Large-scale hydrogen electrolyzers for hard-to-abate industries, such as steel industry, have the potential to be an essential tool of demand response in low inertial power systems with high shares of renewable energies. Their flexibility comes from the possibility to store hydrogen, decoupling electric consumption from hydrogen demand. Therefore, they can help in the integration of more renewable energies by the provision of grid services, such as frequency regulation. Alkaline electrolyzers (AELs) are the most mature and cost effective technology for large-scale hydrogen applications. However, their slow dynamics do not allow a fast response. Therefore, their combination with energy storage systems (ESSs) into hybrid hydrogen systems (HHSs) enhances their flexibility and fast response for frequency regulation. Supercapacitors (SCs) are suitable ESS technology in this application due to the high power and low energy required. A decentralized dynamic power sharing control is proposed for an AEL/SC HHS to provide frequency regulation with scalability. The control strategy respects the slow dynamics of the AEL, while the use of the SC is optimized by the automatic recovery of the dc bus voltage and SC state of charge (SoC). The decentralized approach of the control strategy enables easy expansion of the system, essential for large-scale hydrogen systems. The effectiveness of the method in large-scale power systems, as well as its scalability is shown in simulation results. The control strategy is validated with experimental results.

Large-scale water electrolyzers have the ability to operate as flexible loads, absorbing power fluctuations in power systems with high or full share of variable renewable energy sources (VRESs). For large-scale industrial applications, alkaline water electrolyzers (AWEs) and thyristor-based power converter topologies are commonly used due to their lower cost compared to proton exchange membrane water electrolyzers (PEMWEs) and transistor-based topologies. However, thyristor-rectifiers have a significant ripple when operated at partial load. A wide operational range is required when electrolyzers operate in a flexible manner, and large current ripples due to the power converter topology increase the power losses in the electrolyzer. Therefore, it is essential to study the impact of the current ripple on AWE performance. This article proposes an evaluation approach to systematically assess the impact of different power converter topologies on AWE losses, including an electrolyzer model for power electronic applications and experimental verification. Realistic current waveforms for industrial applications are obtained from a simulated large-scale electrolyzer system, and these waveforms are tested in a small-scale experimental setup. The experimental results validate the large-scale system simulations and the proposed model and provide quantitative assessment of AWE losses caused by the current ripple. The results also show that the six-pulse thyristor rectifier has the highest current ripples, causing the highest additional losses in the electrolyzer.

Hydrogen electrolyzers are promising tools for frequency regulation of future power systems with high penetration of renewable energies and low inertia. This is due to both the increasing demand for hydrogen and their flexibility as controllable load. The two main electrolyzer technologies are Alkaline Electrolyzers (AELs) and Proton Exchange Membrane Electrolyzers (PEMELs). However, they have trade-offs: dynamic response speed for AELs, and cost for PEMELs. This paper proposes the combination of both technologies into a Hybrid Hydrogen Electrolyzer System (HHES) to obtain a fast response for frequency regulation with reduced costs. A decentralized dynamic power sharing control strategy is proposed where PEMELs respond to the fast component of the frequency deviation, and AELs respond to the slow component, without the requirement of communication. The proposed decentralized approach facilitates a high reliability and scalability of the system, what is essential for expansion of hydrogen production. The effectiveness of the proposed strategy is validated in simulations and experimental results.

Hydrogen is a key technology for the decarbonization of industrial sectors, such as steel industry. These industries requires large-scale electrolyzers, which are able to operate as flexible loads. This is thanks to the possibility of storing the hydrogen, and decouple the electricity consumption from the hydrogen demand. These flexible loads are an a essential tool to provide grid services, such as frequency regulation, in future power systems with a high share of renewable energies. However, to provide an overall fast response for frequency regulation, large-scale electrolyzers need to be combined with Energy Storage Systems (ESSs), such as battery systems, in Hybrid Hydrogen Systems (HHSs). Furthermore, the combination of different electrolyzer technologies, with Alkaline elec-trolyzers (AELs) and Proton Exchange Membrane Electrolyzers (PEMELs) as the dominant commercial technologies, can reduce the need and investment on ESSs. A power sharing control for frequency regulations using HHSs is proposed to achieve an overall fast system response, and maximize the advantages of the combination of AELs, PEMELs and ESSs. Simulations and experiments have been conducted to validate the effectiveness of the proposed control strategy for HHSs.

The SMall Aspect Ratio Tokamak (SMART) is a new spherical machine that is currently under construction at the University of Seville aimed at exploring negative vs positive triangularity prospects in Spherical Tokamaks (ST). The operation of SMART will cover three phases, with toroidal fields Bϕ≤ 1 T, inductive plasma currents up to Ip= 500 kA and a pulse length up to 500 ms, for a plasma with R = 0.4 m, a = 0.25 m and a wide range of shaping configurations (aspect ratio, 1.4 < R/a < 3, elongation, κ≤ 3, and average triangularity, -0.6 ≤δ≤ 0.6). The magnet system of the tokamak is composed by 12 Toroidal Field Coils (TFC), 8 Poloidal Field Coils (PFC) and a Central Solenoid (CS). With such operating conditions, the design of the central stack, usually a critical part in spherical tokamaks due to space limitations, presents notable challenges. The current SMART central stack has been designed to operate up to phase 2 and it comprises the inner legs of the TFC, surrounded by the CS, two supporting rings, a central pole and a pedestal. To achieve the plasma parameters of this phase (Bϕ=0.4 T with inductive Ipup to 200 kA), the high currents required, combined with the low aspect-ratio of the machine lead to high forces on the conductors that represent an engineering challenge. The loads expected in the central stack are a centring force up to 1.5 MN and a twisting torque up to 7.4 kNm. This work describes the design of the central stack and its mechanical validation with a multiphysics finite element assessment. Using a combined electromagnetic and mechanical assessment, it is shown that the SMART central stack will meet the physics requirements in phase 2.

The increase in hydrogen production to support the energy transition in different sectors, such as the steel industry, leads to the utilization of large scale electrolyzers. These electrolyzers have the ability to become a fundamental tool for grid stability providing grid services, especially frequency regulation, for power grids with a high share of renewable energy sources. Alkaline electrolyzers (AELs) have low cost and long lifetime, but their slow dynamics make them unsuitable for fast frequency regulation, especially in case of contingencies. Proton Exchange Membrane electrolyzers (PEMELs) have fast dynamic response to provide grid services, but they have higher costs. This paper proposes a dynamic power allocation control strategy for hybrid electrolyzer systems to provide frequency regulation with reduced cost, making use of advantages of AELs and PEMELs. Simulations and experiments are conducted to verify the proposed control strategy.

A new spherical tokamak, the SMall Aspect Ratio Tokamak (SMART), is currently being designed at the University of Seville. The goal of the machine is to achieve a toroidal field of 1 T, a plasma current of 500 kA and a pulse length of 500 ms for a plasma with a major radius of 0.4 m and minor radius of 0.25 m. This contribution presents the design of the coils and power supplies of the machine. The design foresees a central solenoid, 12 toroidal field coils and 8 poloidal field coils. Taking the current waveforms for these set of coils as starting point, each of them has been designed to withstand the Joule heating during the tokamak operation time. An analytical thermal model is employed to obtain the cross sections of each coil and, finally, their dimensions and parameters. The design of flexible and modular power supplies, based on IGBTs and supercapacitors, is presented. The topologies and control strategy of the power supplies are explained, together with a model in MATLAB Simulink to simulate the power supplies performance, proving their feasibility before the construction of the system.

The SMall Aspect Ratio Tokamak (SMART) device is a new compact (plasma major radius Rgeo≥0.40 m, minor radius a≥0.20 m, aspect ratio A≥1.7) spherical tokamak, currently in development at the University of Seville. The SMART device has been designed to achieve a magnetic field at the plasma center of up to Bϕ=1.0 T with plasma currents up to Ip=500 kA and a pulse length up to τft=500 ms. A wide range of plasma shaping configurations are envisaged, including triangularities between −0.50≤δ≤0.50 and elongations of κ≤2.25. Control of plasma shaping is achieved through four axially variable poloidal field coils (PF), and four fixed divertor (Div) coils, nominally allowing operation in lower-single null, upper-single null and double-null configurations. This work examines phase 2 of the SMART device, presenting a baseline reference equilibrium and two highly-shaped triangular equilibria. The relevant PF and Div coil current waveforms are also presented. Equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.

The SMall Aspect Ratio Tokamak (SMART) is a new spherical device that is currently being designed at the University of Seville. SMART is a compact machine with a plasma major radius () greater than 0.4 m, plasma minor radius () greater than 0.2 m, an aspect ratio () over than 1.7 and an elongation () of more than 2. It will be equipped with 4 poloidal field coils, 4 divertor field coils, 12 toroidal field coils and a central solenoid. The heating system comprises of a Neutral Beam Injector (NBI) of 600 kW and an Electron Cyclotron Resonance Heating (ECRH) of 6 kW for pre-ionization. SMART has been designed for a plasma current () of 500 kA, a toroidal magnetic field () of 1 T and a pulse length of 500 ms preserving the compactness of the machine. The free boundary equilibrium solver code FIESTA [1] coupled to the linear time independent, rigid plasma model RZIP [2] has been used to calculate the target equilibria taking into account the physics goals, the required plasma parameters, vacuum vessel structures and power supply requirements. We present here the final design of the SMART vacuum vessel together with the Finite Element Model (FEM) analysis carried out to ensure that the tokamak vessel provides high quality vacuum and plasma performance withstanding the electromagnetic  loads caused by the interaction between the eddy currents induced in the vessel itself and the surrounding magnetic fields. A parametric model has been set up for the topological optimization of the vessel where the thickness of the wall has been locally adapted to the expected forces. An overview of the new machine is presented here.

The SMall Aspect Ratio Tokamak (SMART) device is a novel, compact (Rgeo = 0.42 m, a = 0.22 m, A 1.70) spherical tokamak, currently under development at the University of Seville. The SMART device is being developed over 3 phases, with target on-axis toroidal magnetic fields between 0.1 ≼ Bf ≼ 1.0 T, and target plasma currents of between 35 ≼ Ip ≼ 400 kA; with phases 2 and 3 enabling access to a wide range of elongations (κ ≼ 2.30) and triangularities (− 0.50 ≼ δ ≼ 0.50). SMART employs four internal divertor coils with two internal and two external poloidal field coils, enabling operation in lower-single, upper-single and double-null configurations. This work examines phase 3 of the SMART device, presenting a prospective L-mode discharge scenario without external heating, before examining five highly-shaped equilibria, including: two double null triangular configurations, two single null triangular configurations and a baseline double null configuration. All equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.