Method and control device for impedance-based determination of a state of charge of at least one battery cell and motor vehicle

Patent metadata

Field	Value
Publication number	US-11604227-B2
Application number	US-202117496144-A
Country	US
Kind code	B2
Filing date	Oct 7, 2021
Priority date	Oct 15, 2020
Publication date	Mar 14, 2023
Grant date	Mar 14, 2023

Abstract

A method for determining a state of charge of at least one battery cell, having the following steps to enable an improved determination of the state of charge of a lithium iron phosphate cell: generating an alternating current pulse in a circuit connected to the at least one battery cell, determining an impedance of the at least one battery cell on the basis of the alternating current pulse and determining the state of charge by comparing the impedance to predefined map data, wherein a relationship between the impedance and the state of charge of the at least one battery cell is determined from the predefined map data.

First claim

The invention claimed is:

1. A method for determining a state of charge of at least one battery cell, comprising:
generating an alternating current pulse in a circuit connected to the at least one battery cell,
determining an impedance of the at least one battery cell on the basis of the alternating current pulse, and
determining the state of charge by comparing the impedance to predefined map data, wherein a relationship between the impedance and the state of charge of the at least one battery cell is determined from the predefined map data;
wherein the predetermined map data define at least one calibration point within a curve of an imaginary part of the impedance, wherein an additional detection of the state of charge by current integration is calibrated when the calibration point is exceeded.

2. The method as claimed in claim 1 , wherein a real part of the impedance is compared to real part data, wherein the real part data are part of the map data and wherein a respective value for the state of charge of the at least one battery cell is assigned to multiple values for the real part of the impedance by the real part data.

3. The method as claimed in claim 2 , wherein an imaginary part of the impedance is compared to imaginary part data, wherein the imaginary part data are part of the map data and wherein a respective value for the state of charge of the at least one battery cell is assigned to multiple values for the imaginary part of the impedance by the imaginary part data.

4. The method as claimed in claim 2 , wherein an equivalent circuit diagram of the at least one battery cell is used to determine the impedance, which comprises a parallel connection of a capacitor (C1) and a first resistor (R1) and a second resistor (Ri) in series with said parallel connection.

5. The method as claimed in claim 2 , wherein the impedance is compared to aging map data in addition to the map data, wherein the aging map data indicate a change in the relationship between the impedance and the state of charge due to aging and/or the number of cycles of the at least one battery cell.

6. The method as claimed in claim 1 , wherein an imaginary part of the impedance is compared to imaginary part data, wherein the imaginary part data are part of the map data and wherein a respective value for the state of charge of the at least one battery cell is assigned to multiple values for the imaginary part of the impedance by the imaginary part data.

7. The method as claimed in claim 6 , wherein an equivalent circuit diagram of the at least one battery cell is used to determine the impedance, which comprises a parallel connection of a capacitor (C1) and a first resistor (R1) and a second resistor (Ri) in series with said parallel connection.

8. The method as claimed in claim 6 , wherein the impedance is compared to aging map data in addition to the map data, wherein the aging map data indicate a change in the relationship between the impedance and the state of charge due to aging and/or the number of cycles of the at least one battery cell.

9. The method as claimed in claim 1 , wherein an equivalent circuit diagram of the at least one battery cell is used to determine the impedance, which comprises a parallel connection of a capacitor (C1) and a first resistor (R1) and a second resistor (Ri) in series with said parallel connection.

10. The method as claimed in claim 9 , wherein a local or absolute maximum of an electrical capacitance C of the capacitor (C1) in the equivalent circuit diagram, is used as the at least one calibration point, wherein the local or absolute maximum of the capacitance (C1) is at between 70% and 90% state of charge of the at least one battery cell.

11. The method as claimed in claim 1 , wherein the impedance is compared to aging map data in addition to the map data, wherein the aging map data indicate a change in the relationship between the impedance and the state of charge due to aging and/or the number of cycles of the at least one battery cell.

12. The method as claimed in claim 11 , wherein the aging map data are derived from a direct current resistance of the at least one battery cell.

13. The method as claimed in claim 12 , wherein based on the direct current resistance, a temperature-dependent and/or state-of-charge-dependent characteristic map can be determined which, as part of the aging map data, indicates the change in the relationship between the impedance and the state of charge.

14. A control device for determining a state of charge of at least one battery cell, comprising:
an output unit for outputting a command signal for generating an alternating current pulse in a circuit connected to the at least one battery cell and/or a detection unit for detecting the alternating current pulse in the circuit, and
a determination unit for determining an impedance of the at least one battery cell on the basis of the alternating current pulse,
wherein
the control device is designed to determine the state of charge by comparing the impedance to predefined map data, wherein a relationship between the impedance and the state of charge of the at least one battery cell is determined from the predefined map data, wherein the predetermined map data define at least one calibration point within a curve of an imaginary part of the impedance,
wherein an additional detection of the state of charge by current integration is calibrated when the calibration point is exceeded.

15. A motor vehicle, comprising:
a control device as claimed in claim 14 ,
the at least one battery cell,
the circuit connected to the at least one battery cell, and
an electrical load which is designed to generate the alternating current pulse in the circuit connected to the at least one battery cell in response to the command signal.

16. The motor vehicle as claimed in claim 15 , wherein the at least one battery cell is configured as a lithium iron phosphate cell.

Assignees

• Audi Ag

Inventors

• Kalin Dorothea
• Naumann Rolf
• Roettinger Christian

Classifications

• B60L58/12

  responding to state of charge [SoC] · CPC title

• G01R31/367

  Software therefor, e.g. for battery testing using modelling or look-up tables · CPC title

• H01M10/4257

  Smart batteries, e.g. electronic circuits inside the housing of the cells or batteries · CPC title

• H01M10/4207 Primary

  for several batteries or cells simultaneously or sequentially · CPC title

• G01R31/374

  with means for correcting the measurement for temperature or ageing · CPC title