Variable speed pumped hydro storage: A review of converters, controls and energy management strategies

The increasing share of renewables in the power generation mix makes the power system volatile to uncertain meteorological conditions. The stochastic nature of renewables demands energy storage systems (ESS) to maintain the stability of the grid. Among various ESS, pumped hydro storage (PHS) is a technically matured and economically viable option for large scale energy storage. However, it has not gained much attention from researchers due to its technical maturity and site-specific nature. Lately, the focus is shifting towards the development of variable speed PHS and different reservoir schemes to realize PHS with the existing infrastructure. Nevertheless, the development of variable speed PHS necessitates a proper selection of power converter topology with a suitable control technique. Thus, the principal objective of this paper is to present a critical review of different levels of control of the variable speed PHS. Firstly, a state of the art comparison between PHS and other ESS is presented through critical data analysis using Tableau software. Secondly, the control strategies are categorized into a hierarchical structure and reviewed based on a bottom-up approach. Towards the end, a synoptic review is presented to elucidate the dominating strategy at each level of the control hierarchy. Finally, the domains which require further attention are distinctively reported to leverage the future research of PHS.