Characteristics Of The Fault Near Converter Station And Its Influence On Security And Stability Control Devices

With the rapid development of HVDC technology, there are more converter stations connect to the power system. However, when a fault occurs near the converter station, unique characteristics of electrical quantities will appear and it has very important research value. It is helpful for the improvement of the protection devices, security and stability control devices.In order to study the fault characteristics of converter station, a numerical model of fault calculation for AC-DC interconnected system under asymmetrical fault is studied. Two converter models that work effectively under asymmetrical fault are proposed. By simplifying the dynamic characteristics of the control system of HVDC, the numerical model of control system is proposed, and the circuit model of HVDC system is established. According the converter models, HVDC system is substituted as sequence impedance in the AC system or sequence power source in the AC system. Based on the models, symmetrical component method and iterative algorithm is used to solve the fault system. The calculation results in MATLAB and simulation results in PSCAD are compared under several fault conditions. It is proved that the proposed model and iterative calculation is accurate and effective for the asymmetrical fault calculation of interconnected system, and computational tools for fault characteristics study are provided.Simulation model that can reflect the actual AC-DC interconnected system and includes three HVDC line is built. Through the combination of simulation studies and theoretical calculations, fault characteristics are studied. It involves:Electric characteristic of the lines near the fault location, including AC side and DC side; Equivalent impedance characteristics of the HVDC system; Harmonic characteristics of the HVDC system; Controller features of HVDC system under fault condition. It is proposed that unique characteristic is exhibited from the converter station near fault zone. The fault characteristics are described in detailed and explained with theoretical calculations.Based on the summarizing of the fault criterion of security and stability control device, combining the fault characteristics of the AC-DC interconnected system, the applicability of the fault criterion is studied, the influence of the characteristic is proved.