Enhanced harmonic state estimation in unbalanced three-phase electrical grids based on the Kalman filter and physical scale-down implementation

•Harmonic state estimation is based on limited measurements and the half-wave symmetry property.•The periodic state is obtained using the Kalman filter and synchronized measurements.•The method adequately processes the data given by a limited number of measurements.•The harmonic state of unbalanced three-phase electrical power grids is assessed.•The estimation results are validated by comparing them against experimental data.