The concept of flexibility has been described by researchers. At present, studies on power system flexibility can be categorized into short-term operational flexibility and long-term planning flexibility. However, despite above categorization, there is no comprehensive defnition of power system flexibility. Each research group has presented its defnition based on main feld of the study approach. Accordingly, in this chapter, flexibility has been defned as a network’s ability to regulate generation and demand concerning intentional or unintentional deviations. From the operational viewpoint, flexibility can be addressed as the capability of a power system to be applied to a specifc time under net demand alterations. In past few years, flexibility enhancement of distribution network for an intelligent emergency operation has become an essential concern for power and energy researchers. About more than 70% of power outages are due to contingencies in distribution systems (DSs). DSs are imperative for innovative emergency operation strategies which employ available resources in a more reliable and corporative way to improve flexibility of the system. The prevalent solutions such as integration of sustainable energy resources and storages, microgrid (MG) development, and power line strengthening can be employed in the current DSs. Out of above-noted prevalent solutions, applying the MGs for flexibility enhancement is more desirable. This is because of the facility of MGs to corroborate the integration of the renewable energy sources (RESs) and potential of islanding scheduling (i.e., potentiality to survive their critical loads in the contingencies). During emergency operation, the on-fault area can be isolated from the entire network and subdivided into some independent MGs through the tie-line switches.In this chapter, the concept of flexibility in DSs, the occurrence of emergency, and general strategies for enhancing the flexibility of the DSs are reviewed at frst. Then, the confguration of the MGs is investigated. The general roles and approaches applied by MGs for enhancing the flexibility of the DSs in single, networked, and multi-energy system frameworks, the corresponding communication flexibilities, and the decision-making framework in DS with MGs are presented separately in four sections. The islanding strategy and DRPs are also investigated for an emergency operation. Applying various mobile and stationary power generation sources, their impacts on the DS flexibility, and the corresponding constraints during emergency operation are evaluated in a series of sections.
