Modeling and analysis for output impedance of buck converters

In distributed power systems, the impedance model of power modules is very important because of the close relationship between impedance and stability. For buck converters with a sinusoidal current perturbation at the output terminal, the output voltage will contain multiple components in frequency domain. The output impedance characteristics of power converters are actually single input multiple output (SIMO). However, traditional models and modeling methods only take the perturbation frequency into account and ignore the other components. The obtained impedance models, with single input single output (SISO) forms, are actually simplifications of the real impedance. In this paper, the output impedance of buck converters with SIMO characteristics is modeled by a matrix based method. Detailed analysis shows that it is reasonable to only consider the perturbation frequency itself in low frequency regions, but in high frequency regions, especially those around the switching frequency and its multiples, the corresponding low frequency component is also very significant and should be taken into account. Simulation and experimental results validate the accuracy and effectiveness of the proposed modeling method and conclusions.