To address the source-load power mismatch in off-grid photovoltaic (PV) hydrogen production systems arising from PV power fluctuation and the slow dynamics of alkaline water electrolyzers

a multi-mode coordinated control strategy based on real-time power comparison and multi-loop coordination is proposed. Firstly

the mathematical models of the PV array

a three-phase interleaved Buck converter

and the alkaline water electrolyzer are established. Then

a mode decision mechanism is designed to continuously compare the estimated maximum PV power with the temperature-adaptive safe power limit of the electrolyzer

thereby integrating electrolyzer thermal dynamics into the control loop for adaptive safety boundary adjustment. Furthermore

a power-voltage cascade controller is constructed to achieve smooth transitions between the maximum power point tracking (MPPT) and power-limiting modes

with a power overshoot of 1.48% and a mode-switching dead time of 0.3 s. Meanwhile

a current protection loop and a low-selector are introduced

suppressing the current overshoot from 14.8% to 4.96% under degraded main-loop performance. Simulation results demonstrate that under various disturbances

including irradiance variations and electrolyzer temperature rise

the proposed strategy effectively maintains source-load power balance

and ensures equipment safety

and achieves stable mode switching.