Efficiency analysis of non-insulated converters for DC series collection in offshore wind farms

Collection schemes based on DC technologies appear as a possible alternative to present layouts of offshore wind farms to reduce the installation and operational costs. Within these internal DC collection schemes, series connection can be particularly attractive when a sufficiently high number of units are cascaded in order to reach a voltage level suitable for direct HVDC transmission. Power electronics assume an even more central role in these configurations and several converter topologies and related control strategies have been presented in literature. Within these topologies, non-insulated converters offer in general many advantages as a simpler structure and more standard components. Even though the conversion efficiency is a crucial aspect for an offshore wind farm, not enough comparative figures of efficiency for turbine units based on these converters have been presented. The paper presents a comparative efficiency analysis of a selection of non-insulated converter topologies for internal DC collection based on series connection.