Interaction between EMI filter and power factor preregulators with average current 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 with average current control are analyzed by using a state space averaged model. The modeling allows to derive a simple expression for the loop gain in terms of the converter current loop gain. The overall system stability is studied for boost, Cuk and SEPIC PFP topologies. Based on this model, a simple modification of the standard current control loop is proposed which increases the converter robustness. Comparison between model forecasts and experimental measurements is 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 model accuracy is investigated with measurements at different current loop bandwidths