8.1 Introduction

The current operating environment of a fossil fuel power unit (FFPU) is characterised by many needs and requirements. First, a FFPU must support the main objective of the power system, which is to meet the load demand for electric power at all times, at constant voltage and at constant frequency (Elgerd, 1971). In addition, competition among utilities and other market driven forces has increased the usage of FFPUs in load-following duties (Armor, 1985). Moreover, stringent requirements on conservation and life extension of major equipment, and regulations on reduced environmental impact, have to be fulfilled (Divakaruni and Touchton, 1991). This context may be synthesised as an essential requirement for a FFPU to achieve optimal and robust wide-range load-following operation under multiple operation objectives, such as minimisation of load tracking error, minimisation of fuel consumption and heat rate, maximisation of duty life, minimisation of pollutant emissions, etc. (Garduno-Ramirez and Lee, 2001a).

Effective participation of a FFPU in load-following duties requires the ability to undertake large variations in the power being generated in the form of daily, weekly, and seasonal cycles, as well as random fluctuations about those patterns. The major courses of action that have been undertaken to facilitate wide-range load-following operation with improved performance include upgrading the physical components of the power unit and the control system (Miller and Sterud, 1989). Since wide-range operation imposes strong physical demands on the unit equipment, which inherently lead to conflicting operational and control situations, the load-following...