Reliable condition monitoring of electrolysers and fuel cell systems is becoming increasingly important in the context of dynamic operating strategies. Traditional methods such as electrochemical impedance spectroscopy (EIS) provide detailed information about linear processes, but are only suitable to a limited extent for continuous online operation under load.
A technical note has now been published on harmonic ratio analysis (HRA), which describes a nonlinear, online-capable diagnostic method. The method uses targeted periodic modulation of the operating point and evaluates the harmonic component of the voltage response using Fourier analysis. By selectively considering individual harmonic ratios, symmetrical and asymmetrical nonlinearities can be distinguished—for example, transport-related effects, water balance disturbances, or kinetic changes.
The publication describes:
- the physical principle of HRA
- diagnostic indices based on harmonic ratios
- a reproducible measurement protocol
- quality criteria for robust online applications
- classification in relation to EIS and global distortion parameters
The aim of the work is to provide a methodologically clearly defined framework for the implementation of harmonic-based online diagnostics in test benches, stack controllers, and industrial monitoring systems.
The technical note is aimed at developers, research groups, and system integrators in the fields of water electrolysis, fuel cell technology, and electrochemical energy systems.
The complete publication is available via the following link:
https://zenodo.org/records/18743943
