Análise comparativa dos métodos de estimativas das perdas em capacitores de barramento CC em inversores fotovoltaicos

Abstract

Inverters play a significant role in photovoltaic systems. Compared to other system elements, the inverter exhibits lower reliability due to its complex multifunctional nature. Electrolytic capacitors on the direct current (DC) bus are the components most likely to fail in photovoltaic inverters. Capacitor stress mainly occurs due to high average temperatures, making accurate estimation of capacitor power losses a crucial step in component thermal analysis. In this context, the present paper conducts a comparative evaluation of four methods for estimating capacitor losses, focusing on thermal response. The first method is performed considering a constant Equivalent Series Resistance (ESR), while the second and third methods consider the influence of operating frequency and capacitor temperature, respectively, on the ESR. The fourth method, in turn, combines the second and third methods, considering the influence of both frequency and temperature on the capacitor ESR. An approach using Lookup Tables (LUT) was implemented to mitigate computational effort, evaluating daily and annual mission profiles. The study results show the highest average temperature difference of 5.31%, between the methods with constant ESR and with ESR dependent on capacitor frequency and temperature.