In the face of the significant source-load uncertainty caused by the large-scale development of renewable energy and the re-electrification of energy consumption

and the urgent need to improve the utilization efficiency of the existing large-scale assets in power systems

the trends towards flexibility in AC transmission and distribution systems have become increasingly prominent. This paper proposes the concept and elaborates on the connotation of flexible AC transmission & distribution technology(FTDT)

and introduces two major categories of flexible technologies and their fundamental functionalities: one dominated by power electronic devices

and the other based on electromagnetic equipment. FTDT extends the scope of traditional FACTS technologies by expanding their application to distribution systems and incorporating flexibility solutions based on electromagnetic equipment. FTDT will provide solutions and equipment supports for the construction of new-type power systems

enabling their safe

reliable

and efficient operation.