Rapid impedance measurement using chirp signals for electrochemical system analysis

Energy storage (batteries) and conversion devices (fuel cells) operate based on electrochemical principles. Electrochemical impedance spectroscopy (EIS) is an important experimental technique that can be used to optimize the performance of these devices at the design stage. Further, EIS can also be used for non-invasive, in-situ diagnostics of device performance, while operational. While EIS is a powerful technique, the instrumentation required for implementation can be bulky and the time for analysis could also become unacceptable, particularly for online applications. The proposed work is an investigation and development of a rapid impedance measurement technology using large bandwidth and short duration diagnostic signals. The key concept behind the approach is the use of a particular definition of instantaneous frequency in tandem with chirp signals for testing. The instantaneous frequency definition allows one-to-one time frequency mapping and the chirp signal incorporates a wide bandwidth of frequencies. As a result, a novel impedance plot qualitatively, and largely quantitatively, matching the corresponding EIS plot is generated. Consequently, any diagnostic approach based on EIS can potentially be realized using the proposed approach. The impedance plots are generated in a very short time making the approach amenable for online applications. In-silico validation of the proposed method on few equivalent circuits of electrochemical systems is presented in this work; future work will include experimental validation of the technique on real electrochemical systems.