Reactive Power Impacts on LCL Filter Capacitor Lifetime and Reliability in DFIG Grid-Connected Inverter

With the increasing penetration of renewable power, its reliable and cost-effective production is of more and more importance. A filter is normally inserted between the grid-connected inverter and the power grid to reduce the PWM switching harmonics. According to an electro-thermal stress evaluation, the time-to-failure distribution of the single LCL filter capacitor is investigated in detail. Aiming at the system-level reliability analysis, a Weibull distribution based component-level individual capacitor can be linked together by using the reliability block diagram. A case study of a 2 MW wind power converter shows that the lifetime is significantly reduced from the individual capacitor to the capacitor bank. Besides, the over-excited reactive power injection further reduces the lifetime of the LCL filter capacitors.