Multi-terminal DC transmission system is an effective technology to achieve cross-regional interconnection of multiple energy and load centers

and it has strong competitiveness in both technical and economical aspects. In this paper

a overseas multi-terminal DC transmission project constructed by Chinese enterprises is taken as an example

the design and reactive power compensation of the AC filter for multi-terminal DC transmission project are studied. A converter station in this project is a weak AC system with high requirement to voltage stability. The nominal frequency of the converter station is 60 Hz. The IT product

the performance index of North American practice

is adopted in the design of the AC filter. In this paper

the difference between multi-terminal and double-terminal system as well as the hypothetical loop structure of IT product are introduced. On this basis

an AC filter meeting the performance requirements are designed and reactive power compensation is studied for the weak AC system of the the converter station. The research results in this paper have a certain reference for the final determination of the practical engineering AC filter scheme.