The Phase-locked loop (PLL) is widely used to synchronize the converters with the grid. However, the asymmetric dynamic characteristics of the PLL may cause frequency coupling effects and even cause sub/super synchronous oscillation in weak grids. This paper analyzes the frequency coupling effects of the conventional dual second-order generalized integrator (DSOGI) PLL. A novel PLL structure is proposed to eliminate the frequency-coupling effects, simultaneously controlling the d-axis and q-axis voltage components. The inter-harmonic components can be suppressed, and the perturbation propagation paths through the PLL can be prevented. In this way, the synchronization stability of converters under weak grids is improved. Also, the design procedure of the structure and parameters of the PLL are provided. Finally, the simulations and experimental results verify the effectiveness of the proposed solution.

Electrolyzers are widely used in renewable energy hydrogen production, and the performance of electrolyzers is directly related to dc–dc converters. To realize the high-efficiency operation of the electrolyzer, new challenges, such as a high step-down ratio and low output current ripple, are put forward for the dc–dc converter. In this article, we propose a novel type of dc–dc converter for hydrogen production. The topology is simple and has the advantages of higher step-down gain and low switching stress. In addition, the scheme can achieve ultralow output current ripple without active devices. Finally, the topology connects the electrolyzer hydrogen production load in the experiment to verify the scheme's effectiveness.

Green hydrogen is one of the most promising choices among hydrogen production methods due to its zero-emission, environmentally friendly, and sustainable characteristics. Choosing an appropriate model for green hydrogen production via photovoltaic electrolysis is critical to improving its efficiency and reliability. However, existing studies lack a comprehensive review and comparison of photovoltaic electrolysis for green hydrogen production. This gap makes it challenging for researchers to select suitable models for photovoltaic electrolysis in their investigations. To address this challenge, this article provides a comprehensive review and comparison of existing modeling research on photovoltaic hydrogen production systems. It classifies and analyzes photovoltaic panels, converters, and electrolyzers in photovoltaic electrolysis hydrogen production, summarizing general modeling approaches and criteria for selecting appropriate electrolyzer models for different applications. The article also highlights shortcomings in existing research and proposes directions for future investigations.