A lifetime extension strategy for power devices in the wind power converters based on the distribution characteristics of consumed lifetime

The consumed lifetime due to the low frequency thermal cycling takes a great part in the total consumed lifetime of power devices in the wind power converters. Reducing the fluctuation of this thermal cycling can improve the reliability of power device significantly. However, since the maximum and minimum junction temperatures in each thermal cycle are determined by different wind speeds and ambient temperatures, it is difficult to determine the control target of this thermal cycling. To solve this problem, a lifetime extension strategy is proposed in this paper. The proposed scheme considers the minimum junction temperature fixed to the lowest ambient temperature and the allowed maximum junction temperature determined by the predefined fluctuation range. In this range, the thermal management is performed through switching frequency modification. The success of the proposed strategy lies in the selection of predefined fluctuation range so that the lifetime can be extended and the power quality can be guaranteed at the same time due to the manipulation of switching frequency for thermal management. Distribution characteristics of the consumed lifetime are employed to address this point. Performance of the presented strategy is verified through the case study of a 1.2 MW converter in the one year mission profiles. Results show that the total consumed lifetime of devices can be reduced by 76.16% in the grid side and 79.77% in the generator side. Moreover, the THD (total harmonic distortion) is guaranteed to be smaller than 4%.