A Grid Impedance Identification Method Based on Complex Coefficient Filter Considering DC Offset Effects

For the purpose of acquiring the accurate grid impedance, a complex coefficient filter (CCF) based grid impedance identification method is studied in this paper. High frequency non-characteristic harmonic voltages and currents are injected into the power grid by the power converter firstly. Next, a CCF is used to extract these high frequency voltages and currents from the sampled voltages and currents at the point of common coupling. Then, the grid impedance is calculated based on the extracted voltages and currents. Considering that the impacts of the DC offset on the grid impedance identification cannot be removed by the conventional CCF, an improved CCF is proposed in this paper by adding a high-pass filter to the forward channel of the conventional CCF. The filter characteristic of the proposed CCF is analyzed, which shows its DC offset suppression capability. Simulation results show the effectiveness of the proposed grid impedance detection method.