Fast Measurement Method for Lithium-Ion Battery EIS Based on Three-Level Excitation

Conventional sinusoidal sweep methods are time-consuming, especially in the low-frequency region, which limits their application in rapid and online battery condition monitoring. Moreover, under practical operating conditions, low-frequency drift, operating disturbances and limited observation windows further deteriorate impedance extraction accuracy. This paper proposes a rapid wide-band impedance measurement method for lithium-ion batteries based on three-level excitation. First, a three-segment three-level excitation strategy was developed by performing frequency-band partitioning, target frequency point configuration, and discrete frequency grid matching, enabling efficient frequency-domain resource allocation within a limited test duration. To improve the reliability of impedance estimation under operating disturbances, a low-order drift model and a multi-window redundant observation framework were established to decouple the impedance response from slowly varying drift components. Furthermore, a residual compensation method combining physical constraints with a Shallow Recurrent Decoder-based Reduced Order Model (SHRED-ROM) is proposed to correct low-frequency residual errors. Experimental results demonstrate that the proposed method can acquire a broadband impedance spectrum over 0.01 Hz–1 kHz within 179 s, achieving RMSE values of 0.436 mΩ and 0.474 mΩ for the full frequency band and low-frequency region, respectively. Under equivalent constant-voltage charging conditions, the proposed method reduces the impedance magnitude error at 0.01 Hz from 48.59 mΩ to 3.43 mΩ and decreases the phase error from 23.95° to 7.09° compared with the multi-sine excitation method. The proposed method also maintains high measurement accuracy under operating disturbances, demonstrating improved robustness for low-frequency impedance acquisition. These results indicate that the proposed approach provides an effective solution for rapid broadband EIS measurement and online condition monitoring of lithium-ion batteries.