Power Flow Algorithms For Multi-terminal VSC-HVDC

The global fossil energy is faced with such problems as resource depletion and serious pollution.The new energy power generation such as photovoltaic,wind power proportion is increasing year by year,the randomness brought about as far away from the load center,generating new energy output and the system uncertainty problem is getting more and more attention.Compared with AC transmission technology,HVDC has a lot of technical and economic advantages in the new energy grid connection,and has developed rapidly in recent years.Compared with current source converter station,voltage source converter station has more flexible control and more stable operation characteristics,and is being popularized rapidly.When analyzing the transient and steady state operation,designing a more flexible control mode and studying the corresponding protection equipment,the network power flow calculation is the important premise and foundati on of its research.In this paper,the power flow calculation of HVDC system in multi voltage source converter station is studied,and the main contents are as follows.According to the basic principle and operation of VSC-HVDC,this paper summarizes the topology structure of double side and multi terminal VSC-HVDC system and its different control methods,a detailed analysis of its operating principle and SPWM control principle,and set up a steady and transient model of VSC-HVDC system,analyze the transient operation characteristics through MATLAB/Simulink simulation software.The VSC station as the inertia of the generator,studied the steady-state model of power angle characteristics of multi VSC-HVDC power flow based on Newton Raphson method and the construction of ideology,DC steady-state calculation of AC side based on Newton Raphson method,and verify the accuracy of the model by modifying the WSCC-9 node and IEEE57 node case.Based on the steady-state model of power angle characteristics of multi VSC-HVDC power flow in power electronic switching device model of equivalent uncertain problems,in this paper the steady-state model of loss characteristics of multiterminal AC-DC power flow based on VSC-HVDC.The VSC station is equivalent to a voltage station and a power station.The initial values of different equivalent models and other DC side power flow approximation models are derived.Voltage limit correction is introduced.Finally,the modified IEEE57 nodes verify that the new model is more accurate and converges faster.Study on the basic principle of droop control,deduced the two models mentioned in this paper is under the control of power flow calculation in the modified equation,analyze the deficiency in the strategy of modifying equations of multi terminal VSC-HVDC droop control system power angle based on the characteristics and modify ideas.The improved droop loss characteristics of multi terminal VSC-HVDC system control flow calculation model based on the proposed variable intercept DC voltage droop control and adaptive droop control flow equation modification strategy,through the IEEE57 node to verify the variable intercept DC voltage droop control has better voltage regulation ability and adaptive droop control system has faster recovery ability.