Abstract
Impedance spectroscopy can characterise a variety of states within a battery and shows great potential for application in safety warning and condition assessment, but there is a lack of an effective online monitoring method. Therefore, this paper proposes a method for online measurement of impedance spectroscopy based on harmonic injection of equalization currents, which superimposes different frequency sinusoidal perturbation signals on the original equalization currents through process reconstruction and collaborative control, and realises real-time impedance spectroscopy monitoring at the level of single-cell without additional hardware. In order to verify the validity of the method proposed in this paper, a hardware experimental platform was constructed. Firstly, a four-switch Buck-Boost (FSBB) converter is used to perform energy equalization of a six-cell Li-ion battery pack under different working conditions, and the experimental results show that the Li-ion battery pack can be Equalized by the active equalization circuit under the states of resting, charging and discharging in about 60 minutes, 75 minutes and 100 minutes respectively.Then, the impedance spectroscopy in the frequency range of 0.2 Hz to 800 Hz is achieved through the collaborative control of active equalization and impedance spectroscopy. Finally, in order to verify the reliability of the measured data, the measured impedance spectroscopy data were evaluated by the Kramers-Kronig (K-K) transforms, and the data measured at the initial stage were compared and analyzed with the data measured by a professional electrochemical workstation, which verified the validity of the method proposed in this paper.
