This package calculates the system trajectories of the Illinois power grid under different voltage dampings in the nominal operating scenarios. To perform, please follow the instructions below. 1. You first need the MATPOWER package, which can be obtained from https://matpower.org/ 2. Put all files in the package in the same folder. And add matpower package into the MATLAB searching path. 3. Run the main.m by MATLAB 2019a or higher versions.