Frequency-Dependent Impedance Modeling Of Power Grid With High Power Electronics Penetration

With increasing penetration of high performance power electronic devices such as the flexible DC transmission and renewable energy power generation system, the Thevenin equivalent of the power grid at fundamental frequency fails to reflect the actual grid impedance change completely. Considering the practical situation when a large-capacity rectifier is connected to a distribution grid, we derive the expression of its Thevenin equivalent parameters, including the grid voltage and impedance are given at different frequencies, by adopting the multi-time section method. A simple IEEE 9-Bus system with an uncontrolled rectifier is analyzed in this paper. It is found there is a nonlinear relationship between the equivalent impedance and the frequency. The analysis results are proved to be correct through maximum power transmission simulation based on the impedance module margin method.