An Improved Impedance Estimation Method Based on Power Variations in Grid-Connected Inverters

This paper proposes an improved version of a grid-impedance estimation method based on imposed variations of active and reactive power injected by inverters into the grid. The variations cause changes in the synchronous voltage v_d and current i_q at the point of common coupling (PCC) between the inverter and the grid. These variations are used to calculate the grid impedance. The proposed improvement relies on a positive sequence estimator enhanced by a Fourier filter which provides harmonic rejection capability to the method. A complete evaluation of the proposed method is performed through simulations in Matlab/Simulink environment. The results show that the method notably refines the impedance computation in moderate weak grids.