SOC estimation method based on the ultrasonic guided waves considering the significant effect of charge/discharge rate

Estimating the state of charge (SOC) for lithium-ion batteries is one of the crucial issues for energy storage devices. To improve the accuracy and efficiency of the predictions, on the one hand, the researchers continuously develop more advanced algorithms based on the signals of temperature, voltage and current; on the other hand, new types of sensors are also adopted to assist in predictions. Evidence has shown that ultrasonic guided waves are highly related to the SOC, and it is now regarded as one possible signal to help predict the SOC. However, the existing literatures often ignored the effect of charge/discharge rates on ultrasonic guided waves. To bridge this gap, this study quantified the effect of the charge/discharge rates to improve the accuracy of the SOC estimation method based on ultrasonic guided waves. First, the experiments on measuring the ultrasonic guided waves in battery considering temperature, SOC and charge/discharge rates are conducted systematically, where the time of flight (TOF) signal is proposed as a feature for analysis. The temperature compensation method is established to study the effect of the charge/discharge rates. Second, the mechanisms of the TOF change in dynamic charge/discharge are analyzed after temperature effect compensation. Finally, the SOC prediction method based on the ultrasonic guided waves considering the rate with temperature and rate mutation compensation is established. The results make it possible for real-time and accurate monitoring of battery SOC by ultrasonic guided waves.