Control and Stability of Modular DC Swarm Microgrids

Direct current (dc) microgrids have not yet achieved the promise of true plug-and-play characteristics due to stability issues stemming from power converters. Swarm microgrids, a type of dc microgrids, are aimed at delivering a modular and easy-to-expand infrastructure. In this article, an application-specific control strategy is developed to ensure stable and expandable swarm microgrids. This control strategy makes use of the widely available distributed storage in swarm microgrids and includes active damping techniques at power-drawing units. Utilizing a cascaded state-space system model, experimental validation with dual-active-bridge converters, and eigenvalue robustness analysis, this article demonstrates a high margin of stability for expandable swarm microgrids. The analysis includes variation of the microgrid size and line parameters, among others. The results show that swarm microgrids are stable for up to at least 1000 participating swarm units. As part of the robustness analysis of swarm microgrid stability, specific definitions are provided for the allowed behavior of the power converters used in a swarm microgrid. The developed methodology allows assessing and designing for swarm microgrid stability even without knowledge of the internal structures of the power converters. As such, this article provides a practical framework to support the scaling up of swarm microgrid deployment.