  We consider a Th\'evenin equivalent circuit capturing the dynamics of a power
grid as seen from the point of common coupling with a power electronic
converter, and provide a solution to the problem of online identification of
the corresponding circuit parameters. For this purpose, we first derive a
linear regression model in the conventional abc coordinates and next design a
bounded observer-based composite identifier that requires local measurements
and knowledge of the grid frequency only. An extension that guarantees
exponential convergence of the estimates, under the additional assumption of
knowledge of the grid X/R ratio, is further provided. The performance of the
proposed identifier, which subsumes a conventional gradient descent algorithm,
is illustrated via detailed computer simulations.
