Review of Grid Impedance Estimation for Gird-Connected Inverter

The performance of grid-connected inverter is closely related to the grid impedance in distributed power generation systems. However, the grid impedance usually varies with the change of the grid operation condition.Therefore, accurate grid impedance estimation is one of the key technologies to achieve the high performance adaptive control of the inverter which connects to a weak grid. Recently, many literatures proposed and studied the methods for grid impedance measurements. However, the merits and demerits of different methods have not been discussed deeply. For this reason, this paper presents a review of the various methods for grid impedance measurement. The existing methods are classified into three main categories: active methods, passive methods and quasi-passive methods. Moreover, the characteristics of these methods are investigated, and the merits and demerits and suitable application of each method are also discussed. At last, some issues to be solved are pointed out.