Analysis of EMI filter induced instabilities in boost power factor preregulators

The effects of a nonnegligible source impedance, due to the presence of an input EMI filter, on the stability of boost power factor preregulators (PFP) are analyzed by using a simple state-space averaged model. Differently from previous approach, it allows to derive a simple expression for the loop gain in terms of the power converter current loop gain. Based on this model, a simple modification of the standard power converter current control loop is proposed which improves the power converter robustness. In order to assess the validity of the proposed approach, comparison between model predictions and experimental measurements were done using a boost PFP prototype rated at 600 W.