Protective circuit for a rechargeable battery pack

• US 9,054,533 B2
• Filed: 12/24/2012
• Issued: 06/09/2015
• Est. Priority Date: 12/22/2011
• Status: Active Grant

• Current Assignee: Andreas STIHL AG & Company KG (Stihl Holding AG & Company KG)
• Original Assignee: Andreas STIHL AG & Company KG (Stihl Holding AG & Company KG)
• Inventors: Gaul, Henrik, Liebhard, Gernot
• Primary Examiner(s): Ngo, Brian
• Application Number:
  US13/726,369
• Publication Number:
  US 20130162217A1
• Time in Patent Office: 897 Days
• Field of Search: 320/116, 320/117, 320/118, 320/119, 320/145, 320/162, 320/132, 320/134, 320/125, 320/160
• US Class Current: 1/1
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/486 for measuring temperature
• CPC Class Codes: H02H 7/18 for batteries; for accumulators
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0019 using switched or multiplexed charge circuits
• CPC Class Codes: H02J 7/0029 with safety or protection devices or circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

The invention is directed to a protective circuit for a multiplicity of individual cells arranged in a rechargeable battery pack, wherein a predefined number of individual cells forms a cell network. A monitoring circuit for the state of charge of the individual cells in the cell network is provided wherein the voltage at an individual cell is detected and the detected voltages of a plurality of individual cells are compared among one another to output a signal when an unbalancing limit is exceeded unbalancing limit indicates a permissible voltage difference between two selected individual cells of the cell network. The unbalancing limit of the cell network is provided as a characteristic curve variable over its state of charge. To alter the unbalancing limit, the characteristic curve is altered in dependence on a correction value.

Claims

1. A protective circuit for a multiplicity of individual cells mounted in a rechargeable battery pack wherein a pregiven number of the individual cells form a cell network having at least one operating variable, the protective circuit comprising:

a monitoring circuit for monitoring the charge state of the individual cells of said cell network;

said monitoring circuit, being operatively connected to said individual cells of said cell network for detecting respective voltages (U_na, U_nb, U_nc) applied across corresponding ones of said individual cells;

said monitoring circuit being configured to compare the detected voltage (U_na, U_nb, U_nc) of several of said individual cells of said cell network to each other and output a signal when the comparison exceeds a debalancing limit (U_Dn) assigned to said cell network;

said debalancing limit (U_Dn) specifying a permissible voltage difference (Δ

U_z) between two selected ones of said individual cells of said cell network;

said debalancing limit (U_Dn) being defined as a characteristic line (D) as a function of the charge state (SOC) of said cell network;

a circuit device configured for forming a corrective value in dependence upon said operating variable of said cell network; and

,

said circuit device being further configured for changing said characteristic line (D) in dependence upon said corrective value to change said debalancing limit (U_Dn).

2. The protective circuit of claim 1, wherein said debalancing limit (U_Dn) is formed by the permissible difference voltage (Δ

U_Z) between the voltage (U_na, U_nb, U_nc) of the fullest one of said individual cells of said cell network and the voltage (U_na, U_nb, U_nc) of the emptiest one of said individual cells of said cell network.

3. The protective circuit of claim 2, wherein said cell network has a plurality of said operating variables;

and, said corrective value is formed in dependence upon several ones of said operating variables.

4. The protective circuit of claim 1, wherein said operating variable is a historical operating variable formed from historic values collected in the past during operation of said cell network.

5. The protective circuit of claim 4, wherein said historic operating variable, is a load collective formed over the operating time of said cell network.

6. The protective circuit of claim 5, wherein said historic operating variable is a temperature collective formed over the operating time of said cell network.

7. The protective circuit of claim 6, wherein said cell network is charged up with a charge current (I_L) and said historic operating variable is formed from past charged times having different charge currents (I_L).

8. The protective circuit of claim 7, wherein the detected charge current (I_L) is normalized with reference to the capacity of the charged cell network.

9. The protective circuit of claim 8, wherein said cell network is charged with different charge methods and said historic operating variable is formed from the frequency of occurrence of a first charging method in comparison to another charging method.

10. The protective circuit of claim 4, wherein said historic operating variable is derived from the operation of the rechargeable battery pack with different work apparatus.

11. The protective circuit of claim 4, wherein said historic operating variable has a cyclical ratio of full charges to part charges.

12. The protective circuit of claim 11, wherein the part charge of a cell network corresponds to approximately 70% to 90% of the full charge.

13. The protective circuit of claim 12, wherein the part charge of a cell network corresponds to approximately 80% of the full charge.

14. The protective circuit of claim 1, wherein said operating variable is an instantaneous operating variable detected in a current operation of the rechargeable battery pack.

15. The protective circuit of claim 14, wherein said instantaneous operating variable is the current or present current (I_L) of said cell network.

16. The protective circuit of claim 14, wherein said instantaneous operating variable is the current or present temperature of said cell network.

17. The protective circuit of claim 1, wherein said operating variable is the charge (SOC;

SOCC) stored in a cell network or in one of said individual cells.

18. The protective circuit of claim 17, wherein the charge states of said cell network and/or said one individual cell are evaluated;

and, said charge states are determined over an operating duration of said rechargeable battery pack.

19. The protective circuit of claim 1, wherein said cell network includes a switch;

and, said signal is applied as a control signal for switching off the entire rechargeable battery pack via said switch.

20. The protective circuit of claim 1, wherein the individual cells of said cell network are arranged in several cell rows;

and, said protective circuit further comprises a switch in each of said rows; and

, said circuit device is further configured to drive the switches in corresponding ones of said cell rows.

21. The protective circuit of claim 20, wherein each of said switches is a MOSFET.

22. The protective circuit of claim 1, wherein said cell network connected to an electric work apparatus including an electric motor and a control unit for said electric motor;

and, said control unit is configured to drive said electric motor in dependence upon said signal.

23. The protective circuit of claim 22, wherein said circuit device includes an evaluation unit operatively connected to said monitoring unit and said evaluation unit and said monitoring unit are mounted in said work apparatus.

24. The protective circuit of claim 1, wherein each of said individual cells is based chemically on lithium.

25. The protective circuit of claim 1, wherein each of said individual cells are lithium-ion cells.