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Real-Time Stability Analysis Based on Online Impedance Identification Method

With the connection of grid-connected inverters with various types and operating conditions to the grid, the problem of harmonic instability is prominent. It is of impedance to analyze harmonic stability, especially in a real-time way to return corresponding parameters timely. However, the operating points of grid-connected inverters are time-varying and the existing impedance measured methods cannot follow this change, which indeed hinders real-time stability analysis. Aiming at this gap, this paper presents an online impedance identification method, which enables real-time stability analysis. Firstly, multi-sinusoidal voltage perturbations are introduced to obtain the data needed in the subsequent steps. Then, the impedance of grid-connected inverter is identified online based on recursive least square algorithm. Finally, the generalized Nyquist criterion is used to perform real-time stability analysis based on the impedance identification results, and the correctness of theoretical analysis is further verified by simulation and experiment.