Contents I. Introduction
Power systems are of large scale in nature and distributed over large geographic areas. A huge number of controls is applied throughout the system not just to balance the electric power demand and supply but also to counteract severe disturbances that can create dynamic stability problems in a fraction of a second [1]. Many different devices and design techniques have been investigated to improve transient stability and damping characteristics [2], [3]. The dynamics of power systems following considerable structural changes and loading conditions need to be controlled to ensure the integrity of the system. Design of excitation systems and voltage control has been the most cost-effective means of achieving improved system stability and reliability. Nonlinear control design techniques have gained significant attention due to their inherent ability to improve control performance beyond what can be achieved with linear control. Nonlinear control theory provides the tools necessary to improve dynamic performance while advances in computer systems and signal processing allow a practical implementation. This has the potential to result in a more reliable and secure electric power supply.
