Multi-objective Design of a Modular Power Converter based on Medium Frequency AC-link for Offshore DC Wind Park

The design of a modular power converter based on medium frequency AC-Link for offshore wind turbines regarding efficiency, power density and power to mass ratio is described in this paper. The impact of four design parameters in the three objectives is studied. Such parameters are the AC-AC converter topology, the number of modules, and the number of phases and frequency of the AC-link. Six topologies are investigated and compared. The conventional back-to-back (B2B) converter, the B2B with three phase squared wave output, the B2B with single phase squared wave output, the direct matrix converter, the indirect matrix converter, and the reduced matrix converter are the selected topologies. The Pareto surface of the three objectives is obtained for a set of design parameters. It has been found that a wind energy conversion system based on a medium frequency AC-link will lead the best trade-off between efficiency, power density and power to mass ratio when the AC-AC converter topology is the direct matrix converter, the AC-link frequency is selected around 1 kHz and the power per module is in the range of 2.5 to 4 MW.