DC Fault Analysis in MMC Based HVDC Systems along with Proposing a Modified MMC Protective Topology for Grid Stability

One of the most important issues in MMC based HVDC systems is lack of appropriate solution against DC fault. In this paper, firstly a summary of power transmission systems and their advantages and disadvantages are expressed. Then, types of HVDC system are investigated in detail. Structure types of HVDC is reviewed and its advantages over the conventional AC system are expressed. Then, the types of DC fault in the HVDC grid are examined. In section III, Modular Multilevel Converter (MMC) are expressed. Due to unique features of MMC, these converters have a higher acceptability than other topologies for use in a HVDC system. Since it is necessary to limit the fault currents to protect MMCs from serious short circuit faults against DC fault, several protection schemes have been introduced to deal with the DC short circuit faults. section V, analyzes such a new protective topology and operation principles to protect the MMC converter against DC short circuit fault. Finally, by simulating the HVDC grid short circuit fault, the protective performance of the proposed topology is investigated.