A system and method for obtaining frequency-domain admittance/impedance using a few sets of time-series data. Utilizing an Eigensystem Realization Algorithm (ERA) or a dynamic mode decomposition (DMD), the input/output frequency-domain model reflecting voltage/current relationship is identified, and admittance/impedance identification is demonstrated for a grid-connected inverter-based resource (IBR) system. The proposed approach provides a powerful tool to replace the state-of-the-art harmonic injection methodology.We have developed an alternative method to characterize inverters through impedance by using only a few sets of time-series data. This data is then analyzed through Eigensystem Realization Algorithm (ERA) to find the frequency-domain models. In other words, step responses are used to find the dq-frame impedance or admittance models via ERA. The results show that the frequency responses of the impedances identified show a close match to the actual impedances measured. This technology can be useful for impedance-based stability analysis or in general where measured impedance plays a role in maintaining proper functions of machinery in the power industry.
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