Output Impedance Modeling and High-Frequency Impedance Shaping Method for Distributed Bidirectional DC–DC Converters in DC Microgrids

Output impedance characteristics of interfaced converters of energy sources are the important indicators to assess the anti-interference ability of the dc microgrids. However, the output impedance is often approximately modeled by neglecting the impacts of delay units. In order to accurately study the anti-interference ability, the output impedance of an energy storage system is modeled with the consideration of the coupling characteristics of the current control gains and the delays caused by digital control and switching. The constraint mechanism of the coupling factors to impact the effective bandwidth of current loop in a load current feedforward system is also revealed. Then, an impedance shaping method is proposed to improve the anti-interference ability by optimally shaping the high-frequency output impedance, and also to improve system performances in terms of increasing the bandwidth of inner loop and the stable margin of outer loop. The simulation and experimental results both clearly validate the correctness and feasibility of the proposed impedance shaping method.