Thermal loading and reliability of 10 MW multilevel wind power converter at different wind roughness classes

This paper focuses on the design, thermal loading and reliability of a three-level Neutral Point Clamped (3-L NPC) back-to-back full scale converter for a 10 MW direct-drive wind turbine equipped with a Permanent Magnet Synchronous Generator (PMSG). The reliability performance of the three-level converter is strongly influenced by the thermal behaviour of the semiconductor devices and their mission profile which directly affects the lifetime and the cost of the whole converter. Therefore, the simulation platform is developed in Matlab/Simulink and PLECS simulation environment to analyse the dynamics of the system using different kinds of modulation strategies and analyzing different wind load conditions dependent on roughness classes. It is concluded that 60° discontinuous PWM modulation strategies show 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, also affecting the lifetime of the converter. Hence, the cycles lifetime largely decreases considering variable wind speed profile. In fact, the results show that the reliability of the converter is strongly affected by the temperature cycle behaviour and non-linear factors of the mission profile like turbulence, 3p effect and gust.