Analysis of Resonant Current Influence on Capacitor Lifetime Variation in LCL-Type Photovoltaic Systems

Ensuring reliability is vital for the efficient operation, maintenance, and cost-effectiveness of $LCL$-type photovoltaic (PV) inverters. The resonant currents triggered by the filter may transmit and couple between the grid and the PV system, thereby amplifying the electrothermal stresses on capacitors and resulting in notable inaccuracies in lifetime predictions. This article thoroughly analyzes capacitor lifetime to quantify estimation errors arising from resonant currents. Differing from conventional analysis, the electrical stresses with resonances are obtained by Fourier series and impedance characteristics of the $LCL$ filter. This method ensures that the model analysis remains independent of simulations, making it easy to modify and optimize. Furthermore, the capacitor's electrical stresses are validated experimentally. The findings indicate that resonant current significantly reduces capacitor lifetime. The damping method's failure leads to a 24% reduction in the capacitor bank's lifetime, with a notable 60% decrease observed particularly when utilizing a 15 $\mu$F individual capacitor. Ultimately, the comparison of average lifetime costs among various capacitor banks is conducted based on the proposed analytical model and reliability estimation method, aiming to optimize economic performance from a reliability perspective. The results of the lifetime investigation provide further insights into the $LCL$-type PV system design.