BATTERY MANAGEMENT SYSTEM

• US 20080233469A1
• Filed: 02/11/2008
• Published: 09/25/2008
• Est. Priority Date: 02/09/2007
• Status: Abandoned Application

• Current Assignee: Advanced Lithium Power Inc.
• Original Assignee: Advanced Lithium Power Inc.
• Inventors: Drozdz, Piotr, Gettel, Lorne Edward, Simmonds, Stewart Neil
• Application Number:
  US12/029,246
• Publication Number:
  US 20080233469A1
• Time in Patent Office: Days
• US Class Current: 429/61
• CPC Class Codes: B60L 50/64 Constructional details of batteries specially adapted for electric vehicles
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 50/213 adapted for cells having curved cross-section, e.g. round or elliptic H01M50/209, H01M50/216 take precedence
• CPC Class Codes: H01M 50/269 Mechanical means for varying the arrangement of batteries or cells for different uses, e.g. for changing the number of batteries or for switching between series and parallel wiring methods or arrangements for servicing or maintenance H01M6/50, H01M10/42
• CPC Class Codes: H01M 50/569 Constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals battery terminal connectors with integrated measuring arrangements G01R31/364
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/00712 the cycle being controlled or terminated in response to electric parameters
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

Disclosed herein is a battery management system for lithium ion batteries capable of determining a battery pack'"'"'s state of capacity; determining a battery pack'"'"'s state of charge limits; adjusting for voltage drops and power losses over a battery'"'"'s internal and/or connector impedances; adjusting the upper and lower voltage limits of a battery pack; and of actively balancing the cells making up the battery pack. In order to achieve this functionality, the battery pack management system includes an electronic control unit, which unit is coupled to module and cell-level circuitry that is designed to measure operating conditions of the battery such as voltage and current at any given time.

Claims

1. A battery management system for determining a state of capacity of a lithium ion cell comprising:

a) a voltage detector coupled to the cell for obtaining first and second terminal voltage measurements of the cell;

b) a coulomb detector coupled to the cell for counting the number of coulombs discharged from the cell during a controlled discharge of the cell that occurs between the first and second terminal voltage measurements;

c) an electronic control unit coupled to the voltage and coulomb detectors, the electronic control unit calculating the state of capacity of the cell from the number of coulombs discharged from the cell during the controlled discharge and from the first and second terminal voltage measurements of the cell.

2. A battery management system as claimed in claim 1 wherein the terminal voltage measurements are open circuit terminal voltage measurements.

3. A method of determining a state of capacity of a lithium ion cell comprising:

a) determining a first state of charge of the cell;

b) performing a controlled discharge of the cell;

c) counting charge discharged from the cell during the controlled discharge;

d) determining a second state of charge of the cell; and

e) calculating the state of capacity of the cell based on the charge discharged from the cell during the controlled discharge and on the difference between the first state of charge and the second state of charge.

4. A method of determining a state of capacity of a lithium ion cell as claimed in claim 3 wherein the steps of determining the first and second states of charge of the cell are accomplished by reading first and second open circuit voltages of the cell and correlating the first and second open circuit voltages to the first and second states of charge, respectively.

5. A method of determining a state of capacity of a lithium ion cell as claimed in claim 4 wherein the step of calculating the state of capacity of the cell comprises determining the total capacity of the cell using the following equation:

Total Capacity=(Charge Discharged During Controlled Discharge)/[(First State of Charge)−

(Second State of Charge)]

6. A battery management system for balancing the state of charge of cells in series of a battery pack, the system comprising:

a) a voltage detector coupled to the cells for measuring a voltage of each cell of the battery pack;

b) a switch in communication with a selected cell for allowing current to flow from the selected cell of the battery pack;

c) a load resistor in communication with the selected cell for receiving the current flow from the selected cell; and

d) a cell balancing integrated circuit in communication with the voltage detector, the switch and the load resistor, the cell balancing integrated circuit calculating a reference voltage of the cells of the battery pack VREF based on the measured voltage of each cell, determining which cell of the battery pack has a higher voltage than VREF, and discharging the cell with a higher voltage than VREF by closing the switch associated with the cell that has a higher voltage than VREF until the voltage of cell that has a higher voltage than VREF has a voltage substantially equal to VREF.

7. A system as claimed in claim 6 wherein the switch is a transistor.

8. A system as claimed in claims 7 wherein the electronic control unit discharges the cell that has a higher voltage than V_REF when a capacity of the battery pack is between 10% and 90%.

9. A system as claimed in claim 8 wherein V_REF is an average voltage of the cell of the battery pack.

10. A system as claimed in claim 8 wherein V_REF is a lowest voltage of the cells of the battery pack.

11. A method of balancing the state of charge of cells in series of a battery pack comprising the steps of:

a) measuring the voltage of each cell in the battery pack;

b) determining a reference voltage of the cells of the battery pack VREF; and

c) discharging any cell which has a voltage higher than VREF on to a load until the voltage of that cell is substantially equal to VREF.

12. A method as claimed in claim 11 wherein the step of discharging any cell which has a voltage higher than V_REF is performed when the capacity of the battery pack is between 10% and 90%.

13. A system as claimed in claim 12 wherein V_REF is an average voltage of the cell of the battery pack.

14. A system as claimed in claim 12 wherein V_REF is a lowest voltage of the cells of the battery pack.

15. A battery management system for adjusting the state of charge limits on a lithium ion cell comprising

a) a voltage detector coupled to the cell for measuring a terminal voltage of the cell;

and

b) an electronic control unit in communication with the voltage detector, the electronic control unit determining an operating range of the cell and calculating the terminal voltages that correspond to the operating range.

16. A method of adjusting the state of charge limits on a lithium ion cell comprising

a) obtaining an operating range of a lithium ion cell;

and

b) adjusting the terminal voltage of the cell to correspond to the operating range.

17. A battery management system for adjusting an upper voltage limit VUL and a lower voltage limit VLL of a lithium ion cell, the system comprising:

a current detector in communication with the cell for measuring the current flowing through the cell ICELL; and

an electronic control unit in communication with the current detector, the electronic control unit having the internal resistance of the cell Rinternal, VUL and VLL, the electronic control unit calculating a modified upper voltage limit VUL′ and

a modified lower voltage limit VLL′

from VUL, VLL, ICELL, and Rinternal.

18. A battery management system as claimed in claim 17 wherein the cell is being charged and the electronic control unit calculates V_UL′

and V_LL′

using the following equations

VUL′

=VUL+(Rinternal)*ICELL

VLL′

=VLL+(Rinternal)*ICELL

19. A battery management system as claimed in claim 17 wherein the cell is being discharged and the electronic control unit calculates V_UL′

and V_LL′

using the following equations

VUL′

=VUL−

(Rinternal)*ICELL

VLL′

=VLL−

(Rinternal)*ICELL

20. A method of adjusting an upper voltage limit V_UL and a lower voltage limit V_LL of a lithium ion cell comprising the steps of

a) measuring the current flowing through the cell ICELL;

b) calculating a modified upper voltage limit VUL′ and

a modified lower voltage limit VLL′

from VUL, VLL, ICELL, and a known internal resistance of the cell Rinternal.

21. A method as claimed in claim 20 wherein the cell is being charged and the step of calculating a modified upper voltage limit V_UL′

and a modified lower voltage limit V_LL′

utilizes the following equations

VUL′

=VUL+(Rinternal)*ICELL

VLL′

=VLL+(Rinternal)*ICELL

22. A method as claimed in claim 20 wherein the cell is being discharged and the step of calculating a modified upper voltage limit V_UL′

and a modified lower voltage limit V_LL′

utilizes the following equations

VUL′

=VUL−

(Rinternal)*ICELL

VLL′

=VLL−

(Rinternal)*ICELL

23. A battery management system for modifying a capacity of a lithium ion cell based on current flowing through the cell, the battery management system comprising:

a current detector for measuring the current flowing through the battery pack I;

an electronic control unit having the internal impedance of the battery pack Z, the electronic control unit calculating power loss Plo as a result of Z using formula II

I2×

Z=Plo 

 

(II); and

the electronic control unit adapted to decrease the capacity of the cell by an amount proportional to Plo.

24. A method of modifying a capacity of a lithium ion cell based on current flowing through the cell, the method comprising the steps of:

a) measuring the current flowing through the cell I;

b) calculating power loss Plo based on a known internal impedance of the battery pack Z, using formula 11

I2×

Z=Plo 

 

(II); and

c) decreasing the capacity of the cell by an amount proportional to Plo.