Fast Approach for Battery Impedance Identification Using Pseudo-Random Sequence Signals

Online measurements of the battery impedance provides valuable information on the battery state-of-charge and state-of-health which can be utilized for improving the safety and the performance of the associated system. The electrochemical-impedance- spectroscopy (EIS) is widely used for battery impedance measurements but it is not the most applicable solution for online measurements due to its slowness and complexity. These drawbacks can be improved using broadband signals, such as, pseudo-random-sequences (PRS), which are fast and easily implementable. However, the non- linear behavior of batteries have significant effect on the impedance measurements and the selection of the PRS signal. Majority of the PRS signals are applicable for measurements of linear systems but also signals for non-linear system identification do exist. Moreover, the reduced accuracy and signal-to-noise ratio of the PRS signals compared to the EIS make the filtering of the results as well as the amplitude design important aspects. This paper demonstrates the use of two PRS signals, the pseudo-random-binary-sequence (PRBS) and a ternary- sequence with better toleration to battery non-linear effects, with comprehensive amplitude and filtering design for battery impedance measurements. The results are referenced and validated to practical EIS measurements in various operating conditions for lithium-iron-phosphate cell.