Comparative Analysis of the Large and Small Signal Responses of "AC inductor" and "DC inductor" Based Chargers

Abstract

Two approaches of operating inductors in switched mode power converters are compared. The classic method, utilized in most PWM converters, is to place the inductor in a path that has a non-zero average current. Such inductors are referred to here as "DC inductors". In contrast, inductors that operate with zero average current are denoted "AC inductors". The theoretical analysis carried out in this paper compares the small signal response of the current in the DC and AC inductors as a function of various system parameters, such as input and output voltages and duty cycle, in the case of the DC inductor, and frequency in the case of the AC inductor. The analysis was supported by large and small signal model developed in this study and verified against analytically derived large and small signal equations. The small signal current response was derived by applying average models. The analytical derivations and simulations of this study were verified experimentally. Good agreement was found between the theoretical predications and the analytical results. Based on the results of this study one can conclude that "AC inductor" based topologies are optimal for current sourcing applications, such as battery chargers, where differences between the average input and output voltages are expected to exist and develop over time.