Modeling for input impedance of buck converters and its application analysis

Impedance is very important for power electronic systems because of the close relationship between impedance and system stability. The power converters are typical nonlinear dynamic systems in frequency domain. With a sinusoidal input voltage perturbation excitation, the input current contains not only the input perturbation frequency, but also multiple other frequency components. Therefore, the input impedance has single input multiple output (SIMO) characteristic in frequency domain. However, traditional impedance modeling methods only take the component at input perturbation into consideration and simplify the model in a single input single output (SISO) form. They are actually simplifications of real input impedance in low frequency situation, which fail to explain some oscillations in distributed power system and micro-grid. This paper proposes a new input impedance model to describe its SIMO characteristic. The buck converter is introduced specifically as demonstration. The proposed model could accurately explain the oscillations in a system consist of two cascaded power electronic converters, whereas traditional models fail to do so. The simulation results validate the accuracy and effectiveness of the proposed model and obtained conclusions.