Variable time step, implicit integration for extended-term power system dynamic simulation

This paper describes the development of a variable time step algorithm for the numerical simulation of power system phenomena spanning time periods from several seconds to several hours. The algorithm automatically reduces the time step of integration to capture fast transients and increases it when the system variables are varying slowly. The solution algorithm is based on a numerically stable, implicit, low order integration similar to the trapezoidal rule. Computer simulation results for two scenarios are presented. These scenarios are: a severe power system load ramp leading to voltage collapse; and a six-hour operational cycle