Broadband electrochemical impedance spectroscopy of lithium-ion batteries based on a current-controlled DC–DC converter for energy storage systems

Electrochemical impedance spectroscopy (EIS) is a nondestructive technique for battery state monitoring in energy storage applications. Accurate broadband online EIS of large-capacity lithium-ion batteries under varying state-of-charge (SOC) conditions remains challenging because converter-based methods suffer from limited control bandwidth and frequency-dependent battery terminal current distortion caused by the output filter and battery branch. To address this issue, this work develops a terminal current control strategy for a DC–DC converter by modeling and compensating current transmission from the converter-side inductor to the battery terminal. The inner loop adopts mixed-signal hysteretic current control (MSHCC) as an inductor current excitation unit with high bandwidth, while large-signal and small-signal models quantify the effects of parasitic resistance, equivalent delay, SOC-dependent operating point variation, and filter current division. A modified cascaded second-order generalized integrator proportional-integral (SOGI-PI) outer loop extracts the dc component and ac amplitude of the terminal current and performs amplitude envelope compensation. Experiments show that the method regulates the battery terminal ac perturbation at 5 A while maintaining a dc charging current of 10 A from 0.1 Hz to 50 kHz. At SOC levels of 10%, 50%, and 90%, the EIS measurements exhibit NRMSEs ranging from 1.54% to 1.94%, while the measurement time is reduced from 452 s to 218 s the commercial electrochemical workstation. These results demonstrate the feasibility of terminal current regulated converter-based online EIS for embedded broadband impedance measurement and state monitoring of lithium-ion batteries in practical energy storage systems.