Method and apparatus for automatic equalization of series-connected batteries

• US 5,504,415 A
• Filed: 12/03/1993
• Issued: 04/02/1996
• Est. Priority Date: 12/03/1993
• Status: Expired due to Fees

• Current Assignee: Advanced Charger Technology, Inc.
• Original Assignee: Electronic Power Technology Incorporated
• Inventors: Golod, Mikhail B., Podrazhansky, Yury M., Podrazhansky, Mikhail Y.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/162,581
• Time in Patent Office: 851 Days
• Field of Search: 320/17, 320/18
• US Class Current: 320/118
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A method and an apparatus (10) for equalizing the state of charge among a plurality of series-connected batteries (B1-BN). A module (12A-12N) is connected in parallel with each of the batteries (B1-BN), respectively. Each module (12A-12N) contains a voltage divider circuit (40) so that the voltage across a battery may be measured to determine the state of charge, and a circuit (43) which selectively shunts charging current around a battery or applies a discharging current to a battery. A charging transistor (30) applies a charging current to the series of batteries (B1-BN) and, depending upon the state of charge of each battery, a portion of the charging current may be shunted around the battery by its associated module (12) so as to prevent overcharging of the battery. A controller (14) monitors the state of charge of each of the batteries and the temperature of each of the batteries and adjusts the portion of the charging shunted around an individual battery so as to rapidly equalize the state of charge among the different batteries (B1-BN). This process is automatically conducted whenever a charging current is applied to the batteries so that the batteries are maintained in an equalized condition.

Claims

1. A method for equalizing a state of charge among a series-connected first cell and second cell during a charge process wherein a charging current is applied to said series-connected first cell and secured cell, comprising the steps of:

measuring the temperature of said first cell and the temperature of said second cell;

calculating a portion of said charging current to be shunted around said first cell based upon said temperature of said first cell, and a portion of said charging current to be shunted around said second cell based upon said temperature of said second cell; and

shunting around said first cell said portion of said charging current calculated for said first cell, and shunting around said second cell said portion of said charging current calculated for said second cell.

2. The method of claim 1 wherein said charging current is applied for a charging pulse period and said step of calculating is performed before said charging pulse period.

3. A method for equalizing a state of charge for each cell in a plurality of series-connected cells during a charging process wherein a charging current is applied to said plurality of series-connected cells, comprising the steps of:

measuring the temperature of each said cell;

calculating a portion of a charging current to be shunted around each said cell based upon said temperature of that said cell; and

shunting around each said cell said portion of said charging current calculated for that said cell.

4. The method of claim 3 wherein said charging current is applied for a charging pulse period and said step of calculating is performed before said charging pulse period.

5. An apparatus for equalizing a state of charge among a series-connected first cell and second cell during a charging process wherein a charging current is applied to said series-connected first cell and second cell, comprising in combination:

first means for measuring the temperature of said first cell;

second means for measuring the temperature of said second cell;

first means for shunting around said first cell a portion of said charging current;

second means for shunting around said second cell a portion of said charging current; and

controller means responsive to said temperature of said first cell for calculating said portion of said charging current to be shunted around said first cell, and responsive to said temperature of said second cell for calculating said portion of said charging current to be shunted around said second cell, and for controlling said means for shunting around said first cell, and said means for shunting around said second cell.

6. The apparatus of claim 5 wherein said controller causes said first means for measuring and said second means for measuring to measure said temperature when said charging current is not being applied to said series-connected first cell and second cell.