Research on the fault calculation of AC-DC interconnected system under asymmetrical fault conditions

A numerical model of fault calculation for AC-DC interconnected system under asymmetrical fault is proposed. It involves two converter models that work effectively under asymmetrical fault. Firstly the article establishes a converter model that based on switching function. In which HVDC system is substituted as sequence impedance in the AC system. The article proposes another converter model that based on the power factor of converter. In which HVDC system can be substituted as power source in the AC system. 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. Iterative algorithm is used to solve the fault system. The simulation results and calculation results are compared under several fault conditions, and the applicability of the model and switch function is discussed. Some further researches are carried out based on the numerical model.