Method of controlling charge and discharge of a plurality of batteries

• US 6,346,794 B1
• Filed: 06/09/2000
• Issued: 02/12/2002
• Est. Priority Date: 06/08/1999
• Status: Expired due to Term

• Current Assignee: Lenovo PC International Limited (Lenovo Group Ltd.)
• Original Assignee: International Business Machines Corporation
• Inventors: Odaohhara, Shigefumi
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/591,285
• Time in Patent Office: 613 Days
• Field of Search: 370/116, 370/117, 370/128, 307/64, 307/66
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0013 acting upon several batteries simultaneously or sequentially H02J7/1423 takes precedence
• CPC Class Codes: H02J 7/0024 Parallel/serial switching of connection of batteries to charge or load circuit
• CPC Class Codes: H02J 7/0025 Sequential battery discharge in systems with a plurality of batteries
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors

Abstract

Disclosed is a method for controlling efficient charge and discharge of a plurality of batteries. At the beginning of the discharge cycle, parallel discharge of the rechargeable batteries is performed until the batteries discharge to a predetermined percentage of total capacity. Following, serial discharge is performed with the secondary battery being fully discharged before the primary battery is discharged. Thus, the rechargeable batteries respectively are each at least partially discharged at start of charging. When charging commences, the rechargeable batteries are first charged serially until predetermined percentages of capacity are realized. The serial charging is performed with full constant current. Following, the batteries are charged in parallel utilizing a constant voltage whereby the current decreases as the respective capacities approach 100%. As a result, the plurality of batteries are charged more efficiently and in a shorter time than if charge individually or serially.

Claims

1. A method of controlling charge and discharge of two or more rechargeable batteries, said method comprising the steps of:

concurrently discharging a first battery and a second battery to a predetermined percentage of total capacity of each battery;

in response to a charge of said first battery reaching said predetermined percentage of total capacity, stopping a discharging of said first battery, while continuing to discharge said second battery; and

responsive to said second battery being completely discharged, automatically resuming said discharging of said first battery.

2. The method of claim 1, further comprising the steps of:

in response to a detection of a connection to an external power supply, serially charging said first battery and then said second battery to respective predetermined serial charging percentages of total capacity; and

in response to said second battery being charged to its predetermined serial-charging percentage of total capacity, initiating concurrent charging of said first and second battery to a charge value above said predetermined serial charging percentages.

3. The method of claim 2, further comprising calculating said predetermined percentages and said predetermined serial charging percentages based on a charging current equal to half of a nominal capacity of said first and second batteries, respectively.

4. The method of claim 3, wherein:

said serial charging step includes charging each of said first and second batteries at a constant current that is associated with a maximum capacity of respective ones of said first and second batteries; and

said initiating step includes charging said first and second batteries at a constant voltage once said pre-determined serial charging percentages are reached.

5. The method of claim 4, further comprising:

gradually decreasing a charging current over time while said batteries are being charged at said constant voltage; and

switching from a serial charging of said batteries to a parallel charging when a value of said charging current reaches one-half of said constant current value.

6. The method of claim 5, wherein said two or more rechargeable batteries are lithium ion batteries and the value utilized for said constant current is equal to 70% of the maximum constant current possible with said nominal capacity.

7. A system for controlling charge and discharge of two or more rechargeable batteries, comprising:

means for concurrently discharging a first battery and a second battery in parallel to a predetermined percentage of total capacity of each battery;

means, responsive to a charge of said first battery reaching a pre-determined percentage of total capacity, for stopping a discharging of said first battery, while continuing to discharge said second battery; and

means, responsive to said second battery being completely discharged, for automatically resuming said discharging of said first battery.

8. The system of claim 7, further comprising:

means, responsive to a detection of a connection to an external power supply, serially charging said first battery and then said second battery to respective predetermined serial charging percentages of total capacity; and

means, responsive to said second battery being charged to its predetermined serial-charging percentage of total capacity, initiating concurrent charging of said first and second battery to a charge value above said predetermined serial charging percentages.

9. The system of claim 8, further comprising means for calculating said predetermined percentages and said predetermined serial charging percentages based on a charging current equal to half of a nominal capacity of said first and second batteries, respectively.

10. The system of claim 9, wherein:

said serial charging means includes means for charging each of said first and second batteries at a constant current that is associated with a maximum capacity of respective ones of said first and second batteries; and

said initiating means includes means for charging said first and second batteries at a constant voltage once said pre-determined serial charging percentages are reached.

11. The system of claim 10, further comprising:

means for gradually decreasing a charging current over time while said batteries are being charged at said constant voltage; and

means for switching from a serial charging of said batteries to a parallel charging when a value of said charging current reaches one-half of said constant current value.

12. The system of claim 11, wherein said two or more rechargeable batteries are lithium ion batteries and the value utilized for said constant current is equal to 70% of the maximum constant current possible with said nominal capacity.

13. A computer program product for controlling operation of a charge and discharge circuit for two or more rechargeable batteries, said program product comprising:

a computer readable medium;

program instructions provided via said computer readable medium for;

concurrently discharging a first battery and a second battery to a predetermined percentage of total capacity of each battery;

in response to a charge of said first battery reaching said predetermined percentage of total capacity, stopping a discharging of said first battery, while continuing to discharge said second battery; and

responsive to said second battery being completely discharged, automatically resuming said discharging of said first battery.

14. The computer program product of claim 13, further comprising program instructions for:

in response to a detection of a connection to an external power supply, serially charging said first battery and then said second battery to respective predetermined serial charging percentages of total capacity; and

in response to said second battery being charged to its predetermined serial-charging percentage of total capacity, initiating concurrent charging of said first and second battery to a charge a value above said predetermined serial charging percentages.

15. The computer program product of claim 14, further comprising program instructions for calculating said predetermined percentages and said predetermined serial charging percentages based on a charging current equal to half of a nominal capacity of said first and second batteries, respectively.

16. The computer program product of claim 15, wherein:

said serial charging program instructions includes instructions for charging each of said first and second batteries at a constant current that is associated with a maximum capacity of respective ones of said first and second batteries; and

said initiating program instructions includes instructions for charging said first and second batteries at a constant voltage once said pre-determined serial charging percentages are reached.

17. The computer program product of claim 16, further comprising program instructions for:

gradually decreasing a charging current over time while said batteries are being charged at said constant voltage; and

switching from a serial charging of said batteries to a parallel charging when a value of said charging current reaches one-half of said constant current value.

18. An electronic circuit comprising:

a plurality of battery terminal pairs including a pair for a first battery and a pair for a second battery, wherein each battery terminal pair includes a high voltage positive terminal and a negative terminal biased at substantially zero voltage; and

means for controlling a discharge of said first and second batteries, wherein;

p2 said first and second batteries are discharged in parallel when their respective charges are above a predetermined percentage of their associated capacity; and

said second battery is discharged serially before said first battery when a charge of said second battery falls to said predetermined percentage.

19. The electronic circuit of claim 18, wherein said means for controlling includes:

a first pair of transistors coupled in series between a positive terminal of said first battery and a DC/DC converter circuit, wherein said transistors include first internal switching elements;

a first switching element coupled to a first one of said transistors, which is directly coupled to said first battery, wherein said first switching element is coupled in parallel with a corresponding internal switching element of said first one of said transistors and carries a forward voltage, which is smaller than a forward voltage of said corresponding internal switching element;

a second pair of transistors coupled in series between a positive terminal of said second battery and said DC/DC converter circuit, wherein said transistors include second internal switching elements; and

a second switching element coupled to a first one of said second pair of transistors that is directly coupled to said second battery, wherein said first switching element is coupled in parallel with a second corresponding internal switching element of said first one of said second pair of transistors and carries a forward voltage, which is smaller than a forward voltage of said second corresponding internal switching element.

20. The electronic circuit of claim 19 wherein said first switching element and said second switching element are Schottky barrier diodes.

21. The electronic circuit of claim 18, wherein said means for controlling includes a data processing system coupled to said circuit which directs said discharging functions.

22. An electronic circuit, comprising:

a plurality of battery terminal pairs including a pair for a first battery and a pair for a second battery, wherein each battery terminal pair includes a high voltage positive terminal and a negative terminal biased at substantially zero voltage;

an AC adapter biased at one terminal at substantially zero voltage; and

means for efficiently charging said first battery and said second battery using an alternating current source connected to said AC adapter, said means serially charging said first battery followed by said second battery, wherein said first battery and said second battery are charged to respective predetermined serial charging percentages of total capacity and, in response to a charge of said second battery reaching said predetermined serial charging percentage, charging said first and second battery concurrently.

23. The electronic circuit in claim 22 wherein said means for efficiently charging includes:

a charger respectively coupled to said AC adapter and to said positive terminals of said first and said second batteries via connectors, which comprise a switch and a diode;

a first and second pair of series connected resistors with a first end coupled to ground and a second end coupled to said connectors, respectively, between said diode and said positive terminal; and

a voltage feedback control circuit, which is connected between a first and second resistor of both of said first and second pair of series connected resistors, said voltage feedback control circuit being further coupled to said charger and controls the charging of said plurality batteries connected to said plurality of battery terminal pairs by serially charging said first battery then said second battery up to a predetermined capacity, and then parallel-charging both batteries.

24. The electronic circuit of claim 22, further comprising a data processing system coupled to said voltage feedback control circuit by which said charging functions are directed.

25. A method of controlling charge and discharge of a plurality of rechargeable batteries having the same capacity, in which a maximum charging current is equal to xC, where x is a positive real number, said method comprising the steps of:

performing parallel discharge of the plurality of rechargeable batteries and stopping the parallel discharge when a current for charging each rechargeable battery substantially becomes (½

)xC;

responsive to said current becoming substantially (½

)xC, performing serial discharge of the plurality of rechargeable batteries by discharging the plurality of rechargeable batteries one by one until a remaining charge of each rechargeable battery reaches a predetermined value;

responsive to a detection of a power source, serially charging the rechargeable batteries one by one through constant-current charge, wherein said serially charging is performed until a current associated with a charge of each of said plurality of rechargeable battery substantially becomes (½

)xC; and

responsive to said current becoming (½

)xC during charging, performing parallel charging of the rechargeable batteries with constant-voltage.

26. The method of claim 25, wherein said plurality of rechargeable batteries include a main battery and an auxiliary battery, said method further comprising the steps of:

discharging the main battery when a remaining capacity of the auxiliary battery becomes substantially equal to zero;

charging the main battery through constant-current charge and constant-voltage charge, whereon the main battery is charged until a current for charging the main battery substantially becomes (½

)xC;

charging the auxiliary battery through constant-current charge and constant-voltage charge, whereon the auxiliary battery is charged until a value of a current for charging the auxiliary battery substantially becomes (½

)xC; and

responsive to the charging current for both the main battery and auxiliary battery reaching (½

)xC, performing parallel charging of the main battery and the auxiliary battery and continuing said parallel charging until each battery is fully charged.