An Economic Offline Technique for Estimating the Equivalent Circuit of Aluminum Electrolytic Capacitors

This paper presents an experimental technique that allows the determination of both reactance and equivalent series resistance (ESR) intrinsic values of aluminum electrolytic capacitors. The ESR is one of the most critical problems of static converters that operate near the resonance frequency of electrolytic capacitors. An increased ESR value leads to a significant increase in the alternate component of the output voltage, requiring constant action of the control system. In addition, manufacturers usually do not give the ESR value, but do give the maximum dissipation factor (DF), at the operating frequency of 120 Hz. From the DF, it is possible to determine the maximum ESR value at 120 Hz. Since the ESR value changes with frequency, and static converters operate at much higher ranges, designers need to compute its value at the operating frequency of these converters to reach the best design proposal. Moreover, almost all capacitor manufacturers give the capacitance value with a tolerance of 20%, whereas the proposed technique permits computation of its value with higher accuracy. Additionally, at low frequencies, if the ESR value of the capacitor is known, through its comparison with the maximum value given by the manufacturer, it is possible to estimate its condition. To validate the proposed technique and to demonstrate its applicability, some experimental results are presented and compared with the ones obtained with an impedance gain-phase analyzer and the manufacturers´ specifications for four different capacitors.