On-line fault detection of aluminium electrolytic capacitors, in step-down DC-DC converters, using input current and output voltage ripple

The aim of this study is to present a simple on-line fault detection technique that is able to prevent structural failures in aluminium electrolytic capacitors used in the output filter of step-down DC-DC converters. The aluminium electrolytic capacitors equivalent circuit consists of an ideal resistance in series with an ideal capacitor and an ideal inductor. The first two elements change with frequency, temperature and aging. Most manufacturers define the end of life limit of these capacitors when their internal resistance (equivalent series resistance (ESR)) doubles or their capacitance (C) reduces by 20%, when compared with the initial values. The proposed on-line fault detection technique is able to estimate the capacitor ESR value during converter operation. For that purpose, a simple relationship between the input current and the output voltage ripple is used. The measurement system is composed of a digital oscilloscope that is connected to a microcomputer with 'Matlab' software. Several simulation and experimental results are presented to validate the proposed fault detection technique.