An overview of Fault Tolerant High Power DC-DC Converters for Application in DC Grid

Recently, there is rapid increase in the number of voltage source converter based HVDC transmission lines in order to couple the large offshore windfarms to the main ac power system. In comparison to the well-established point to point HVDC links, the multi-terminal HVDC grid is considered as the most efficient solution for high renewable energy penetration. It can provide many advantages such as secure power flow control, increased redundancy and higher efficiency. However, it still requires key enabling technologies such as dc-dc converter and dc circuit breaker for practical realization. Although, the dc-dc converter can provide many functionalities such as bi-directional power flow and dc voltage matching. However, the dc fault isolation in multi-terminal HVDC system has great importance. This paper firstly proposes a taxonomy of the most suitable converter topologies based on the structural affinities. Most prominent converters are classified into two major groups based on the internal isolation. Then, the basic structure, operating principle and performance capabilities of each converter is discussed in detail. Furthermore, the most promising dc-dc converter topologies are reviewed from the aspect of dc fault blocking capability and are compared in terms of cost effectiveness. Finally, we highlight prominent open research issues and provide few recommendations for the future research work.