Input impedance modeling of digital controlled bi-directional DC/DC converter with inductor current feedback

To investigate the input impedance of digital-controlled bi-directional DC/DC converters, this paper develops a modeling method based on the sampled-data approach. Because the nonlinear pulse-width modulator generates sideband components, the sideband effect occurs in a closed-loop converter. And the sampling process of a digital controlled system can significantly influence the sideband components. Taking these effects into account, the simplified sampled-data model is proposed, which is applicable up to the switching frequency. In a current-mode-controlled buck converter, the introduced model predicts the loop gain is unchanged while alters the method of modulation (leading-edge, trailing-edge, etc.), while the conventional average model fails to explain this phenomenon. And the proposed model can suits the measured data of input impedance while there is a considerable gap at half of the switching frequency between the conventional model and the measured data. Simulation and experimental results are provided to verify the achievements of the proposed model.