Advanced Grid-Forming Undersea Pumped Storage to Enable 100% Renewable Offshore Oilfield Power Systems

To advance carbon reduction of the offshore oilfield power system (OOPS), the grid-forming undersea pumped storage system (GFM-UPSS) emerges as a promising solution. This paper introduces a novel framework for a 100% renewable OOPS utilizing the GFM-UPSS. Firstly, the control strategy of the GFM-UPSS is presented. It consists of the grid-side converter (GSC), machine-side converter (MSC), and reversible pump-turbine (RPT) to achieve frequency and voltage regulation. A steady-state model is then developed detailing the water head, power, and volume of the spherical shell. In addition, the paper explores the converter parameter impacts on the GFM-UPSS transient model and derives the closed-form solutions. With the steady-state model, an optimal sizing method is presented and economic advantages in the marine environment are studied for the GFM-UPSS. Finally, EMT simulations are conducted to assess the frequency & voltage stabilities and verify the effectiveness of the GFM-UPSS in enabling a 100% renewable OOPS. The optimal sizing results show that construction costs, mainly for OWP, are dominated and are influenced by sphere radius, placement depth, and start-stop cycles, while a 2.5 capacity ratio between OWP and GFM-UPSS consistently emerges as optimal. Moreover, analysis of transient stability shows that it improves with higher frequency & voltage modulation coefficient and lower virtual impedance. The impact of RPT and MSC, mainly on frequency regulation, is determined by the DC droop coefficient and turbine inertia.