Büttner, AnnaAnnaBüttnerWürfel, HansHansWürfelLiemann, SebastianSebastianLiemannSchiffer, JohannesJohannesSchifferHellman, FrankFrankHellman2025-08-042025-08-042025https://publica.fraunhofer.de/handle/publica/49012010.1109/TSG.2025.3591891The increasing integration of renewable energy sources (RESs) into power systems requires the deployment of grid-forming inverters to ensure a stable operation. Accurate modeling of these devices is necessary. In this paper, a system identification approach to obtain low-dimensional models of gridforming inverters is presented. The proposed approach is based on a Hammerstein-Wiener parametrization of the normal-form model. The normal-form is a gray-box model that utilizes complex frequency and phase to capture non-linear inverter dynamics. The model is validated on two well-known control strategies: droop-control and dispatchable virtual oscillators. Simulations and hardware-in-the-loop experiments demonstrate that the normalform accurately models inverter dynamics across various operating conditions. The approach shows great potential for enhancing the modeling of RES-dominated power systems, especially when component models are unavailable or computationally expensive.enInvertersGrid formingPower system dynamicsComputational modellingSystem identificationMathematical modelsPower system stabilityVoltage controlNonlinear dynamical systemsInvertersRenewable energy sourcesData-driven modelingjournal article