Quantitative analysis of sustained oscillation associated with saturation non‐linearity in a grid‐connected voltage source converter

The interaction between the voltage source converter (VSC) and weak grid causes a negatively damped or diverging oscillation (DVO). generally evolves into sustained (STO) when governed by nonlinearities in VSC's control system, such as saturation of pulse width modulation (PWM). conventional small-signal impedance/admittance modelling (SSIM/SSAM) stability analysis methods are not suitable for characteristic STO. This paper presents large-signal model (LSIM/LSAM)-based quantitative method to better understand mechanism, characteristics, occurrence conditions LSAM extends SSAM incorporating nonlinearity PWM using describing function method. First, unique time-varying associated with is investigated. Then, two LSIM/LSAM-based criteria STO established based on an equivalent RLC circuit system. Three critical pieces information, including condition, frequency, magnitude, revealed criteria. Finally, LSAM-based applied investigate admittance VSC assess magnitude frequency Both results have been verified through time-domain simulations typical grid-connected VSC.