Abstract
In this paper, a method for monitoring SoC of a lithium-ion battery cell through continuous impedance measurement during cell operation is introduced. A multi-sine signal is applied to the cell operating current, and the cell SoH and SoC can be simultaneously monitored via impedance at each frequency. Unlike existing studies in which cell impedance measurement is performed ex situ through EIS equipment, cell state estimation is performed in situ. The measured impedance takes into account cell temperature and cell SoH, enabling accurate SoC estimation. The measurement system configured for the experiment and considerations for the selection of measurement parameters are described, and the accuracy of cell SoC estimation is presented.
Highlights
A Li-ion battery is a type of secondary battery in which lithium ions move from a negative electrode to a positive electrode through an electrolyte during a discharge process
A multi-sine signal is applied to the cell operating current, and the cell state of health (SoH) and state of charge (SoC) can be simultaneously monitored via impedance at each frequency
The end of life (EoL) of a battery is reached when the energy content or power capacity is no longer sufficient for the application. This can vary depending on battery application; there is no universal definition of how many cell SoHs have reached EoL
Summary
A Li-ion battery is a type of secondary battery in which lithium ions move from a negative electrode to a positive electrode through an electrolyte during a discharge process. Errors in voltage, current, and temperature measurements contribute to increasing the estimation error These errors are more integrated and intensified as battery cell operating time increases. This paper does not deal with the method of estimating the cell SoH and SoC from the measured impedance. To estimate the cell state, a multi-sine signal with a small amplitude is applied to the cell operating current, and the cell impedance is measured through the amplitude of the voltage response. In the proposed battery SoC monitoring method, the sum signal of two test frequencies is excited to the cell operating current and its response voltage is measured. The impedance at each test frequency is obtained by substituting the amplitude of each response voltage into Equation (3)
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