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Alkaline water electrolysis is one of the most promising solutions for large-scale hydrogen production from renewable energy sources (RESs) due to its low cost and maturity. However, the low-load performance of alkaline water electrolyzers (AWEs) is poor, which makes it difficult to follow fluctuant RESs in wide operating range. To address this problem, a novel equivalent circuit model of industrial AWESs is established based on its internal structure and operating principle. Then, a multimodal self-optimization control method and its prototype electrolysis converter are proposed to improve the efficiency of hydrogen production in low load. Compared with traditional methods, the proposed method can provide stable pulse current for the electrolyzer to realize efficiency improvement in low load. Finally, based on a 10 KW AWEs experimental platform, the correctness of the theoretical analysis is verified. The experimental results show that the proposed control strategy has a significant effect on the efficiency improvement of the 10 KW AWEs in low load.

Hydrogen production from photovoltaic arrays is a promising way to fully utilize the solar energy and to relieve consumption pressure of the power system. The low-cost and mature alkaline water electrolysis is suitable for large-scale hydrogen production. However, the low-load inefficiency of alkaline water electrolyzers greatly limits their operation range (usually 40%–100% of rated load). Hence, alkaline water electrolyzers are hard to follow the fluctuating photovoltaic power in full range. Focusing on this problem, this article analyzes the inefficiency mechanism of low-load alkaline water electrolyzers. It is found that through modifying the excitation electric field, the low-load performance of alkaline water electrolyzers can be greatly enhanced. Based on this, an optimal current pulsewidth modulation control strategy and the corresponding prototype converter are proposed to regulate alkaline water electrolyzers directly driven by photovoltaic arrays. The effectiveness of the proposed method is verified by a 2 Nm3/h commercial alkaline water electrolyzer. Experimental results show that compared to the conventional dc power supply, 1) the maximum efficiency improvement can exceed two times, and 2) the alkaline water electrolyzer can follow the fluctuating photovoltaic power well.