In this paper, impedance modeling of a DC microgrid system consisting of a source and load converter, including an input filter, is performed. Impedance-based modeling has been used to derive mathematical models of the output impedance of the source converter and the input impedance of the load converter. The correlation between the converter interaction and system stability is analyzed based on the mathematical model. An impedance-based stability analysis is used to determine the system stability by analyzing the interactions among the converters in the DC microgrid system. Middlebrook’s stability criterion, which uses the impedance transfer function, is applied to determine system stability. Moreover, in this paper, a stability enhancement control algorithm is proposed to resolve the system instabilities resulting from interaction among the converters and the distortion caused by the harmonics emanating from the AC input. The proposed stability enhancement control algorithm consists of a feed-forward type virtual impedance (VI) and a proportional-resonant (PR) controller. The validity of the proposed method is demonstrated by the results of the response characteristics in the frequency domain, and the effectiveness of the proposed control algorithm is verified via simulations and prototype experimental models.

Sustainable energy, such as sunlight and wind energy, that comes from sources that do not need to be replenished has become important. Accordingly, the importance of the design and stable management of DC microgrids is also increasing. From this point of view, this paper analyzes the interaction between source and load converters constituting the DC microgrid using the derived mathematical input and output impedances models. This paper proposes a stability improvement method using the analyzed result. The method focuses on the presence or absence of input and output impedance overlap using Middlebrook’s stability criteria. To verify validity of the proposed method, a case study with three damping methods is conducted: (1) RC parallel damping with PR controller, (2) RL parallel damping with PR controller, and (3) RL series damping with PR controller. Additionally, the frequency domain characteristics and the Nyquist stability are analyzed using MATLAB, and simulation verification is conducted using PSIM. Through the analysis and simulation results, we confirm that the stability of the DC microgrid can be improved by applying the proposed method. The passive damping method analyzed in this paper is applied to an installed power converter, where it is possible to ensure the stability of the DC microgrid.