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Existing impedance-based stability criterion (IBSC) for electromagnetic stability assessment of multiple-grid-connected-inverter (GCI)-based power systems suffers from several limitations. First, global stability feature is hard to be obtained if Nyquist-criterion-based IBSC is used. Second, heavy computational burdens caused by either right-half-plane (RHP) poles calculation of impedance ratios or nodal admittance matrix construction can be involved. Third, it's not easy to locate the oscillation origin, since the dynamics of individual components are missing in the aggregated load and source sub-modules. This article aims to overcome the aforementioned three limitations of the existing IBSC. First, frequency responses of the load impedance and source admittance defined at each node in a selected components aggregation path are obtained by aggregating individual components (e.g., GCIs and transmission lines), from which imaginary parts of RHP poles of these load impedances and source admittances are directly identified without knowing analytical expressions of these load impedances and source admittances. Then, based on the Nyquist plots of minor loop gains (defined as the ratios of the impedance frequency responses of these load and source sub-modules), stability features of these selected nodes are obtained. Finally, if some nodes are unstable, the oscillation origin is located based on numbers of the RHP poles of these load impedances and source admittances. Compared to the existing IBSC, the presented method can assess global stability and locate oscillation origin more efficiently. The local circulating current issue, as a main obstacle of the existing IBSC, can also be identified. Time-domain simulation results in Matlab/Simulink platform and real-time verification results in OPAL-RT platform of a four-GCI-based radial power plant validate the effectiveness of the presented electromagnetic oscillation origin location method. |
