Process for determining the state of a battery

• US 5,187,424 A
• Filed: 12/04/1991
• Issued: 02/16/1993
• Est. Priority Date: 10/14/1989
• Status: Expired due to Fees

• Current Assignee: Daimler Chrysler Company LLC (Stellantis NV)
• Original Assignee: Mercedes-Benz AG (Mercedes-Benz Group AG)
• Inventors: Kubler, Rainer, Benz, Klemens
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Dougherty, Thomas M.
• Application Number:
  US07/801,623
• Time in Patent Office: 440 Days
• Field of Search: 320/14, 320/44, 320/48
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3828 using current integration

Abstract

A process for determining the state of a battery by carrying out in a cycle, starting from a specific charging state of the battery, a charging operation and a discharging operation, each with a specific current, the cycle being terminated when the specific charging state is reached again, and the state of the battery being deduced from the difference between the time periods required for the charging operation and the discharging operation. Alternatively, from a specific charging state of the battery a discharge can be carried out, in order to determine the available capacity from the extracted charge.

Claims

1. A process for determining the state of a battery comprising:

controlling a charging/discharging device to place the battery in a specific charging state in which an instantaneous terminal voltage U_act is equal to a predeterminable reference value U_ref2 ;

generating a first signal when the battery has reached the specific charging state;

controlling the charging/discharging device as a function of the first signal such that, during a specific time period t₁, a specific current I₁ flows, the direction of the specific current I₁ corresponding to a discharging operation;

generating a second signal which controls the charging/discharging device such that a specific current I₂, the direction of the specific current I₂ corresponding to a charging operation, flows for a time period t₂ until the battery is again in the specific charging state;

measuring the time period t₂, during which the specific current I₂ flows; and

providing measured data fed to an evaluation unit in which an order of magnitude of the conversion of electrical energy into heat energy is deduced from a deviation of the time t₂ from the time t₁.

2. The process according to claim 1, wherein the currents I₁ and I₂ are equal.

3. The process according to claim 2, wherein the currents I₁ and I₂ are of an order of magnitude which corresponds to maximum currents occurring relatively frequently under customary operating conditions of the battery.

4. The process according to claim 3, wherein the time period t₁ is of the order of magnitude of 15 min.

5. The process according to claim 4, wherein the specific charging state of the battery is approached, at the start of a cycle, by a current having a direction that is identical to the direction of the current I₂.

6. The process according to claim 5, further comprising initially charging or discharging the battery to a charging state in which an instantaneous terminal voltage U_act has such a value that, starting from this charging state, a present terminal voltage U_act of the battery is brought by a current I_V1 to a value which is equal to a reference voltage U_ref1, and in that, starting from this charging state, the present terminal voltage U_act of the battery is brought by a current I_V2, at the start of the cycle, to a value which is equal to the reference voltage U_ref2, the currents I_V1 and I_V2 each having the same direction as the current I₂, the reference voltage U_ref1 being different from the reference voltage U_ref2.

7. The process according to claim 6, wherein the currents I_V1 and I_V2 are of the order of magnitude of the rated current of the battery.

8. The process according to claim 7, further comprising determining a relative capacity Q_rel that represents the state of the battery by multiplying the current I₁ flowing during the discharging operation by the associated time t₁, and by dividing a resulting charge Q_-, extracted from the battery, by the charge Q₊ fed to the battery and obtained by multiplying the current I₂ flowing during the charging operation by the associated time t₂, and in that a low relative capacity Q_rel corresponds to a poor state of the battery.

9. The process according to claim 8, wherein a threshold value Q_relSW is defined for the relative capacity Q_rel, the battery being detected as no longer operative when its relative capacity Q_rel falls below the threshold value Q_relSW.

10. A process for determining the state of a battery comprising:

controlling a charging/discharging device to place the battery in a specific charging state in which an instantaneous terminal voltage U_act is equal to a predeterminable reference value U_ref2 ;

generating a first signal when the battery has reached the specific charging state;

controlling the charging/discharging device as a function of the first signal such that, during a specific time period t₁, a specific current I₁ flows, the direction of the specific current I₁ corresponding to a charging operation;

generating a second signal which controls the charging/discharging device such that a specific current I₂, the direction of the specific current I₂ corresponding to a discharging operation, flows for a time period t₂ until the battery is again in the specific charging state such that the instantaneous terminal voltage U_act is equal to the predeterminable reference value U_ref2 ;

measuring the time period t₂, during which the specific current I₂ flows; and

providing measured data fed to an evaluation unit in which an order of magnitude of the conversion of electrical energy into heat energy is deduced from a deviation of the time t₂ from the time t₁.

11. The process according to claim 10, wherein the currents I₁ and I₂ are equal.

12. The process according to claim 11, wherein the currents I₁ and I₂ are of an order of magnitude which corresponds to maximum currents occurring relatively frequently under customary operating conditions of the battery.

13. The process according to claim 12, wherein the time period t₂ is of the order of magnitude of 15 min.

14. The process according to claim 13, wherein the specific charging state of the battery is approached, at the start of a cycle, by a current having a direction that is identical to the direction of the current I₂.

15. The process according to claim 14, further comprising initially charging or discharging the battery to a charging state in which an instantaneous terminal voltage U_act has such a value that, starting from this charging state, a present terminal voltage U_act of the battery is brought by a current I_V1 to a value which is equal to a reference voltage U_ref1, and in that, starting from this charging state, the present terminal voltage U_act of the battery is brought by a current I_V2, at the start of the cycle, to a value which is equal to the reference voltage U_ref2, the currents I_V1 and I_V2 each having the same direction as the current I₂, the reference voltage U_ref1 being different from the reference voltage U_ref2.

16. The process according to claim 15, wherein the currents I_V1 and I_V2 are of the order of magnitude of the rated current of the battery.

17. The process according to claim 16, further comprising determining a relative capacity Q_rel that represents the state of the battery by multiplying the current I₂ flowing during the discharging operation by the associated time t₂, and by dividing a resulting charge Q_-, extracted from the battery, by the charge Q₊ fed to the battery and obtained by multiplying the current I₁ flowing during the charging operation by the associated time t₁, and in that a low relative capacity Q_rel corresponds to a poor state of the battery.

18. The process according to claim 17, wherein a threshold value Q_relSW is defined for the relative capacity Q_rel, the battery being detected as no longer operative when its relative capacity Q_rel falls below the threshold value Q_relSW.

19. A process for determining the state of a battery, the battery being initially in a state I in which the battery has a final charging voltage at its terminals, comprising:

generating a signal that controls a charging/discharging device to change the battery from state I to a state II by a first discharge current I_SE for a time period t_SE, the battery in state II having a final discharge voltage U_ES at its terminals, and the first discharge current I_SE being clearly above a rated current I_rat of the battery;

measuring the time period t_SE during which the discharge current I_SE flows;

feeding measured data to an evaluation unit;

determining in the evaluation unit a capacity Q_real of the battery by multiplying the first discharge current I_SE by the time period t_SE, and deducing a state of the battery from a deviation of the specific capacity Q_real from a rated capacity Q_rat ;

controlling the charging/discharging device, after the changeover of the battery to the state II by the first discharge current I_SE flowing during the time period t_SE, for a time period delay t_delay, such that neither a charging or a discharging current flows;

controlling the charging/discharging device, after the time period t_delay, such that a second discharge current I_NE flows for a time period t_NE until the battery returns to the state II;

measuring the time period t_NE during which the current I_NE flows;

feeding the measured data to the evaluation unit and calculating the specific capacity Q_real by adding the product I_NE *t_NE to the product I_SE *t_SE.

20. The process according to claim 19, wherein the discharge current I_SE is of an order of magnitude which corresponds to maximum currents occurring relatively frequently under customary operating conditions of the battery.

21. The process according to claim 20, further comprising comparing the calculated capacity Q_rel with the rated capacity Q_rat, and in the event of a deviation of the capacity Q_rel from the rated capacity Q_rat above a threshold value, the battery is detected as no longer operative.

22. The process according to claim 21, further comprising:

when the battery has an instantaneous terminal voltage U_act below the final charging voltage, at the start of process cycle II, charging the battery with a current I_L until the instantaneous terminal voltage U_act is equal to the final charging voltage, and cutting off the process cycle II when the current I_L flows for longer than a predetermined time t_L.

23. The process according to claim 22, wherein the current I_L is clearly above the rated current of the battery.

24. The process according to claim 23, wherein the time t_L is of the order of magnitude of one minute.