Using a sinosoidal PWM to estimate the ESR of Aluminum electrolytic capacitors

This paper presents a very simple technique that can be used to estimate the capacitors equivalent series resistance (ESR) at their operating conditions. Aluminum electrolytic capacitors are one of the most critical components in switch mode power supplies and in adjustable speed drives; yet, they are the preferred choice in those applications. The ESR changes considerably with frequency, temperature and ageing; besides the information given by manufactures is scarce. The knowledge of the ESR value is essential not only for designing purposes but also for evaluating the capacitors state condition. To implement the proposed technique, a buck converter is used together with a sinusoidal pulse width modulator to draw a sinusoidal current. The relationship between both capacitor current and voltage gives enough information to estimate capacitors equivalent circuit.