Drivetrain Architectures for a Mechanically Decoupled Contra-Rotating Reversible Pump-Turbine

With the rise of renewable energy production in the pan-European grid, the need for flexible energy storage is experiencing a rapid increase. Pumped hydropower storage has proven viability due to its long lifespan and cost-effectiveness. The ALPHEUS project will implement pumped hydropower storage for flat topographies to augment grid stability in adjacent regions. To ensure optimal efficiency and fast switching times in these low head applications, a contra-rotating axial Reversible Pump-Turbine (RPT) is designed. The runners will be driven by two separate Axial-Flux Permanent Magnet Synchronous Motors (AF-PMSM) to ensure optimal efficiency and flexibility at variable speed and flow rate. In this new setup, great attention is needed for the drivetrain architecture. The AF-PMSMs can be placed either outside or inside the water tube, using respectively tube elbows or bulbs. Furthermore, coaxial shafts allow the machines to be placed together, on one side of the RPT. This paper proposes four drivetrain architecture concepts, which are evaluated qualitatively based on their influence on RPT and AFPMSM performance as well as bearing arrangement.