Rigidity concept for stabilizing transient processes in power systems

This paper introduces a totally new concept of rigidity and its first example applications for stabilizing transient processes in power systems. By the authors´ definition, a rigid system maintains a close-to-original state despite passing disturbances or smoothly goes over to a new state if the disturbances are permanent; it responds to faults and disturbances with a smooth monotonous or minimum oscillatory behavior. Rigidity implies stability. A rigid system is stable because it applies all state variables to be at least bounded. In contrast to stability, rigidity has a quite simple and convenient mathematical description. It provides an objective function that can be optimized along the transient trajectory to obtain effective stabilizing control impacts. Several different online control actions can be selected in coordination for a variety of operating conditions, controlled variables and uncertainties. The rigidity criterion can be easily computed by using the output files of any transient simulation program.