HVDC transmission for access to off-shore renewable energy: a review of technology and fault detection techniques

The ever-increasing demand for electric power has partially been met with access to offshore renewable energy, such as wind and tidal energy. With the development in power electronics, high-voltage direct current (HVDC) transmission is taking over as the primary choice for connecting off-shore generation to on-shore grids. Voltage source converter (VSC)-based HVDC is set to become the backbone of the multi-terminal DC grids replacing the conventional line commutated converter networks. VSC-HVDC networks offer the flexibility for HVDC grids to be connected as conventional AC grids in a meshed network. Advancement of technology has led to the development of the modular multilevel converter which has higher efficiency compared to the two-level VSC configurations. They are gradually becoming a popular choice. Although VSC-based grids offer a varied range of advantages, it is highly vulnerable to DC faults. Many designs of breakers have been patented over the years and various means have been proposed for their control. This study aims to review the available designs of HVDC terminals, the available protection devices and the protection and control methods for HVDC breakers. By comparing the state-of-the-art technologies that are currently available, this study aims to address the research issues and the additional research and development work that needs to be done.