Influence of rectifiers on the energy demand and gas quality of alkaline electrolysis systems in dynamic operation

摘要

This paper investigates the correlation between different rectifier topologies and the energy demand as well as the gas quality of an alkaline electrolysis. The focus lies on recent scenarios which require partial load operation of electrolyzers. The layout-dependent current outputs of three conventional and a self-developed rectifier were simulated based on actual measurement data. After the down-scaling of the acquired current profiles, these were applied to a lab-scale alkaline electrolyzer. The rectifier structures are assessed for dynamic operation between 25% and 100% of their nominal load. Experimental results show a strong influence of the rectified current quality on the required electrical energy of the electrolysis process. Conventional thyristor structures with a high current ripple consume up to 13% more energy compared to the newly designed process current source, which provides an almost perfectly smoothed direct current. Additionally, high current ripples, which occur especially in low load scenarios, cause oxygen to diffuse to the hydrogen half cell and reduce the product gas purity. Therefore, not every rectifier is suited for dynamic operation of electrolysis systems.