Analysis and Design of Droop-Controlled Grid-Forming Inverters Using Novel WD Agg Approach

This article proposes the weighted dynamic aggregated (WD agg) model of large-scale systems consisting of \boldsymbol{n} grid-forming inverters in white-box islanded microgrids. The proposed WD agg approach models the microgrids \boldsymbol{n} grid-forming inverters, which have a similar control structure, by a single equivalent inverter and a controller that has a similar order and structure to the inverters in the microgrid. The parameters of the equivalent inverter and controller are obtained by considering the contribution of each state to the corresponding equivalent state. Compared with the existing models, while the complexity and computational burden of the studied system is reduced, the proposed WD agg model can provide an accurate single equivalent unit for a microgrid consists of a large number of grid-forming inverters with different sizes, operating points, and parameters. It is shown for various cases that the proposed WD agg model can be used in the steady-state, transient, and stability analyses with superior accuracy. The model can also be used to design the controller and inverters' parameters to ensure a desirable performance of the microgrid. The proposed WD agg model is evaluated by time-domain simulations and experimental implementation of four inverters connected to a load and CIGRE MV/LV benchmark for renewable energies for various case studies.