A Novel System for Measuring Alternating Current Impedance Spectra of Series-Connected Lithium-Ion Batteries With a High-Power Dual Active Bridge Converter and Distributed Sampling Units

Alternating current (ac) impedance spectra facilitate lithium-ion battery management. Realizing a low-cost and low-complexity onboard impedance measuring system is a vital issue for the management based on the ac impedance. In the article, a novel impedance measuring system combined with a high-power dual active bridge (DAB) converter and distributed sampling units is proposed and verified. The DAB converter is designed to generate the ac disturbance to ensure a quasi-steady measurement of the battery impedance. The distributed signal sampling units simultaneously measure the voltage and current of all the series-connected battery cells in a module to measure their impedance. The measured impedance in a frequency range of 0.1-500 Hz shows the feasibility of the system. The root-mean-square errors of the measured impedance phase from 0.2 to 200 Hz and the magnitude from 0.1 to 500 Hz are less than 6.9% and 4.0%, respectively. The errors in some frequency ranges are slightly larger, which are analyzed. The novelty is reflected in that the system is easily integrated into a bidirectional onboard charger and compatible with the battery management system, thus reducing costs and complexity. It provides a basis for the onboard application of the battery impedance.