Low-Frequency Input Impedance Models for Boost Single-Phase PFC Converters

Input impedance models of boost single-phase PFC converters suitable for predicting small-signal input characteristics below the line fundamental frequency are presented in this paper. Existing low-frequency input impedance models based on double averaging predicts input current responses to perturbations in the amplitude of the input voltage. It is shown that such impedance models don´t conform to the standard definition of impedances, hence cannot be used to study dynamic interactions between the PFC converter and the source in the conventional approach, in which the Nyquist stability criterion is applied to the ratio of the source output impedance to the converter input impedance. A new input impedance model that overcomes this limitation is then developed by using the method of harmonic balance. The new model conforms to the standard definition of impedances and predicts input current responses to superimposed input harmonic voltages. Numerical simulation and experimental results are presented for validation of the proposed model. Mathematical relationship between the two types of models are also presented to provide an alternative approach to the derivation of the new model