Research On Fault Line Selection And Location Method Of DC Distribution Network Based On VSC

In recent years,distributed power sources such as wind power and solar energy have developed rapidly,and the related technologies of flexible DC distribution networks have become hot research topics.The flexible DC distribution network is based on a Voltage Sourced Converters(VSC)system.After a DC system failure,the fault current rises rapidly,which is extremely harmful to the system safety,and is likely to cause the entire system to be shut down.It is immeasurable,so the research of fault location technology is the bottleneck restricting the development of DC distribution network.1.Analyze the basic structure,control strategy and grounding method of the voltage source converter station.The fault characteristics of the inter-pole short circuit fault and the single pole ground fault are studied,and the mathematical model of the fault characteristics in the three stages after the fault occurs is derived.2.A fault line selection method based on graph theory and a fault type identification method are proposed.After the fault of DC system,the fault current rises rapidly and there is no zero-crossing point.In order to solve the above problems,the faults caused by fault line selection and fault type identification are proposed.The fault line selection and fault type identification method based on graph theory is proposed.The whole distribution network is regarded as the “map” with the line convergence point as the apex and the connection line as the edge.The network topology matrix “D” is formed according to the current direction between the vertices,and the fault line is selected according to each element in the D array.At the same time,the di/dt fault feature quantity is extracted to further judge whether the fault occurs,and the misjudgment caused by the power flow reversal is avoided.To achieve fault type identification,a “double D method”is introduced.Finally,the effectiveness of the method is analyzed for faults of different types and different topologies.3.A fault location method based on genetic algorithm for DC distribution network is proposed.A mathematical model is established for the inter-pole short-circuit fault and the single-pole ground fault capacitor discharge phase in the DC line to eliminate the influence of the transition resistance and construct a fitness function.The fault location problem is transformed into a parameter identification problem.The appropriate fitness function is selected according to the fault type identification algorithm,and the problem is solved by the Genetic Algorithm(GA).4.The MATLAB/Simulink platform is used to build a six-terminal DC distribution network system based on AC main network,photovoltaic,energy storage,fan,AC load and DC load.The simulation results prove that the proposed fault type identification method is feasible and anti-interference ability.Strong.The proposed positioning methodhas strong resistance to transition resistance.The algorithm has high positioning accuracy,and it eliminates the interference of sampling information during sampling,and has strong robustness.