A Digital Twin Approach for Online Impedance-Based Stability Analysis of Three-Phase AC Systems

In contemporary electrical distribution systems, multiple parallel inverters collaborate to form an advanced power distribution network, which poses stability challenges. Small-signal analysis is a fundamental method for characterizing interactions between system impedances. In three-phase ac systems, stability assessment involves examining the source-to-load impedance ratio in the complex dq plane using the Generalized Nyquist criterion (GNC). In this context, the digital twin (DT) concept is arising as the forefront of energy sector digitization, providing real-time data through high-fidelity models mirroring physical systems. This article presents a stability analysis method employing a DT approach to determine the closed-loop impedance of the physical system and estimate the connected system's equivalent impedance. Broadband excitation based on pseudorandom binary sequences (PRBS) is applied with Fourier techniques for frequency response extraction. Impedance ratio assessment is performed on an edge-computing platform, delivering real-time stability information. Experimental results are provided for a dual-hybrid converter, one operating as a grid-forming system and the other in grid-following mode. The outcomes demonstrate the feasibility and potential of the proposal as a foundational approach to enhance robustness based on stability indexes.