Online Temperature Estimation for Lithium-Ion Batteries Utilizing a Single-Frequency Impedance Unaffected by Their Peripheral Circuits

Online temperature monitoring is important for ensuring safe operation of lithium-ion batteries (LIBs). As the battery impedance is related to the internal physical and chemical processes, some efforts have been made to realize sensor-less temperature estimation based on the impedance characteristics of LIBs. Unfortunately, the existing impedance-based temperature estimation models are usually derived from pure battery cells, and the effect of peripheral circuit components of systems (e.g., resistors and capacitors) on measured impedance has not been considered. To fill the gap, this paper investigates the effect of peripheral circuits (including filter circuits, balancing circuits, and line resistance) on the measured impedances. Taking a ternary lithium battery as a case study, it is found that the imaginary-part impedance at the frequency band of 100 Hz–1 kHz is almost not affected by the peripheral circuits. This can indicate the temperature variation of batteries, and it is independent of state of charge (SoC) and state of health (SoH), which can be chosen as a thermal sensitive electric parameter (TSEP) of batteries. A similar conclusion can also be drawn for a battery with different types and packaging. Based on the obtained TSEP, a single-frequency impedance-based temperature estimation method is presented. Taking a dc/dc converter as a case study, experimental results demonstrate that the estimation method can be integrated into an interface converter for batteries, and the maximum estimation error is less than 5°C.