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
First Claim
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;
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.
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Accused Products
Abstract
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.
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Citations
20 Claims
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1. A temperature measurement system for cells in a battery pack, said temperature measurement system comprising:
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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; 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A battery pack system for an electric vehicle including impedance-based temperature measurement, said battery pack system comprising:
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a battery pack containing a plurality of cell groups, where each cell group is comprised of one or more cells in parallel; a traction inverter for providing power to a drive motor, said traction inverter also applying an alternating current (AC) voltage signal to the battery pack; a plurality of voltage sensors for measuring a voltage across each of the cell groups in the battery pack, said voltage sensors providing a voltage signal for each of the cell groups; a current sensor for measuring a battery pack current, said current sensor providing a current signal for the battery pack; a windowing module which receives the voltage signals 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 signals 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 each of the cell groups from the voltage amplitudes 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. - View Dependent Claims (11, 12, 13)
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14. A method for determining the temperature of cells in a battery pack, said method comprising:
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applying an alternating current (AC) voltage signal to the battery pack; measuring a voltage across a cell group in the battery pack and providing a voltage signal for the cell group, where the cell group is comprised of one or more cells in parallel; measuring a battery pack current and providing a current signal for the battery pack; reducing the voltage signal and the current signal to a simultaneous time window; performing a fast fourier transformation (FFT) on the voltage signal and the current signal for the time window to provide voltage and current amplitudes at one or more frequencies; computing an impedance for the cell group from the voltage amplitude and the current amplitude at a chosen frequency; and using the impedance and the chosen frequency, along with a state of charge value, to determine the temperature of the cell group. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification