Excitation Current Generation Circuit for Electrochemical Impedance Spectroscopy Measurement Based on a Variable-Inductance Bidirectional Ćuk Converter for Wideband AC Excitation

Lithium-ion batteries have become essential for electric vehicles and energy storage systems; however, safety risks related to thermal runaway have emerged as a critical concern. Conventional monitoring methods based on voltage, current, and temperature cannot detect internal faults at an early stage. To address this limitation, proactive diagnostic methods employing electrochemical impedance spectroscopy (EIS) have been extensively investigated. This study presents an excitation-current generation method for EIS measurement based on a variable-inductance bidirectional Ćuk converter. The proposed circuit operates using the energy stored in the battery system, eliminating the need for an external auxiliary power source for excitation energy, while generating sinusoidal excitation currents over a wide frequency range. A small-signal analysis incorporating a first-order battery equivalent circuit model and the parasitic elements of the Ćuk converter was conducted to evaluate system stability and the effects of key design parameters. The experimental results confirm sinusoidal excitation-current generation over the frequency range of 0.1 Hz to 3 kHz. Under a representative test condition, the prototype generates a sinusoidal excitation current with a 2 A peak-to-peak AC component superimposed on a 3 A DC component. These findings verify the feasibility of the proposed method as a dedicated excitation-current generator for embedded EIS measurements.