number of iterations of the improved alternating iterative method decreases and the calculation time is shortened.Finally,based on the power flow calculation with VSC-HVDC,a multi-objective optimization model with minimum voltage deviation and active power loss is established.By analyzing the relationship between the maximum power supply capacity of the system and the current load,the method for calculating the weights of active network loss and voltage deviation is proposed.The improved particle swarm optimization algorithm is used to solve the model,and the simulation analysis of the IEEE30 labeled node with DC is carried out.The results show that the reactive power optimization of the AC/DC hybrid system with VSC is better than the reactive power optimization of the traditional AC system,and the optimization of the network loss and voltage deviation is better,and the reactive power of the reactive power compensation device can be saved.