Simulating voltage collapse dynamics for power systems with constant power load models

Electromechanical transients are studied using transient stability simulators with differential-algebraic equation (DAE) models employing phasor network variables. While these simulators can follow the electromechanical transients (e.g., voltage and power swings) due to large disturbances with loads modeled as constant impedance, they may fail to converge under voltage collapse conditions for systems with constant power load models. This non-convergence has been attributed to a voltage collapse during the transient in the literature. This paper aims at addressing this non-convergence issue of the phasor based transient stability simulators using constant power load models. It presents a methodology for examining the voltage collapse trajectories by modeling constant power loads as voltage dependent impedance loads. Simulations on a two bus and a nine bus system for line switching disturbances show that the voltage collapse trajectories can be examined via the proposed voltage dependent impedance load model.