Abstract
Grid connected inverters are known to become unstable when the grid impedance is high. The impedance-based stability method requires only the inverter output impedance and the grid impedance to evaluate stability. Since it is a small-signal stability evaluation, the stability assessment is only valid for one operating point. This paper extends the impedance-based stability method to the stability evaluation of nonlinear and time-varying systems. For this purpose, in deviation from the classical approach, a separate investigation of the Norton and Thévenin equivalences under different operating points is carried out. Subsequently, by applying the generalized Nyquist criterion, a conclusion is derived about the stability for different operating points. The functionality of the proposed method was tested using an analytical model of the inverter and the grid, which was further confirmed by time-domain simulations.
Published Version
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