Wide-range operating control of alkaline electrolyzer for off-grid renewable hydrogen production

Hydrogen production from renewable generation via water electrolysis is one of the key methods to deal with the increasing penetration of renewables into power systems. However, technically mature alkaline water electrolyzers (AWEs) struggle to track widely fluctuating renewable power outputs due to thermodynamic delays in their dynamic processes and safety constraints arising from frequent operating mode changes. To exploit the operating range of AWEs while respecting thermodynamic behavior and safety limits, this paper develops an accurate electro-thermal-hydrogen dynamic coupling model for an AWE system by incorporating a pair of time-delay constants, based on which an adaptive nonlinear model predictive control (ANMPC) strategy is proposed to manage the rise in hydrogen-to-oxygen level caused by pressure fluctuations under low-load conditions, compensate for time-delay responses under low- and high-temperature conditions, and enable flexible multi-mode switch under overload conditions. The proposed ANMPC strategy is tested based on a hardware-in-the-loop platform, validating its effectiveness in wide-range load adjustment and multimodal switch under highly dynamic conditions.