Mission Profile Based Reliability Evaluation of Capacitor Banks in Wind Power Converters

With the increasing penetration of wind power, reliable and cost-effective wind energy production is of more and more importance. The doubly-fed-induction-generator-based turbine system is widely used and dominates the wind market. In this paper, an analytical approach to assess reliability for power capacitors, both the dc-link capacitor bank and ac-side filter capacitor bank, is presented considering the annual mission profile. Based on the electrical behavior at various loading conditions, the lifecycle of the single power capacitor can be predicted through its electrothermal stresses. This percentile lifetime can be translated to the Weibull lifetime distribution of the power capacitor by considering the parameter uncertainties and tolerance variations. Thereafter, a reliability block diagram is used to bridge the reliability curves from the component-level of the individual capacitor to the system-level of the capacitor bank. A case study of a 2-MW wind turbine shows that the lifecycle is significantly reduced from the individual capacitor to the capacitor bank, where the dc-link capacitor bank dominates the lifetime consumption. Furthermore, the electrical stresses of the power capacitors are experimentally verified at a down-scaled 7.5 kW prototype.