Cell temperature and degradation measurement in lithium ion battery systems using cell voltage and pack current measurement and the relation of cell impedance to temperature based on signal given by the power inverter

摘要

A method and system for determining the temperature of cells in a battery pack, without using temperature sensors, by measuring the impedance of the cells and using the impedance to determine the temperature. An AC voltage signal is applied to the battery pack, and a time sample of voltage and current data is obtained. The voltage and current data is narrowed down to a simultaneous time window of interest, and a fast fourier transformation is performed on the windowed voltage and current data to identify voltage and current magnitudes at one or more specific frequencies. The voltage and current magnitudes are used to determine the impedance at the one or more frequencies. Finally, the impedance is used to determine the temperature of the cell or cells using a look-up table, where the impedance, the frequency, and a state of charge are used as input parameters for the look-up.

主权项

1. A temperature measurement system for cells in a battery pack, said temperature measurement system comprising:
means for applying an alternating current (AC) voltage signal to the battery pack; a voltage sensor for measuring a voltage across a cell group in the battery pack, where the cell group is comprised of one or more cells in parallel, said voltage sensor providing a voltage signal for the cell group; a current sensor for measuring a battery pack current, said current sensor providing a current signal for the battery pack; and a battery pack controller in communication with the voltage sensor and the current sensor, said controller including a processor and memory, where the controller is configured with; a windowing module which receives the voltage signal and the current signal and reduces the signals to a simultaneous time window; a fast fourier transformation (FFT) module which performs an FFT on the voltage signal and the current signal for the time window to provide voltage and current amplitudes at one or more frequencies; and a computation module which computes an impedance for the cell group from the voltage amplitude and the current amplitude at a chosen frequency, and uses the impedance and the chosen frequency, along with a state of charge value, to determine the temperature of the cell group.