Resonant Current Impacts on the Lifetime of LCL Filter in PV Systems

LCL filters are critical in PV inverter systems, and its resonant currents brings more electrothermal stresses on filter capacitors. This paper investigates the influence of resonant currents on damage of capacitors. Different from conventional methods, this paper predicts the lifetime of individual capacitors by comparing the dynamic hot spot temperatures with and without the damping method and using annual mission profiles. Then, based on Monte Carlo simulations and Weibull analysis, reliability curves are connected from the component level of the individual capacitor to the system level of the capacitor bank with help from the reliability block diagrams. The results show that without damping method, the resonant currents have a significant impact on capacitor lifetime. In the case that electrothermal stress concentrates on an individual capacitor, its lifetime is shorter than that of a capacitor bank. Furthermore, the average lifetime costs of different capacitor bank configurations are compared to provide a reference for capacitor selection.