Harmonics Frequencies Impedance Estimation Based on Least-square method

This paper presents an approach to estimate the grid impedance at fundamental as well as harmonics frequencies. The required measurements are voltage and current at the point of common coupling (PCC) under normal operating conditions. The source voltages are also estimated simultaneously. The estimation method is based on Least Squares (LS), using the Orthogonality Principle in complex Hilbert space to deal with complex variables directly. By simulations, the influence of measurements noise on the estimation accuracy at fundamental and harmonic frequencies is investigated in detail.