An Online Noninvasive Monitoring Technique for the ESR of an Output Capacitor in Switched-Mode Power Supplies

There are many types of switched-mode power supplies (SMPSs) with complex structures. The output filter of an SMPS often uses an electrolytic capacitor. When using these capacitors, it is very common that the capacitance decreases and the equivalent series resistance (ESR) increases. The present monitoring technique for the parameters of the output capacitor is mainly focused on a single topology form or multiple topology forms with similar characteristics, which depend on the main topology structure of the SMPSs. The applicability of a single topology type is not sufficient due to the presence of various types of converters. Also, the disassembling of the power electronic converters, or the removal of the capacitors for testing, may cause damage to the converters. To solve this problem, an online noninvasive monitoring technique for the ESR of the output capacitor in SMPSs has been proposed in the present study. This method only needs a parallel RC branch with a known resistance at the output end of the SMPSs during normal operation. Also, an equal white noise current should be applied to the output end of the SMPSs before and after the parallel RC branch. The ESR value is then obtained from the output white noise voltage signal and the resistance value of the parallel RC branch. The method is suitable for the output capacitor's ESR online monitoring of various ac-dc and dc-dc SMPSs topologies, which is not limited by the converter topologies. Also, this method functions irrespective of input signal, circuit structure, and main topology of the SMPSs. The effectiveness of the method has been verified by both theoretical simulations and experiments on different converters.