Grid impedance identification using SiC-Jfet switch-module

The grid impedance identification is important to evaluate the effect on the power quality by renewable energy sources using inverters. It can also be used for improved design of existing grid-side filters and the control parameters for the inverters. One approach to determine the grid impedance is based on the switching of an ohmic load. The resulting transients caused by this switching can be used to calculate the frequency dependent grid impedance. In this paper the development of a switch using SiC-Jfets is presented. With this switch high switching frequencies and adjustable slopes within certain limits can be generated which is important for a precise identification of the grid impedance. Measurements of the first 6 kV prototype and the design for the required gate driver are presented.