Variable-speed operation of hydropower plants: Past, present, and future

This paper reviews state-of-the-art in variable-speed operation of hydropower plants, the focus being on pumped-storage hydro. Relevant literatures are reviewed to address the benefits of variable-speed operation to both power system and hydropower plants. Two main configurations (i.e. DFIM and CFSM) to enable variable-speed operation are discussed and compared. Addressing the technology status and energy policies in the past, present and future, the paper points out how motivation, services, value and technology of variable-speed hydropower plants have been subject to considerable changes.