Abstract
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.
Highlights
Renewable energies, such as wind power and solar power, have been increasingly penetrating into the existing utility grid [1]
Avoidance of RHP poles calculation and location of oscillation origin commonly cannot be achieved in multiple-grid-connected inverters (GCIs)-based power plants by performing the Nyquist criterion (NC) one time at a selected node, since RHP poles may emerge during the components aggregation procedure, and the oscillation origin may be lost in the aggregated load and source sub-modules [16]–[18]
To fill in the research gaps mentioned in the above literature review, a computationally efficient global stability analysis and oscillation origin location method based on only terminal impedance frequency responses of individual components is presented in this article
Summary
The d-axis and q-axis grid current references. Proportional and integral gains of the current regulator. Norton equivalent circuit of the left part of node NK. Thevenin equivalent circuit of the right part of node NK. Thevenin equivalent circuit of the right part of PCC. The admittance and impedance frequency responses by seeing leftward and rightward at the right side of node NK. The admittance and impedance models by seeing leftward and rightward at the right side of node NK , and their frequency resposnes. Current source and admittance of the Norton equivalent circuit of GCI #K. Closed and open MLGs between SNrlK and SNriKght at node NK. Closed MLG between Z2p−1 and GCI #p at node Np
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