Variable-speed Pumped Hydro Storage Technology: Overview, Solutions and Case Studies

As the most mature and economical large-scale energy storage technology, pumped hydro storage is one of the important technical means to improve the flexibility of the grid and the penetration level of renewable energies. Compared to traditional constant-speed pumped hydro storage units, variable-speed pumped hydro storage units have obvious advantages in active power regulation and reactive power compensation under the pump operational mode, which thus better match the output fluctuations of renewable energies and absorb them. This paper evaluates the system configuration and operating characteristics of two technical solutions for variable-speed pumped hydro storage: Doubly-Fed Induction Machine (DFIM) and Converter-Fed Synchronous Machine (CFSM). A technical overview and comparison are described between constant-speed and two variable-speed solutions, DFIM and CFSM. Two case studies of CFSM application in Switzerland and Austria are also introduced in detail.