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Impedance spectroscopy for battery monitoring with switched mode amplifiers

Impedance Spectroscopy is a well-known measurement technique for electrochemical systems, such as a battery half-cell. Once this method would be implemented in the battery management system and performed online during operation it could provide a monitoring system for the whole pack and increase its lifetime and safe operation. Current solutions are either inaccurate or too big, expensive and energy inefficient. The presented approach proposes a dual use of the battery charger which incorporates a switched mode amplifier to generate the stimuli current necessary to perform an Impedance Spectroscopy. The drawback of this method are the distortions associated with the modulation of the measurement frequency onto a carrier frequency. The influence of the DC-link voltage and the switching frequency on the on the total harmonic distortion are analysed. These theoretical results are compared with the ones from experiments. A custom designed switched amplifier was built up, specifically designed for performing Impedance Spectroscopy on a battery pack. This technology could allow impedance monitoring of every cell in the battery pack and make a better estimation of the state of the battery possible.