Estimation of Parasitic Resistance of Electrolytic Capacitorand Filter Inductor and Prediction of Input Filter InducedOscillations in a Switch-Mode Magnet Power Supply

In switch-mode power converters with large ratings, it is important to be able to predict the parasitic resistances associated withcircuit elements such as electrolytic capacitor and filter inductor in the initial converter design stage itself to avoid the cost and timeassociated with actual design, prototype fabrication, and testing of these components. Knowing the values of parasitic elements isalso important as they decide the possibility of closed-loop instability, besides affecting the other circuit parameters. In this paper,a way to estimate the equivalent series resistance of electrolytic capacitor and the winding resistance of filter inductor is proposedleading to their closed form expressions in terms of system parameters. Using these, procedure to predict the closed-loop instabilityinduced due to the input filter is exemplified with illustrative calculations.