Dynamic Impedance Modeling of an Alkaline Electrolyzer – A Practical Approach

Power supplies for water electrolysis comprise various electrical topologies and power qualities. The increasing urgency to produce hydrogen at scale underlines the need to examine the interaction between the rectifier supplying DC current, and the electrolytic stack producing hydrogen and oxygen. Rectifier-electrolyzer interactions can be analyzed in detail by describing the electrolytic stack as an equivalent electric circuit. Therefore, this work introduces a practical approach to build equivalent circuit models for commercial electrolyzer systems powered with industrial rectifiers. For this purpose, an equivalent electric circuit with minimum number of elements is used to model the complex impedance in the frequency domain relevant to the rectifiers of interest. Electrochemical impedance spectroscopy is performed at the electrolyzer stack level for a broad range of applied voltages, allowing to parametrize the MATLAB/Simscape model. The model provides an accurate representation of the electrolyzer’s dynamic response to rectifier waveforms showing different degrees of ripple.