Research on output characteristics and control scheme of VSC during external short circuit fault

Inverter based electric power source constructed of semi-conductor switches is the most important part of DG, and its output characteristics is quite different from that of traditional generator power source during outward short circuit. Therefore, the operation and control of distribution grid will become very difficult if the proportion of inverter source is higher enough. A series of factors which affected the output current of the inverter power source during external short circuit are studied in this paper, after the structure and mechanism of the inverter and its controller is analyzed in detail. Three main factors, including the operation mode of the inverter, the parameters of the outer loop of the controller, and the type and parameters of the filter, are identified and studied with mechanism analysis and simulation verifying.