Online Internal Temperature Estimation for Lithium-Ion Batteries Using the Suppressed Second-Harmonic Current in Single- Phase DC/AC Converters

Online monitoring of Lithium-ion batteries (LIBs) internal temperature (IT) is a mandatory requirement to ensure their safety and longevity. In this article, the second-harmonic current (SHC) that inherently exists in single-phase dc/ac converters is utilized to estimate LIB IT for the first time. First, the SHC needs to be suppressed to the appropriate level as a disturbance signal for online impedance measurement. Then, the dual-channel digital lock-in amplifier is used to calculate LIBs impedance at the second-harmonic frequency (SHF). Moreover, the Pisarenko harmonic decomposition algorithm is adopted to estimate the actual SHF to ensure the accuracy of the impedance calculation. Three commercial 18 650 LIBs are tested at the experimental setup. A strong correlation between the imaginary impedance at SHF and IT is observed, which is nearly not affected by the battery's state of charge. Therefore, an online SHF impedance-based battery IT estimation method is developed. Finally, the validity of the proposed method is confirmed through a comparison between actual and online estimated temperatures.