Fast Lithium-ion Battery Broadband Impedance Identification with Enhanced Mid-to-low Frequency

Pseudorandom sequence (PRS) offers a rapid impedance measurement solution for lithium-ion batteries. However, PRS suffers from limited accuracy in the mid-to-low frequency range due to the low power content and sparse distribution of harmonics. Motivated by this, a parallel quadratic residue ternary signal with an almost theoretical minimum measurement time is proposed. By enhancing the power in mid-to-low frequency band, the first few low-frequency impedance points can be accurately obtained without any additional filters. Moreover, a two-stage filter with an iterative procedure is introduced, which eliminates outliers using a predefined threshold and obtains the filtered impedance through Fourier series fitting. Experimental validation proves that the proposed method achieves a max normalized root means square error of 0.59% and max absolute residual of 0.48% under various states of charge, states of health and temperatures, confirming its effectiveness for impedance measurement.