CELL BALANCING APPARATUS AND METHOD

• US 20100085009A1
• Filed: 12/09/2009
• Published: 04/08/2010
• Est. Priority Date: 08/08/2008
• Status: Active Grant

• Current Assignee: LG Energy Solution Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Kim, Do-Youn, Kang, Jung-Soo
• Granted Patent: US 9,287,723 B2
• Time in Patent Office: Days
• US Class Current: 320/118
• CPC Class Codes: G01R 31/3835 involving only voltage 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: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0019 using switched or multiplexed charge circuits
• 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 is a cell balancing apparatus and method using a voltage variation pattern of a battery cell, which measures voltage of each cell, estimates OCV or SOC of each cell using a voltage variation pattern of each cell including a present voltage and a past voltage, and eliminates a deviation in OCV or SOC between the cells through comparison of the estimated OCV or SOC of each cell. In estimating the OCV of each cell, an output voltage error due to IR drop is corrected. Thus, SOC of each cell may be accurately estimated. And, an accurate estimation of SOC may render substantial elimination for a SOC deviation of each cell. Furthermore, SOC estimating using an output voltage leads to an active cell balancing even during charge and discharge of battery, thereby minimizing an SOC deviation of each cell.

Claims

1. A cell balancing apparatus, comprising:

an open circuit voltage (OCV) estimating means for measuring voltage of each cell in a battery and estimating OCV of each cell using a voltage variation pattern of each cell including a present voltage and a past voltage; and

a cell balancing means for balancing state of charge (SOC) of each cell through comparison of the estimated OCV of each cell.

3. The cell balancing apparatus according to claim 1,

wherein the OCV estimating means comprises:

a voltage measuring unit for measuring voltage of each cell;

a temperature measuring unit for measuring temperature of each cell;

a data storing unit for periodically receiving the voltage and temperature of each cell from the voltage measuring unit and the temperature measuring unit and storing the voltage and temperature in a memory unit;

an OCV variation estimating unit for estimating a present OCV variation of each cell by calculating an OCV variation of each cell from the voltage variation pattern including a present voltage and a past voltage, stored in the memory unit, using a mathematical model that defines a correlation between the output voltage variation pattern and the OCV variation, and reflecting a correction factor corresponding to the temperature of each cell on the calculated OCV variation of each cell; and

an OCV estimating unit for estimating a present OCV of each cell by reflecting the calculated OCV variation of each cell on a previous OCV of each cell.

5. The cell balancing apparatus according to claim 1,

wherein the OCV estimating unit corrects the OCV by adding a difference between a weighted mean (a higher weighted value is assigned to an earlier measured voltage) of a present voltage and a past voltage, and a previously estimated OCV to a presently estimated OCV.

6. The cell balancing apparatus according to claim 5,

wherein the past voltage is a previous voltage.

7. The cell balancing apparatus according to claim 1,

wherein assuming that a present voltage is V_n, an n−

1^th voltage is V_n-1 and an n−

2^th voltage is V_n-2, the present voltage and the past voltage comprise V_n, V_n-1 and V_n-2.

8. The cell balancing apparatus according to claim 1,

wherein the cell balancing means balances SOC of each cell by selecting a target cell for balancing and controlling a balancing circuit corresponding to the selected cell.

9. The cell balancing apparatus according to claim 8,

wherein the balancing circuit is a discharge circuit, and

wherein the cell balancing means selects, as a target cell for balancing, a cell having a higher OCV or SOC than a reference level, and operates a discharge circuit corresponding to the selected cell to decrease SOC of the cell.

10. The cell balancing apparatus according to claim 8,

wherein the balancing circuit is a charge circuit, and

wherein the cell balancing means selects, as a target cell for balancing, a cell having a lower OCV or SOC than a reference level, and operates a charge circuit corresponding to the selected cell to increase SOC of the cell.

11. The cell balancing apparatus according to claim 8,

wherein the balancing circuit comprises a charge circuit and a discharge circuit, and

wherein the cell balancing means selects, as a target cell for balancing, a cell having OCV or SOC out of a reference range, switches a balancing circuit corresponding to a selected cell having a higher OCV or SOC than a maximum limit of the reference range to a discharge circuit to decrease SOC of the cell, and switches a balancing circuit corresponding to a selected cell having a lower OCV or SOC than a minimum limit of the reference range to a charge circuit to increase the SOC of the cell.

12. The cell balancing apparatus according to claim 3,

wherein the estimated OCV variation is calculated by multiplying the calculated OCV variation by the correction factor.

13. The cell balancing apparatus according to claim 3,

wherein the mathematical model is defined by mathematical calculation of a pattern function that is defined by each voltage constituting a voltage variation pattern and a voltage variation between a present voltage and a previous voltage.

14. The cell balancing apparatus according to claim 3,

wherein the correction factor is calculated by substituting temperature of each cell in a mathematical model with a temperature as an input parameter and a correction factor of an OCV variation as an output parameter.

2. A cell balancing apparatus, comprising:

an OCV estimating means for measuring voltage of each cell in a battery and estimating OCV of each cell using a voltage variation pattern of each cell including a present voltage and a past voltage;

a SOC estimating means for estimating SOC of each cell from the OCV of each cell; and

a cell balancing means for balancing SOC of each cell through comparison of the estimated SOC of each cell.

4. The cell balancing apparatus according to claim 2,

wherein the SOC estimating means estimates SOC of each cell by mapping the OCV and temperature of each cell to a corresponding SOC of each cell using a lookup table including SOC data for each OCV and each temperature.

15. A cell balancing method, comprising the steps of:

measuring voltage of each cell in a battery and estimating OCV of each cell using a voltage variation pattern of each cell including a present voltage and a past voltage; and

balancing SOC of the cells through comparison of the estimated OCV of each cell.

17. The cell balancing method according to claim 15,

wherein the OCV estimating step comprises the steps of:

measuring voltage and temperature of each cell;

calculating an OCV variation of each cell from the voltage variation pattern using a mathematical model that defines a correlation between the output voltage variation pattern and the OCV variation;

estimating a present OCV variation of each cell by reflecting a correction factor corresponding to the temperature of each cell on the calculated OCV variation of each cell; and

estimating a present OCV of each cell by reflecting the calculated OCV variation of each cell on a previous OCV of each cell.

19. The cell balancing method according to claim 15,

wherein the OCV estimating step further comprises a step of correcting the OCV by adding a difference between a weighted mean (a higher weighted value is assigned to an earlier measured voltage) of a present voltage and a past voltage, and a previously estimated OCV to a presently estimated OCV.

20. The cell balancing method according to claim 19,

wherein the past voltage is a previous voltage.

21. The cell balancing method according to claim 15,

wherein assuming that a present voltage is V_n, an n−

1^th voltage is V_n-1 and an n−

2^th voltage is V_n-2, the present voltage and the past voltage comprise V_n, V_n-1 and V_n-2.

22. The cell balancing method according to claim 15,

wherein the cell balancing step comprises the steps of:

selecting a target cell for balancing; and

operating a balancing circuit corresponding to the selected cell.

23. The cell balancing method according to claim 15,

wherein the cell balancing step discharges a cell having a higher OCV or SOC than a reference level, charges a cell having a lower OCV or SOC than a reference level, or in the case of a cell having OCV or SOC out of a reference range, discharges a cell having a higher OCV or SOC than a maximum limit of the reference range and charges a cell having a lower OCV or SOC than a minimum limit of the reference range.

24. The cell balancing method according to claim 17,

wherein the estimated OCV variation is calculated by multiplying the calculated OCV variation by the correction factor.

25. The cell balancing method according to claim 17,

wherein the mathematical model is defined by mathematical calculation of a pattern function that is defined by a voltage variation between a present voltage and a previous voltage, and each voltage constituting a voltage variation pattern.

26. The cell balancing apparatus according to claim 17,

wherein the correction factor is calculated by substituting temperature of each cell in a mathematical model with a battery temperature as an input parameter and a correction factor of an OCV variation as an output parameter.

16. A cell balancing method, comprising the steps of:

measuring voltage of each cell in a battery and estimating OCV of each cell using a voltage variation pattern including a present voltage and a past voltage;

estimating SOC of each cell from the OCV of each cell; and

balancing SOC of the cells through comparison of the estimated SOC of each cell.

18. The cell balancing method according to claim 16,

wherein the SOC estimating step estimates SOC of each cell by mapping the OCV and temperature of each cell to a corresponding SOC of each cell using a lookup table including SOC data for each OCV and each temperature.

27. A hardware module for executing the processes of:

measuring voltage of each cell in a battery and estimating OCV of each cell using a voltage variation pattern of each cell including a present voltage and a past voltage; and

balancing SOC of each cell through comparison of the estimated OCV of each cell.

28. A hardware module for executing the processes of:

measuring voltage of each cell in a battery and estimating OCV of each cell using a voltage variation pattern of each cell including a present voltage and a past voltage;

estimating SOC of each cell from the OCV of each cell; and

balancing SOC of each cell through comparison of the estimated SOC of each cell.