Pumped storage plants (PSPs) are considered as the most mature and reliable technology for bulk storage energy with low CO2 footprint. With the massive integration of variable renewable energy sources and power electronic devices, transmission system operators (TSOs) need more flexibility to ensure a secure supply of the electrical energy. From an electricity generation company standpoint, this represents a diversification of income sources since new markets as fast frequency services tend to emerge. Although, they can balance the grid power by consuming or providing energy, the main drawbacks of PSPs are their low time response that makes them unable to access to these new remuneration mechanisms. One of the considered solutions to increase the flexibility of PSPs, and unlock the provision of dynamic ancillary services, is to hybridize the hydropower plant with a stand-alone energy storage system (ESS) using technologies like batteries or supercapacitors.
However, the little space available in hydropower stations and environmental constraints can make access difficult to such a solution. Traditionally, reversible PSPs work with fixed-speed machines. A static frequency converter (SFC) is commonly used to start a group in pump mode. In that perspective, the proposed paper presents an innovative concept of enhanced static frequency converter (E-SFC). It consists in integrating the ESS directly in the SFC of the plant to mutualize equipment, with a dual use of the power converter. It also provides an opportunity to reduce the overall capital expenditure in comparison with a conventional ESS connected to the point of coupling of the medium voltage grid of the plant.
The paper is organized as follows. Section 1 presents the need of flexibility from a hydroelectric power plant to fit with the growing needs and new ancillary services emerging worldwide. In Section 2, the innovative solution of SuperGrid Institute to hybridize a PSP, and to keep the existing hydropower fleet with a key role in the future power markets, is presented. In section 3, the need of synergistic control methods to operate hybrid power plant is exposed. Section 4 depicts the experimental results of the hybridization of a PSP on a real time power hardware in the loop (PHIL) test rig. Finally, section 5 concludes and highlights the advantages of the proposed solution.
Florian Errigo, Florent Morel, Hugo Mesnage and Renaud Guillaume
Presented at Hydro 2023