With an 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 fre-quency fails to reflect actual grid impedance changes completely. Considering the practical situation of large-capacity rectifier is connected to a distribution grid, 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 isn’t a positive 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.
