This paper presents a novel finite control set Model Predictive Control (MPC) approach for grid-connected converters. The control performance of such converters may get affected from variations in the supply impedance, when its value is significant as compared to the converter line filter impedance. A novel idea for estimating the supply impedance variation, and hence the grid voltage, is presented in this paper. The estimation approach is based on the difference in grid voltage magnitude at two consecutive sampling instants. The grid voltage magnitudes are calculated on the basis of supply currents and converter voltages directly within the MPC algorithm, achieving a fast estimation and integration between the controller and the impedance estimator. The proposed approach has been verified using a 3-phase 2-level converter.