Control and analysis of a fault-tolerant offshore HVDC link fed by a bipolar DC collection network

Abstract

This paper presents a comprehensive investigation of a fault-tolerant bipolar HVDC link with electrodes utilized to interconnect an offshore wind farm. The wind farm’s generating units are interconnected in series through their dc terminals, which represents an emerging configuration for offshore wind farms. This novel approach allows achieving high transmission voltages without the need for a bulky offshore substation with transformers and rectifiers for direct current transmission. The proposed configuration involves the connection of two modular multilevel converters in a bipolar arrangement at the onshore substation. To evaluate its performance and robustness, extensive digital simulations were conducted using the PSCAD/EMTDC software. Various faults were applied to both the dc and ac terminals to demonstrate the flexibility and robustness of the studied topology. The results obtained from the simulations demonstrate exceptional capability of the bipolar HVDC system to maintain continuous operation, even in the event of a cable fault to the ground at the dc link. This research contributes valuable insights into the feasibility and advantages of employing a series-dc connection for offshore wind farms, offering a promising approach for future high-voltage transmission projects.