Sammendrag
This paper presents a hybrid HVDC-transmission system composed by a Full-Bridge Modular Multilevel Converter (FB-MMC) and a Line-commutated Converter (LCC) from the grid integration of offshore wind farms. The operational characteristics of a three-terminal hybrid-HVDC system, e.i. two LCC stations plus one MMC station, are investigated using PSCAD/EMTDC. This paper mainly focuses on the performance of the system under ac faults at the LCC inverter. This condition is critical for the entire system because LCC is prone to commutation failure, which can be translated into dc faults on the hybrid system. Numerical results show that FB-MMC can help to alleviate ac faults conditions in the LCC, and the system is able to restart after clearance of the fault.