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 (PFPs) with average current control are analyzed by using a state-space averaged model. Different from previous approaches, it allows us to derive a simple expression for the loop gain in terms of the converter current loop gain. The overall system stability was studied for boost, Cuk, and SEPIC PPP topologies. Based on this model, a simple modification of the standard current control loop is proposed which increases the converter robustness against instabilities. Comparison between model forecasts and experimental measurements 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 model accuracy was investigated with measurements at different current loop bandwidths