Thermal Analysis of Power Converters for DFIG-Based Wind Energy Conversion Systems during Voltage Sags

The doubly fed induction generator (DFIG) and back-to-back converter are very sensitive to power quality disturbances in grid-connected wind energy conversion systems (WECSs). Special attention has been given to protect the system from voltage sags, considering the introduction of several low-voltage ride-through (LVRT) techniques in the literature. However, only few works have really analyzed the behavior of power semiconductors during such phenomena in terms of the thermal stresses, whereas the existing studies are focused on balanced voltage sags only. In this context, this work presents a thermal profile analysis of power semiconductors in the grid-side converter (GSC) and rotor-side converter (RSC) considering a DFIG-based WECS submitted to symmetrical and asymmetrical voltage sags. The system is modeled using PLECS software and results on a 2.0 MW system are presented and thoroughly discussed. The results show that it is possible to meet the ride-through requirements during both balanced and unbalanced sags in terms of acceptable thermal stresses on the semiconductors as long as the back-to-back converter and its respective control system are properly designed.