Operational flexibility and system dispatch

With the increasing penetration of variable resources, the system operators are facing increasing amount of variability during the real-time system operation. System operators usually adopt load following control such as look-ahead short-term unit commitment, real-time economic dispatch and automatic generation control to maintain system balance. All of these control actions require the system to have enough flexibility to accommodate the variation caused by these uncertain factors. The higher degree of system flexibility is, the higher amount of variability the system can tolerate. Facing the increasing amount of uncertainty, system operators are more concerned about the flexibility of the system. Such questions as “does the system has enough ramping capability to recover in a high-speed wind cut-out event”, and “how much wind power generation can the system tolerate without causing any transmission issues” rise naturally. It would be desirable to alert the system operator about how flexible the system is to respond to certain event such that preventive actions can be performed in advance. This calls for a formal definition of operational flexibility, its metrics and the corresponding computational methodology. This paper investigates these topics, and one of flexibility applications in the system dispatch.