A comparison of WECS based on medium frequency AC-link for offshore DC Wind Park

In this paper a comparison of wind energy conversion system based on medium frequency AC-Link for offshore DC Wind Park is presented. The wind energy conversion system is based on three stages: an AC-AC converter, a medium frequency transformer and a full-bridge diode rectifier with DC output filter. Six converter topologies are compared for the AC-AC conversion stage. The conventional back-to-back converter, and modifications with squared wave output and with both single phase and three phase transformer, the direct matrix converter, the indirect matrix converter, and the reduced matrix converter are the selected topologies. Analytical models and numerical simulations are considered in order to evaluate the power losses, volume and mass as a function of the operational frequency of the transformer and the number of power converter sub-modules. The results show that wind energy conversion system based on direct matrix converter and back-to-back converter with squared wave output bring the best trade off between the efficiency, power density and power-to-mass ratio when the nominal power of 10 [MW] is considered.