This paper focuses on the design, thermal loading, and reliability of a three-level neutral-point-clamped back-to-back full-scale converter for a 10-MW direct-drive wind turbine equipped with a permanent-magnet synchronous generator. The reliability performance of the three-level converter is strongly influenced by the thermal behavior of the semiconductor devices and their mission profile which directly affects the lifetime and the cost of the entire converter. Therefore, a simulation platform is developed in a Matlab/Simulink and PLECS simulation environment to analyze the dynamics of the system using different kinds of modulation strategies and analyzing the different wind-load conditions that are dependent on roughness classes. This paper shows that the 60 ° discontinuous pulsewidth-modulation strategies allow better thermal performance and increase the estimated lifetime of the converter. Furthermore, the increment of the wind roughness class causes a larger dispersion of the mean values and the variation of the junction temperatures, which also affect the lifetime of the converter. Hence, the cycle lifetime largely decreases considering the variable-wind-speed profile. In fact, the results show that the reliability of the converter is strongly affected by the temperature-cycle behavior and nonlinear factors of the mission profile such as turbulence, 3p effect, and gust.
Ieee Transactions on Industry Applications, 2014, Vol 50, Issue 1, p. 484-494