Short Circuit Fault Characteristics of Low Frequency AC Transmission System Based on Modular Multilevel Matrix Converter

Compared with power frequency AC transmission and DC transmission, low frequency AC transmission has its unique advantages, which is suitable for long distance transmission, large scale renewable generation and regulation of regional power grid. The fault characteristics affect the system design and operation, which is necessary to study. From the perspective of system topology and converter control, the characteristics of three-phase short circuit fault are analyzed and a simulation model is built on PSCAD for verification in this paper. After a fault occurs, it can be divided into two stages before and after the control responses. Before the control responses, the overvoltage is generated between the terminals of branch reactors and modular capacitors discharges. After the control responses, system characteristics are related to fault location and control strategy. The control and modulation of the converter can make the low frequency and power frequency systems interact with each other. This study can provide a reference for the parameters of equipment and converter control, as well as fault protection in low frequency systems.