Analysis of Transfer Operation between Metallic and Ground Return Configurations for Multi-terminal HVDC Systems

This paper mainly focuses on the transfer operation between monopolar ground and metallic return configurations for multi-terminal high voltage direct current (HVDC) systems. For an HVDC system with more than two converters, there are several transfer sequences. How to choose a proper sequence seems to be a difficulty. To solve this problem, this paper takes an three-terminal HVDC system as an example. Different transfer sequences are discussed in details. The control method of transfer operation is also proposed to ensure the safe operation of the exemplified HVDC system. Numerical simulation studies with PSCAD/EMTDC are carried out to verify the theoretical results drawn by this paper.