Discrete Pulse Control Strategy for Embedded Li-ion Batteries Broadband EIS Measurement System

Electrochemical impedance spectroscopy (EIS) of lithium-ion (Li-ion) batteries provides comprehensive information on material properties, interfacial phenomena, and electrochemical reactions. An embedded EIS measurement system, based on the power interface dc-dc converter of Li-ion battery, can achieve nondestructive, low-cost, and accurate online EIS measurement. Therefore, it holds great potential for real-time status assessment and early fault detection of Li-ion batteries. However, accurately measuring EIS at high frequencies poses a challenge due to the limited bandwidth of dc-dc converter's controller. To address this issue, a discrete pulse (DP) control is proposed in this letter. The proposed DP control regulates constant current charging current by generating two discrete duty ratios and achieves real-time EIS measurement by introducing a disturbance duty ratio to fit ac disturbance signal. Therefore, the implementation of DP control eliminates the need for proportional-integral (PI) regulator and overcomes the limitation of controller bandwidth on the frequency range of ac disturbance signal. Experimental results show that DP control achieves accurate EIS measurement from 0.1 to 25 kHz, with a maximum normalized root mean square error of only 1.61% (75.93% less than PI control), and significantly reduces measurement time to 59.20 s (86.79% less than commercial electrochemical workstation).