Grid-connected converters, when subject to grid fault conditions, should stay connected and support the network voltage via reactive power injection. The fulfilment of this requirement strongly depends on the dynamics and stability of the converter control system. It can be shown that local static instability, and the consequent local dynamic instability can be avoided if the grid impedance during the fault is known. This paper proposes a novel method to identify the grid impedance during the fault by using the grid fault disturbance as an identification pulse. The proposed identification method is implemented in a proof-of-concept detailed simulation model, and verified with experimental results.