An energy based approach to undervoltage load shedding

A novel effort to apply Lyapunovʹs energy methods towards developing an energy based load shedding scheme in order to alleviate voltage instability is presented. An ‘absolute’ energy function is derived which eliminates the need to calculate the unstable equilibrium points (UEPs) and thus saves a considerable amount of computation time. The localized and zonal nature of early voltage instability symptoms is studied and exploited. The functions are then used to generate three-dimensional (3-D) security region plots. Based on the proximity of the system state to the stability boundaries (that can be mapped on the 3-D plots), load shedding decisions can be carried out. The sensitivity of the derived energy measure with respect to the real and reactive loads is also calculated. From these sensitivity measures, a quantitative yardstick is obtained that determines the proportions of real and reactive load to be shed. The method is computationally efficient and is easily interpreted, demonstrating a strong potential for real-time monitoring and control application.