Comparison of converter efficiency in large variable speed wind turbines

This paper presents a new and fast method for evaluating the efficiency of different power converter topologies in variable speed wind turbine applications. The method involves an accurate model of the considered generator while the converter models are based on ideal switches. The converter losses are modeled by analytical expressions of the switches, and the description of the losses incorporate both temperature, blocking voltage and switched current. The method is used to evaluate two converter topologies, a two-level back-to-back voltage source inverter (VSI), and a three-level back-to-back VSI for use in a 2 MW wind turbine system based on a doubly-fed induction generator (DFIG). From this evaluation, it appears that, with regards to the efficiency, the two-level VSI is the most suitable solution for the rotor side inverter while at the grid side, both inverter topologies show approximately the same efficiency. The evaluation method is validated by experimental results.