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Water electrolysis systems accelerate the green transition in Danish power, notably via mature alkaline electrolyzers integrated with renewables. The demand for clean and sustainable energy sources has spurred significant interest in electrolysis for hydrogen production. Electrolyzers play a pivotal role in this context, and efforts to scale up their operation are central to meeting the growing hydrogen demand. This study develops MATLAB/Simulink models of various-sized alkaline electrolyzers to design large hydrogen plants, assessing their scalability and economic viability.

This paper presents grid-code considerations that must be addressed when connecting large electrolyzer plants to the electrical grid. A model for an electrolyzer module based on a grid-connected three-phase H-bridge converter is presented, together with a scaling method, for investigating relevant aspects. A low-voltage-ride-through strategy is implemented into the converter and the performance of the strategy is tested against running the system with no low-voltage-ride-through strategy. Finally, the paper will conclude on the ability of the electrolyzer plant to provide reactive power support and the considerations that must be made if this support is desired.

Alkaline electrolyzers (AELs) have emerged as promising candidates for providing flexible grid services. However, a comprehensive understanding of their operational flexibility has been hindered by a lack of consideration of their thermodynamics in previous studies. To address this limitation, this paper presents comprehensive models that analyze the impact of AEL thermodynamics on their operational flexibility. Specifically, a closed-loop thermal model with temperature-stabilizing control is established to capture the temperature evolution, followed by the development of a temperature-dependent U–I model to characterize the influence of temperature on electrical performance. Case studies are conducted to simulate a practical 26 kW AEL facility using Matlab/Simulink. The results demonstrate that the proposed temperature-stabilizing control effectively maintains the temperature at the setpoint when adjusting the power consumed by AELs. Consequently, the power regulation range of AELs increases from 7.4 kW to 16 kW, compared to a simple control that fixes the cooling water flow at 0.02 m3/h. While increasing the fixed water flow to 0.05 m3/h can also enhance the regulation capacity, the proposed control ensures higher system efficiency than that of the fixed flow control. Moreover, the temperature-stabilizing performance of the controller is influenced by the cooling system’s parameters. Hence, a coordinated design approach between the cooling system and temperature controller is recommended to achieve favorable temperature-stabilizing performance.

Hybrid energy storage system (HESS) is an effective measure to improve the electrical performance of naval DC microgrids supplying power pulsed loads (PPLs). Coordination control scheme and capacity configuration of the HESS are two key issues to meet multiple control objectives and constraints. In response to the requirements of optimal operation for HESS under various complex scenarios, a dual model predictive control (D-MPC) strategy is proposed for the HESS integrated with the superconducting magnetic energy storage (SMES) and battery in this paper. Firstly, the current reference of battery is obtained through the MPC integrated adaptive low-pass filtering (ALPF). Then the local MPC controller of HESS converter is utilized to track the current reference of battery and SMES as well as the bus voltage reference to achieve transient power allocation of HESS and energy balancing of DC microgrid. Meanwhile, a cost function with adaptive weighting factor is designed to make tradeoff of conflict control objectives. Furthermore, the HESS capacity configuration and superconducting magnet optimal design according to its actual operation condition are presented. Comparative case studies are conducted in HIL experiment to demonstrate the superiority of the proposed scheme in terms of improving system operation performance under various PPLs.

Integration of the hydrogen sector into power systems via electrolyzers could greatly facilitate energy sustainability by producing green hydrogen, moreover, assist in reinforcing frequency stability based on optimal control of electrolyzers. In order to improve the frequency performance of the wind-dominated electricity-hydrogen systems (WEHS), this paper investigates how to analytically evaluate and implement the dynamic frequency regulation (DFR) supported by a grid-scale alkaline electrolyzer (AEL) plant. The DFR's potential of the AEL plant is released by an emulated power-frequency characteristic, and its contributions to improving system frequency response are also analytically evaluated from the aspects of transient, steady-state, and stability indicators. Furthermore, the DFR dependency on the frequency containment reserve provision and pre-contingency operating points of AELs are analytically clarified. A DFR-driven controller to coordinate multiple modules in the AEL plant is also designed in detail. In addition, the economic analysis is presented to evaluate the profitability of AELs providing frequency support. Cases of a simple WEHS and a modified IEEE 9-bus system integrated with grid-scale AEL plants during frequency contingencies are studied to validate the proposed DFR method, which can improve the system frequency response with smoother transients and lower steady-state deviation.

The transition to green energy, driven primarily by renewables, is imperative as fossil fuels deplete and their environmental impact worsens. However, integrating renewables effectively into existing energy systems is challenging due to their intermittent and fluctuating nature. The emergence of power-to-hydrogen (PtH2) technologies offers a promising pathway to efficiently facilitate renewables integration from a cross-sectoral perspective. To this end, it is essential to understand the principles of PtH2 technologies and investigate their role in accelerating the integration of renewable energy sources. The main objective of the thesis is to investigate the modeling and control aspects of PtH2 technologies in the context of renewable energy systems (RENSs). Drawing insights from seven papers, the thesis seeks to answer the overarching question: How can development of advanced models and control enable cost-effective PtH2 solutions facilitating the integration of renewable energy sources in complex energy systems? This question is further addressed through in-depth investigations of four specific research questions: (i) How can PtH2 models be developed to holistically embody the full sense of multiscale and multi-physical attributes, meeting model requirements for their control purposes in RENSs? (ii) How can the synergy between PtH2 systems and other assets within renewable hydrogen hubs be optimized to ensure system stability in the presence of fluctuating renewables and grid disturbances? (iii) How can cross-sectoral energy management of PtH2 systems be strategically optimized to maximize their added value? (iv) How can the potential grid frequency services of PtH2 systems be efficiently quantified, harnessed and strategically aggregated to ensure a stable system frequency while minimizing operational costs? After the introduction given in Chapter 1, an integrated modeling framework for Pt

Line-commutated converter based high voltage direct current (LCC-HVDC) has been applied for transferring bulk power from wind farms to load center through long distance in many countries. When the blocking fault of LCC-HVDC system occurs, the surplus reactive power accumulated at the sending end will lead to an overvoltage thus causing the disconnection of wind turbines. To maintain the reliable connection of wind turbines and ensure the stability of power system, this paper introduce one superconducting magnetic energy storage (SMES) unit to connect in parallel with the rotor side of doubly fed induction generator (DFIG). By controlling the energy side converter and rotor side converter to inject demagnetizing current and reactive current into the rotor, the proposed scheme can effectively stabilize key parameters of wind turbine and provide desirable reactive power support, showing a favorable high voltage ride through (HVRT) performance. Several cases based on PSCAD/EMTDC & MATLAB/Simulink co-simulation together with economic analysis are conducted to demonstrate the feasibility and superiority of the proposed scheme on enhancing HVRT capability of DFIG-based wind farms.