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This paper introduces large-signal impedance for the modeling and analysis of sustained resonance in grid-connected converters. The large-signal impedance captures the converter impedance response for different amplitudes of the injected perturbation. Large-signal impedance based calculation of the sustained resonance amplitude (interharmonics) is presented for a grid-connected three-phase voltage source converter (VSC). The paper shows that hard nonlinearities, such as PWM saturation, dominate the sensitivity of the impedance response to the perturbation amplitude. The paper also presents modeling of the large-signal impedance for VSC; modeling challenges in the absence of the small-signal approximation and their solutions are discussed.
Shah et al. (Sat,) studied this question.