Method and device for balancing charges of a plurality of series-connected battery cells

• US 6,437,539 B2
• Filed: 02/27/2001
• Issued: 08/20/2002
• Est. Priority Date: 03/01/2000
• Status: Expired due to Fees

• Current Assignee: Agence Spatiale Europeenne
• Original Assignee: Agence Spatiale Europeenne
• Inventors: Olsson, Dan Hakan Lennart, Dudley, Geoffrey John
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/794,967
• Publication Number:
  US 20010019256A1
• Time in Patent Office: 539 Days
• Field of Search: 320/116, 320/117, 320/118, 320/119, 320/120, 320/122
• US Class Current: 320/118
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits

Abstract

A method and device for balancing the charges of a plurality of series-connected battery cells, the device comprising a current dissipative loop connected across the terminals of each battery cell, the voltage across each battery cell being measured, the average value of the measured voltages being determined, the measured voltage being then compared to the average value, and the measured voltage of each battery cell being adjusted to the average value so as to equalize charges of all battery cells.

Claims

1. A method for balancing the charges of a plurality of series-connected battery cells, comprising the steps of connecting a current dissipative loop across each battery cell, measuring voltage across each battery cell, determining an average voltage value of said measured voltages, comparing each of said measured voltages to said average voltage value, and for each battery cell, adjusting said measured voltage to said average voltage value so as to equalize the changes of all battery cells.

2. The method according to claim 1, further comprising closing the dissipative loop connected to each of said battery cells if the voltage measured across the battery cell is greater than said average voltage value, and opening the dissipative loop if the voltage measured across said battery cell is lower than said average voltage value.

3. A device for balancing the respective charge currents of a plurality of series-connected battery cells, comprising first means for measuring individual voltages of said battery cells, second means for determining an average voltage of all of said series-connected battery cells, and a control unit for triggering an equalization of said measured voltages with said determined average voltage.

4. A device for balancing the respective charge currents of a plurality of series-connected battery cells, comprising first means for measuring individual voltages of said battery cells, second means for determining an average voltage of all of said series-connected battery cells, a control unit for triggering an equalization of said measured voltages with said determined average voltage, each of said battery cells comprising a current dissipative loop connected to said control unit, and said control unit comprising means for opening the dissipative loop associated with a respective battery cell if the individual voltage of the respective battery cell is lower than said average voltage, and for closing the dissipative loop if the individual voltage of the respective battery cell is greater than said average voltage.

10. The device according to claim 4, further comprising for each of said battery cells, at least one Zener diode which is series-connected within said current dissipative loop so as to avoid discharging of each said cell when its voltage decreases below a given threshold.

5. A device for balancing the respective charge currents of a plurality of series-connected battery cells, comprising first means for measuring individual voltages of said battery cells, second means for determining an average voltage of all of said series-connected battery cells, a control unit for triggering an equalization of said measured voltages with said determined average voltage, and for each said battery cell, a comparator, a first resistor having a first terminal at a first voltage connected to a positive terminal of said comparator via a second resistor, and a second terminal at a second voltage connected to a negative terminal of said comparator via a third resistor, each of said positive and negative terminals of said comparator being additionally connected to a negative and a positive terminal of said cell respectively, via a fourth and a fifth resistor, respectively, and an output of said comparator being connected to a dissipation resistor, whereby a difference between said first voltage and said second voltage corresponds to said average voltage value.

6. The device according to claim 5, wherein the current dissipative loop of each said battery cell is controlled to be closed when the following condition is fulfilled:

11. The device according to claim 5, further comprising for each of said battery cells, a transistor having a base terminal connected to the output of the comparator, and an emitter and a collector terminal connected respectively across the terminals of said cell, a dissipating resistor being provided in series within the current dissipative loop comprising a collector-emitter junction of said transistor T.

12. The device according to claim 11, further comprising for each battery cell, at least one Zener diode connected in series between the output of said comparator and the base terminal of said transistor for increasing a threshold voltage at which the collector-emitter junction of transistor is turned on, and therefore, for avoiding discharging of said cell when the voltage across its terminals decreases below a given threshold.

7. A device for balancing the respective charge currents of a plurality of series-connected battery cells, comprising first means for measuring individual voltages of said battery cells, second means for determining an average voltage of all of said series-connected battery cells, a control unit for triggering an equalization of said measured voltages with said determined average voltage, and for each said battery cell a comparator having a positive and a negative input terminal, each of said terminals being connected to a first resistor and a second resistor, the second resistors being connected to battery terminals, respectively, the first resistors being connected respective to a positive and a negative terminal of said battery cell, and an output of said comparator being connected to one of said battery cell terminals via a dissipation resistor.

8. The device according to claim 7, wherein the second resistors have a resistance which equals n times a resistance of said first resistors with n being a number of battery cells connected in series, and said device further comprising a respective third resistor in parallel to each second resistor, said respective third resistor having a resistance n−

1 times the resistance of the first resistor, and switching means for connecting either said second resistors or said third resistors across the battery terminals, respectively, depending on whether all of said battery cells are operating, or whether one of said battery cells is faulty.

9. The device according to claim 7, wherein the second resistors have a resistance equal to n−

1 times the resistance of the first resistors with n being the number of battery cells connected in series and said device further comprising means for generating a voltage equal to (n−

1)/n times the voltage across the battery terminals, and switching means for applying to the second resistors either the voltage across the battery terminals in case of failure of one of said cells in the battery, or the voltage supplied from the voltage generation means.