A Low-order Frequency Response Model of Adjustable-Speed Pumped Storage Unit

Rocketing penetration of the renewable and intermittent sources into the power system results in critical frequency stability challenges. As the mature and massive-scale energy storage technology, the pumped storage plant is considered as an effective solution. The advanced adjustable-speed pumped storage unit has greater flexibility for frequency regulation compared to traditional fixed-speed pumped storage unit, so it is crucial for frequency stability to clarity the intrinsic dynamics of frequency response of adjustable-speed pumped storage unit and to establish its physics-based model, which have been studied inadequately. To reveal the intrinsic performance and present an analytical expression, this study proposes that the additional power obtained by primary frequency control of adjustable-speed pumped storage unit is jointly supplied by electric component and mechanical one. Then based on this, a low-order frequency response model of adjustable-speed pumped storage unit is established, which only retains the characteristics of frequency responsive governor and reversible pump-turbine. Finally, the proposed model is validated by comparing its simulated frequency response with that of the full model by PSCAD tool.