The increase of grid-connected converters has highlighted the problem of harmonic interaction between multiple converters and the grid. This phenomenon can bring to network instabilities. A valid approach in order to study the stability of the overall system is to characterize the converter with a smallsignal equivalent admittance model and stability analysis through the General Nyquist Criterion (GNC). This work analyses two different black-box methods to experimentally characterize the converter equivalent admittance model. The first method performs a voltage perturbation on grid side and evaluates the current response of the converter in order to estimate an equivalent transfer function, while the second method emulates a grid fault and evaluates the converter transient response.