Variable AC transmission frequencies for offshore wind farm interconnection

Abstract

Non-standard AC transmission frequencies have been suggested in literature as a potential competitor to VSC-HVDC transmission for offshore wind farms integration (>100 km). Transmitting at lower than standard 50/60 Hz frequency provides the advantage of longer transmissible range for bulk AC power transfer and potentially lower losses in associated wind farm components. A higher than nominal frequency reduces the size of the required transformers and offshore platforms, potentially reducing cost substantially. This paper examines the selection of non-standard AC transmission frequencies from 1 to 100 Hz presenting a techno-economic analysis and methodology for comparing AC to standard benchmark VSC-HVDC technology in terms of power loss, size/volume of components, CAPEX and operation/maintenance metrics. It is shown at frequencies lower than 20 Hz, cost of energy is comparable to standard VSC-HVDC; due in part to lower number of cables required to carry full load power and the removal of the offshore VSC-HVDC converter station. The key contribution of this work is exploring the potential extended range of transmission capability for non-conventional AC frequency approaches that display comparable power loss and CAPEX/OPEX to VSC-HVDC based transmission for offshore wind integration.