Analysis and Design of an Offshore Wind Farm Using a MV DC Grid

TLDR

This paper outlines the design of an offshore wind farm using a DC offshore grid based on resonant DC‑DC converters. The design employs multiphase resonant DC‑DC converters to step up voltage from individual generators to a MV DC bus and then to an HVDC line, and an aggregated model of parallel generators accurately approximates a detailed PSCAD model under varying wind conditions and transients. Compared to an equivalent AC‑grid wind farm, the DC‑grid design incurs slightly higher losses but markedly lighter magnetic components and cables; a fixed DC voltage offers marginally higher efficiency than a variable DC voltage, though the variable voltage reduces harmonics at the generator‑facing voltage‑source converter and the DC‑DC step‑up converter, and the aggregated model accurately reproduces a detailed PSCAD model under varying wind conditions and transients.

Abstract

This paper outlines the design of an offshore wind farm using a dc offshore grid based on resonant dc-dc converters. Multiphase resonant dc-dc converters are studied to step up the dc voltage from individual wind generators to a Medium Voltage (MV) dc bus, and from the MV bus to an HVDC line that will connect the wind farm to shore. Compared to an equivalent ac grid-based wind farm, a dc grid-based wind farm has slightly higher losses, but the weight of the magnetic components and cables is substantially lower. The analysis of operating permanent-magnet synchronous generators at variable and constant dc voltages shows that a fixed dc voltage has marginally higher efficiency than a variable dc voltage. However, using a variable dc voltage gives lower harmonics at the generator facing the voltage-source converter and the dc-dc step-up converter. An aggregated model of multiple parallel connected wind generators is developed and shown to accurately approximate a detailed PSCAD model during varying wind conditions and transients.