Power Grid Integration of GigaWatt-scale Hydrogen Production

Abstract

Abstract Climate change is one of the most pressing issues that humanity faces today. The urgent need to mitigate green-house gas emissions has triggered an unprecedented expansion of renewable energy sources, consequently, creating an opportunity to revolutionize our energy systems. In this context, green hydrogen emerges as a potential candidate to decarbonize hard-to-electrify industries, such as iron & steel, high-temperature heat applications, petrochemical, transport and aerospace sector. This thesis endeavors to explore the technical feasibility of gigawatt scale hydrogen production by examining a proposal of plant design, implementing a model for electrolyzer systems available in the market and selecting an AC/DC topology for the rectifier. The elected station is connected to the HVAC transmission grid through a step-down distribution system with two voltage levels, 400 and 33 kV. This grid is assumed to have a high short circuit capacity given the high demand of power and its design needs to comply with grid code requirements and international standards (IEC, IEEE). The driver for standardization and cost savings, while matching electrolyzer’s technology with adequate electrical infrastructure, led to the decision of implementing alkaline water electrolyzers. Besides, an accurate model definition required a solid understanding of the electrical and thermal fundamentals of electrolysis. The electrolyzer voltage and current requirements defined the criteria for selecting the converter’s topology. The final choice was the 12-pulse thyristor rectifier given its high efficiency, reliability and good control of the current. Low-order harmonic cancellation excluding those harmonic orders with 12h±1 with h = 1, 2, 3 ... was an attractive feature, but required the use of tuned-LC filters for the 11th-13th and 23rd-25th harmonics. A look-up table is implemented for the electrolyzer model next with a per-unit current controller for the 12-pulse thyristor rectifier. This set-up makes it easily reimplementable in future projects, since it enables the implementation of this controller for any electrolyzer system, independently of its specifications. All models and simulations are performed using the power system analysis software DIgSILENT PowerFactory. Finally, the correct rating of different components used in the station and grid code compliance was verified performing different simulations: a load flow analysis, a dynamic ramp-up simulation to nominal capacity and lastly transient analysis of the station in spontaneous events like load rejection.