Comparative Analysis of Alternatives for Virtual Impedance Representation in a Small-Signal Reduced-Order Model for Low-Voltage Islanded AC Microgrids

The development of high-fidelity and computational-effective microgrid models is crucial to assess the performance of microgrids in real-time applications. Therefore, the development of accurate reduced-order (R-O) microgrid models plays a fundamental role in the deployment of this concept. On the other hand, the virtual impedance techniques are essential for power decoupling and microgrid damping. However, the virtual impedance representation in R-O models has not been properly addressed in the literature. Hence, this paper explores two different alternatives for the virtual impedance representation in a reduced-order (R-O) microgrid model: i. the inclusion of virtual impedance inside the network model using Kron reduction; and ii. The inclusion of virtual impedance inside the grid-forming converter model. It was found that for low values of the voltage droop coefficient, both approaches provide similar results. However, as the voltage droop coefficient increases, the second alternative leads to more accurate results. Simulation and experimental results are presented in order to validate the analysis done.