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

• US 8,994,340 B2
• Filed: 05/15/2012
• Issued: 03/31/2015
• Est. Priority Date: 05/15/2012
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Matthe, Roland, Humbert, Hans-Joachim, Kowalczyk, Konrad
• Primary Examiner(s): Kik, Phallaka
• Application Number:
  US13/471,803
• Publication Number:
  US 20130307487A1
• Time in Patent Office: 1,050 Days
• Field of Search: 320/153, 320/104, 320/112, 320/126, 320/134, 320/136, 320/144, 320/159, 320/152, 320/162, 307/150
• US Class Current: 320/153
• CPC Class Codes: G01K 2007/166 Electrical time domain reflectometry
• CPC Class Codes: G01K 2217/00 Temperature measurement using electric or magnetic components already present in the system to be measured
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: G05F 3/02 Regulating voltage or current
• CPC Class Codes: H01M 10/486 for measuring temperature
• CPC Class Codes: H01M 2220/20 Batteries in motive systems, e.g. vehicle, ship, plane
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

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.

Claims

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.

2. The temperature measurement system of claim 1 wherein the impedance is measured and used to determine the temperature of each cell group in the battery pack.

3. The temperature measurement system of claim 1 wherein the battery pack is used in an electric or hybrid-electric vehicle.

4. The temperature measurement system of claim 3 wherein the means for applying an AC voltage signal includes a traction inverter which provides power to a drive motor.

5. The temperature measurement system of claim 4 wherein the AC voltage signal occurs naturally as a result of the traction inverter powering the drive motor.

6. The temperature measurement system of claim 4 wherein the AC voltage signal is artificially generated specifically for the purpose of impedance measurement.

7. The temperature measurement system of claim 1 wherein the battery pack controller uses the temperature of the cell group to assess performance and state of health of the cell group.

8. The temperature measurement system of claim 1 wherein the computation module uses a look-up table to determine the temperature of the cell group based on the impedance, the chosen frequency and the state of charge.

9. A battery pack system for an electric vehicle including impedance-based temperature measurement, said battery pack system comprising:

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; 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 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.

10. The battery pack system of claim 9 wherein the AC voltage signal occurs naturally as a result of the traction inverter powering the drive motor.

11. The battery pack system of claim 9 wherein the AC voltage signal is artificially generated specifically for the purpose of impedance measurement.

12. A method for determining the temperature of cells in a battery pack, said method comprising:

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, using a processor, 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, using the processor, an impedance for the cell group from the voltage amplitude and the current amplitude at a chosen frequency; and

determining, using the processor, the temperature of the cell group based on the impedance and the chosen frequency, along with a state of charge value.

13. The method of claim 12 wherein the battery pack is used in an electric or hybrid-electric vehicle.

14. The method of claim 13 wherein the AC voltage signal is provided by a traction inverter which provides power to a drive motor.

15. The method of claim 14 wherein the AC voltage signal occurs naturally as a result of the traction inverter powering the drive motor.

16. The method of claim 14 wherein the AC voltage signal is artificially generated specifically for the purpose of impedance measurement.

17. The method of claim 12 further comprising using the temperature of the cell group to assess performance and state of health of the cell group.