Review of protection systems for multi-terminal high voltage direct current grids.

Given the current evolution of Voltage Source Converters (VSC), Multi-Terminal High Voltage Direct Current (MTDC) grids are now becoming a real possibility. Still, some technical issues have to be addressed. The protection of High Voltage Direct Current (HVDC) grids is the main technical challenge that is slowing down the development of MTDC grids. Hence, this paper focuses on protection systems. Thus, protection devices, fault-clearing strategies and protection system requirements are considered. The main topic of this paper is the review of different types of protection methods for MTDC systems that are shown in the literature. They can be classified depending on the use of local measurements or a communication channel in their operation. The protection systems reviewed in this paper include protection systems based on current measurements, voltage measurement, traveling wave analysis and artificial intelligence. A protection system can employ only one of these methods or a combination of them. Finally, the main characteristics of the reviewed protection algorithms are compared, highlighting the system configuration, the converter technology, the adopted fault-clearing strategy, the implemented circuit breakers and the size of the limiting inductors. From the work presented in this paper, it is concluded that the actual tendency in MTDC protection systems is predominantly full-selective fault-clearing strategies combined with hybrid HVDC circuit breakers in series with limiting inductors. In addition, most protection methods are based on current measurement algorithms and a considerably high number of the reviewed protection systems employ a combination of several methods benefiting from their combined characteristics. • Review of protection systems for multi-terminal HVDC grids. • Classification into local-measurement-based and communication-based methods. • Current-based methods are more usually employed than voltage-based methods. • Combination of half-bridge MMCs and hybrid circuit breakers is predominant. • The preferred system configuration varies between symmetric-monopole and bipole. [ABSTRACT FROM AUTHOR]