Admittance Modeling and Stability Analysis for Inverter-Based Microgrid With Voltage-Source-Rectifier Load

Instability and low-frequency oscillation phenomenon of inverter-based microgrid (IBM) with voltage-source-rectifier load have obtained increasing concern. However, the influence of instantaneous angle of operation point on IBM is usually neglected during voltage faults, and it may generate the uncertain impact of voltage faults on the stable and safe operation of IBM. Besides, the influence of instantaneous angle of operation point may cause varying degrees of system oscillation and stability at a different angle of system states' change, including fault recovery. To solve this issue, a systematic approach of small-signal admittance modeling for IBM in the αβ frame is proposed in this article. The small-signal admittance model of each submodule (SM) of IBM is established and formed as a multi-input-multi-output (MIMO) system considering the actual closed-loop controls and decoupled strategies in the dq frame. Based on the proposed admittance models of SMs, the complete model of IBM is integrated and linearized, and the influence of both amplitude and instantaneous angle of operation point on the IBM stability is analyzed in small-signal model comprehensively. Besides, using the generalized Nyquist stability criterion (GNC), the influence of instantaneous angle in large-signal operation point on oscillation amplitude and stability of IBM is investigated. The proposed analysis approach can analyze and determine the responded oscillation and stability of the system more accurately during system states' variation, such as voltage sag and sudden changes in load. It also reduces the uncertainty of IBM behaviors during states' variation to ensure that IBM operates smoothly, flexibly, and stably. Finally, experimental results are presented to validate the correctness of the proposed analysis method.