This paper addresses the stability analysis of DC distribution networks with voltage source rectifiers (VSRs) and constant power loads (CPLs). Existing stability criteria for DC networks often rely on simplified models neglecting source converter controller dynamics, limiting their applicability in practical controller design. To overcome this, a singular perturbation-based framework is proposed to derive analytical stability conditions for closed-loop DC distribution network systems. By decomposing the high-dimensional Jacobian matrix into two structured low-dimensional matrices, tractable stability criteria are established using properties of Karush-Kuhn-Tucker (KKT) matrices. Sufficient stability conditions for local stability of a VSR-based DC distribution network are derived without requiring global VSR information, while a robust stability criterion dependent solely on maximum load data is developed to handle uncertainties. These results provide explicit design guidelines to enhance robustness and reduce computational complexity in stability analysis. Simulations validate the effectiveness of the proposed approach.

In this paper, we find that multiple attractors may coexist with the stable equilibrium point in an islanded microgrid containing identical grid-forming converters and a ring power network, which was once believed to be impossible in previous study. The existence of such an attractor separates the microgrid into several clusters, each of which is internally synchronized, but desynchronized with each other. We define a cluster coherence metric to measure the internal coherence of each cluster. Finally, full-circuit cycle-to-cycle simulation is provided for verification.

In conventional power systems dominated by synchronous generators, transient stability was found to be less influenced by the secondary control (e.g., automatic generation control). However, due to the flexibility of control and communication of grid-connected converters, more advanced control schemes such as the virtual-impedance-based distributed secondary control can be applied to multi-converter islanded microgrids, which may have a significant impact on the microgrid’s transient stability. In this paper, a simplified model considering the essential synchronization dynamics is established, and the metric named microgrid stable basin is proposed to measure the impact of critical secondary control parameters on the transient stability. Finally, laboratory measurement is provided to verify the theoretical findings.

Frequency damping control is a crucial aspect of islanded microgrids utilizing multiple virtual synchronous generators (VSGs). This paper studies the effects of line impedance mismatches and transient frequency out-of-sync leading to frequency interactive oscillation in VSGs. To address this issue, we propose a distributed interactive damping and zero-error control method that utilizes sparse communications. The objective of this method is to effectively suppress frequency oscillation by minimizing the differences in frequency dynamics among all VSGs. By implementing this approach, a low rate of change of frequency (RoCoF), accurate active power sharing, and zero frequency deviation are ensured. Through dynamic performance analysis, frequency characteristic analysis, and stability analysis based on LaSalle’s invariance principle, we demonstrate significant improvements in system stability, as well as dynamic and steady state performances. Finally, simulation and experimental results obtained under load changes, short-circuits, and communication faults validate the effectiveness of the proposed control method.