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.