Optimal Tie-Line Control

Abstract

For more than two decades, the problem of load frequency control (LFC) using conventional or advanced-control theory has been the subject of numerous studies. The conventional LFC approach often employs what is called the tie-line bias concept to design a system controller that has a proportional-plus-integral (PI) action. This type of control is used extensively in practice in preference to all the techniques that have been proposed recently, employing modern control theory. The reason for that is that most recent techniques have developed linear feedback controls that are functions of all the system state variables as well as the system disturbances (Refs. 5.1, 5.2). Therefore, it was necessary to design an observer to realize these kind of controls (Ref. 5.3). Once an observer is introduced into the system, the cost is increased, and the control is no longer optimal (Ref. 5.4). Another important reason is that a control that depends upon all the system states needs some of these state variables to be telemetered, since the areas of interconnected power systems (IPS) are spread over large geographical territories. This is why, in practice, control engineers prefer to use the conventional control to the advanced one, in spite of the contention that the latter improves the system transient performance.