Interaction between EMI filter and power factor preregulators with averagecurrent control: Analysis and design considerations

The effects of a nonnegligible source impedance, due to the presence of an input EMI filter, on the stability of power factor preregulators (PFP's) wi th average current control are analyzed by using a state-space averaged mod el. Differently from previous approaches, it allows us to derive a simple e xpression for the loop gain in terms of the converter current loop gain. Th e overall system stability was studied for boost, Cuk, and SEPIC PFP topolo gies. Based on this model, a simple modification of the standard current co ntrol loop is proposed which increases the converter robustness against ins tabilities. Comparison between model forecasts and experimental measurement s was carried out using two prototypes, one based on the boost topology and the other based on the SEPIC topology, both rated at 600 W, Finally, the m odel accuracy was investigated with measurements at different current loop bandwidths.