A two-stage real-time equalization control strategy for off-grid multi-electrolyzer systems considering electrolyzer degradation

Renewable-powered off-grid hydrogen production can generate zero‑carbon hydrogen, but intermittent output causes uneven operation among multiple alkaline electrolyzers (AELs) and accelerates AEL degradation. This paper proposes a two-stage real-time equalization control strategy to balance operational differences among AELs. The control process consists of startup and shutdown stages, triggered in real time according to AEL states and renewable output. In the startup stage, non-production AELs with fewer switch actions are started first, with the standby AELs given the highest priority to equalize differences in switch actions. In the shutdown stage, AELs with longer operating times are shut down first, thereby equalizing differences in operating time. We also adopt a refined AEL model that accounts for state transitions and voltage degradation. Case studies compare the proposed strategy with simple start-stop, cycle rotation, and multi-objective weighted rolling control strategies. Simulation results demonstrate that the proposed strategy is superior for long-term control: it effectively balances operational differences and degradation among AELs, reducing the standard deviation of AEL cluster degradation by 99.3%, 93.5%, and 94.6%, respectively, compared with the three benchmark methods. It also avoids the strong sensitivity of rotation cycle-based strategies to the rotation cycle length, further confirming its effectiveness and superiority.