A New High Frequency Grid Impedance Estimation Technique for the Frequency Range of 2 to150 kHz

Abstract

Grid impedance estimation is used in many power system applications such as grid connected renewable energy systems and power quality analysis of smart grids. The grid impedance estimation techniques based on signal injection uses Ohm's law for the estimation. In these methods, one or several signal(s) is (are) injected to Point of Common Coupling (PCC). Then the current through and voltage of PCC are measured. Finally, the impedance is assumed as ratio of voltage to current signals in frequency domain. In a noisy system, energy of the injected signal must be sufficient for an accurate approximation. However, power quality issues and regulations limit the energy and the voltage levels of the injected signal. There are three main issues in impedance estimation using signal injection: I) Power quality of grid, II) frequency range of estimation, and finally III) accuracy of estimation. In this paper, the stationary wavelet denoising algorithm is employed instead of increasing the energy of injection signal(s). In the paper, a novel method is proposed for impedance estimation based on selecting several appropriate injection signals and denoising the measured signals. The proposed method is able to impedance estimation in a wide frequency range without any effect on power quality. Finally, simulation results have been carried out to validate the proposed method.