Flexible quadratic residue ternary excitation for lithium-ion battery broadband impedance measurement

Broadband impedance is a powerful tool for state estimation and fault diagnosis in lithium-ion batteries (LIBs). However, due to the complex electrochemical kinetics, characteristic impedance features are often spread across a wide frequency range. To address this, we propose a broadband impedance measurement framework that enables flexible frequency range adjustment with reduced measurement time and minimal nonlinear distortion. A simplified quadratic residue ternary signal (SQRTS) is designed as the excitation input, incorporating a single zero bit at the end to optimize the sequence structure. The SQRTS supports adjustable sequence lengths to minimize the injection period and suppress nonlinear effects. In addition, an adaptive window filter is developed to accurately extract impedance responses across different frequency bands. Experimental results demonstrate that the proposed method achieves high accuracy and robustness while reducing the signal injection time by approximately 49.9 % compared to the conventional maximum-length binary sequence (MLBS).