An Online Parameters Monitoring Method for Output Capacitor of Buck Converter Based on Large-Signal Load Transient Trajectory Analysis

Aluminum Electrolytic Capacitor (AEC) is one of the weakest components in power electronic converters. As the degradation of AEC happens, its equivalent series resistance (ESR) increases and the capacitance (C) decreases. Therefore, online monitoring of ESR and C to predict AEC’s life has great significance for ensuring safe and reliable operation of converters. In this paper, an online monitoring scheme is proposed for buck converters, aiming to estimate the ESR and C of AEC at the output side. The proposed scheme utilizes large-signal load transient trajectories to estimate the AEC parameters and has a relatively low sampling frequency. By analyzing the relationship between the transient trajectory and capacitor parameters, the ESR is directly calculated using the voltage and current step values at the initial instant of the transient. Further, C is calculated utilizing a calculation model derived from the output-voltage load transient trajectory. Corresponding simulation analysis and an online monitoring system implementation are provided. Furthermore, a 48V-12V buck converter with a digital PI controller and an analog V2 controller is built to verify the proposed online estimation method. The experimental results of the estimated ESR and C are consistent with the results measured by an LCR meter, and the estimation error is less than 10%.