Abstract: This paper analyzes the inefficiency mechanism of low-load alkaline water electrolyzers（AWEs）. It is found that through modifying the excitation electric field, the low-load performance of AWEs can be greatly enhanced. Based on this, a multi-modal selfoptimization（MMSO） control strategy and the corresponding prototype converter are proposed. The effectiveness of the proposed method is verified by a 2 Nm3/h AWE（about 10 kW） directly driven by PV arrays. Experimental results show that compared to the conventional DC power supply, 1) the maximum efficiency improvement can exceed two times, 2) under the constraint of efficiency≥50%, the system operation is enhanced from 30%-100% to 10%-100% of rated load; 3) the AWE can follow the fluctuating PV power well.