Online Broadband Battery Impedance Spectroscopy Using Current-Mode Boost Converter

In this article, an online method of broadband battery impedance spectroscopy is proposed, in which the excitation signal is injected through the inner feedback loop of a dc/dc boost converter with average current-mode control (ACMC). By deriving the average state-space model of the conventional boost converter, it is shown that an open-loop converter exhibits a resonant frequency response in regard to the injected signal, whereas the compensated current loop in ACMC produces a controllable, flat-gain closed-loop transfer function that allows broadband current excitation signals to be injected into the battery without the distortion that is seen in the open-loop configuration. In the presented method, the converter is set to discharge the battery at a constant C-rate during impedance measurement, while a broadband signal is superimposed onto the loop reference current. A low-dropout (LDO) regulator is then used to filter out disturbances caused in the converter output. The proposed approach is experimentally implemented, and a discrete-interval binary sequence (DIBS) signal is utilized to measure the impedance of two 18650 lithium-ion batteries in several arbitrary frequencies at once in the 0.1 Hz-1 kHz range. The measured spectra are validated by a commercial impedance analyzer.