Cell balancing apparatus and method using a voltage variation pattern of each cell to estimate an open circuit voltage value for each cell

• US 9,287,723 B2
• Filed: 12/09/2009
• Issued: 03/15/2016
• 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: Kang, Jung-Soo, Kim, Do-Youn
• Primary Examiner(s): Fantu, Yalkew
• Assistant Examiner(s): HERNANDEZ, MANUEL J
• Application Number:
  US12/634,310
• Publication Number:
  US 20100085009A1
• Time in Patent Office: 2,288 Days
• Field of Search: 320/118
• US Class Current: 1/1
• 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 using a voltage variation pattern of a battery cell, which balances a state of charge (SOC) of a plurality of cells in a battery, the cell balancing apparatus comprising:

an open circuit voltage (OCV) estimating means for measuring a voltage of each cell in the battery and estimating an OCV of each cell using a voltage variation pattern of each cell defined by three output voltages V_n, V_n-1 and V_n-2; and

a cell balancing means for balancing an SOC of each cell by selecting a target cell for balancing through a comparison of the estimated OCV of each cell and controlling a balancing circuit corresponding to the selected cell,

the OCV estimating means comprising;

a voltage measuring unit for measuring the voltage of each cell;

a temperature measuring unit for measuring a 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 Δ

OCV_n(k) 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 F(T) 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,

wherein

Δ

OCV_n(k)=OCV_n(k)−

OCV_n-1(k)=G(V)×

F(T)=[V_n−

V_n-1]×

g(V_n,V_n-1,V_n-2)×

F(T),

wherein g(V_n, V_n−

1, V_n−

2) is a relative ratio of a previous output voltage variation to a present output voltage variation, and

wherein “

n”

is an order index of estimating an OCV variation, and “

k”

is an order index of a cell.

2. The cell balancing apparatus according to claim 1, wherein the OCV estimating unit is configured to correct the estimated OCV by adding a difference between a weighted mean of a plurality of the measured voltages and the previously estimated OCV to the estimated OCV, wherein a higher weighted value is assigned to an earlier measured voltage.

3. The cell balancing apparatus according to claim 1, wherein the cell balancing unit is configured to select, as the target cell for balancing, a cell having the estimated OCV higher than a reference level and operate the balancing circuit corresponding to the selected target cell to discharge the selected target cell.

4. The cell balancing apparatus according to claim 1, wherein the cell balancing unit is configured to select, as the target cell for balancing, a cell having the estimated OCV lower than a reference level and operate the balancing circuit corresponding to the selected target cell to charge the selected target cell.

5. The cell balancing apparatus according to claim 1, wherein the balancing circuit comprises a charge circuit and a discharge circuit, and

wherein the cell balancing unit is configured to select, as the target cell for balancing, a cell having the estimated OCV out of a reference range, operate the balancing circuit corresponding to the selected target cell having the estimated OCV higher than a maximum limit of the reference range to discharge the selected target cell and operate the balancing circuit corresponding to the selected target cell having the estimated OCV lower than a minimum limit of the reference range to charge the selected target cell.

6. A cell balancing apparatus using a voltage variation pattern of a battery cell, which balances a state of charge (SOC) of a plurality of cells in a battery, the cell balancing apparatus comprising:

an OCV estimating means for measuring a voltage of each cell in the battery and estimating an OCV of each cell using a voltage variation pattern of each cell defined by three output voltages V_n, V_n-1 and V_n-2;

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

a cell balancing means for balancing the SOC of each cell by selecting a target cell for balancing through a comparison of the estimated SOC of each cell and controlling a balancing circuit corresponding to the selected cell,

the OCV estimating means comprising;

a voltage measuring unit for measuring the voltage of each cell;

a temperature measuring unit for measuring a 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 Δ

OCV_n(k) 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 F(T) 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,

wherein

Δ

OCV_n(k)=OCV_n(k)−

OCV_n-1(k)=G(V)×

F(T)=[V_n−

V_n-1]×

g(V_n,V_n-1,V_n-2)×

F(T),

wherein g(V_n, V_n-1, V_n-2) is a relative ratio of a previous output voltage variation to a present output voltage variation, and

wherein “

n”

is an order index of estimating an OCV variation, and “

k”

is an order index of a cell.

7. The cell balancing apparatus according to claim 6, wherein the SOC estimating unit is configured to estimate the SOC of each cell by mapping the estimated OCV and the temperature of each cell to a corresponding SOC of each cell using a lookup table including SOC data for each OCV and each temperature.

8. The cell balancing apparatus according to claim 6, wherein the OCV estimating unit is configured to correct the estimated OCV by adding a difference between a weighted mean of a plurality of the measured voltages and the previously estimated OCV to the estimated OCV, wherein a higher weighted value is assigned to an earlier measured voltage.

9. The cell balancing apparatus according to claim 6, wherein the cell balancing unit is configured to select, as the target cell for balancing, a cell having the estimated SOC higher than a reference level and operate the balancing circuit corresponding to the selected target cell to discharge the selected target cell.

10. The cell balancing apparatus according to claim 6, wherein the cell balancing unit is configured to select, as the target cell for balancing, a cell having the estimated SOC lower than a reference level and operate the balancing circuit corresponding to the selected target cell to charge the selected target cell.

11. The cell balancing apparatus according to claim 6, wherein the balancing circuit comprises a charge circuit and a discharge circuit, and

wherein the cell balancing unit is configured to select, as the target cell for balancing, a cell having the estimated SOC out of a reference range, operate the balancing circuit corresponding to the selected target cell having the estimated SOC higher than a maximum limit of the reference range to discharge the selected target cell and operate the balancing circuit corresponding to the selected target cell having the estimated SOC lower than a minimum limit of the reference range to charge the selected target cell.

12. A cell balancing method using a voltage variation pattern of a battery cell, which balances a state of charge (SOC) of a plurality of cells in a battery, the cell balancing method comprising:

measuring a voltage of each cell in the battery and estimating an open circuit voltage (OCV) of each cell using a voltage variation pattern of each cell defined by three output voltages V_n, V_n-1 and V_n-2; and

balancing the SOC of the plurality of cells through a comparison of the estimated OCV of each cell,

the estimating the OCV comprising;

measuring the voltage and a temperature of each cell;

calculating an OCV variation Δ

OCV_n(k) 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 F(T) 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,

wherein

Δ

OCV_n(k)=OCV_n(k)−

OCV_n-1(k)=G(V)×

F(T)=[V_n−

V_n-1]×

g(V_n,V_n-1,V_n-2)×

F(T),

wherein g(V_n, V_n-1, V_n-2) is a relative ratio of a previous output voltage variation to a present output voltage variation, and

wherein “

n”

is an order index of estimating an OCV variation, and “

k”

is an order index of a cell.

13. The cell balancing method according to claim 12, wherein the estimating of the OCV further comprises correcting the estimated OCV by adding a difference between a weighted mean of a plurality of the measured voltages and the previously estimated OCV to the estimated OCV, wherein a higher weighted value is assigned to an earlier measured voltage.

14. The cell balancing method according to claim 12, wherein the operating of the balancing circuit comprises operating the balancing circuit to discharge a cell having the estimated OCV higher than a reference level, to charge a cell having the estimated OCV lower than a reference level, to discharge a cell having the estimated OCV higher than a maximum limit of a reference range or to charge a cell having the estimated OCV lower than a minimum limit of the reference range.

15. A cell balancing method using a voltage variation pattern of a battery cell, which balances a state of charge (SOC) of a plurality of cells in a battery, the cell balancing method comprising:

measuring a voltage of each cell in the battery and estimating an open circuit voltage (OCV) of each cell using a voltage variation pattern defined by three output voltages V_n, V_n-1 and V_n-2;

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

balancing the SOC of the plurality of cells through a comparison of the estimated SOC of each cell,

the estimating the OCV comprising;

measuring the voltage and a temperature of each cell;

calculating an OCV variation Δ

OCV_n(k) 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 F(T) 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,

wherein

Δ

OCV_n(k)=OCV_n(k)−

OCV_n-1(k)=G(V)×

F(T)=[V_n−

V_n-1]×

g(V_n,V_n-1,V_n-2)×

F(T),

wherein g(V_n, V_n-1, V_n-2) is a relative ratio of a previous output voltage variation to a present output voltage variation, and

wherein “

n”

is an order index of estimating an OCV variation, and “

k”

is an order index of a cell.

16. The cell balancing method according to claim 15, wherein the estimating of the SOC estimates the SOC of each cell by mapping the estimated OCV and the temperature of each cell to a corresponding SOC of each cell using a lookup table including SOC data for each OCV and each temperature.

17. The cell balancing method according to claim 15, wherein the operating of the balancing circuit comprises operating the balancing circuit to discharge a cell having the estimated SOC higher than a reference level, to charge a cell having the estimated SOC lower than a reference level, to discharge a cell having the estimated SOC higher than a maximum limit of a reference range or to charge a cell having the estimated SOC lower than a minimum limit of the reference range.

18. A hardware module comprising:

a processor for executing processes of;

measuring a voltage of each cell in a battery and estimating an open circuit voltage (OCV) of each cell using a voltage variation pattern of each cell defined by three output voltages V_n, V_n-1 and V_n-2; and

balancing a state of charge (SOC) of a plurality of cells through a comparison of the estimated OCV of each cell,

the estimating the OCV comprising;

measuring the voltage and a temperature of each cell;

calculating an OCV variation Δ

OCV_n(k) 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 F(T) 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,

wherein

Δ

OCV_n(k)=OCV_n(k)−

OCV_n-1(k)=G(V)×

F(T)=[V_n−

V_n-1]×

g(V_n,V_n-1,V_n-2)×

F(T),

wherein g(Vn, Vn−

1, Vn−

2) is a relative ratio of a previous output voltage variation to a present output voltage variation, and

wherein “

n”

is an order index of estimating an OCV variation, and “

k”

is an order index of a cell.

19. A hardware module comprising:

a processor for executing processes of;

measuring a voltage of each cell in a battery and estimating an open circuit voltage (OCV) of each cell using a voltage variation pattern defined by three output voltages V_n, V_n-1 and V_n-2;

estimating a state of charge (SOC) of each cell from the OCV of each cell; and

balancing an SOC of a plurality of cells through a comparison of the estimated SOC of each cell,

the estimating the OCV comprising;

measuring the voltage and a temperature of each cell;

calculating an OCV variation Δ

OCV_n(k) 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 F(T) 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,

wherein

Δ

OCV_n(k)=OCV_n(k)−

OCV_n-1(k)=G(V)×

F(T)=[V_n−

V_n-1]×

g(V_n,V_n-1,V_n-2)×

F(T),

wherein g(V_n, V_n-1, V_n-2) is a relative ratio of a previous output voltage variation to a present output voltage variation, and

wherein “

n”

is an order index of estimating an OCV variation, and “

k”

is an order index of a cell.