Battery equalization circuit with ramp converter and selective outputs

• US 5,982,143 A
• Filed: 05/16/1997
• Issued: 11/09/1999
• Est. Priority Date: 08/27/1996
• Status: Expired due to Fees

• Current Assignee: University of Toledo
• Original Assignee: University of Toledo
• Inventors: Stuart, Thomas A.
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US08/857,410
• Time in Patent Office: 907 Days
• Field of Search: 320/116, 320/117, 320/118, 320/119, 320/121, 320/122, 320/FOR 104, 320/FOR 114, 320/FOR 115, 320/FOR 117, 320/DIG. 29
• US Class Current: 320/119
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/0018 using separate charge circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

An electronic battery equalization circuit that equalizes the voltages of a plurality of series connected batteries in a battery pack. The current waveform is in the shape of a ramp for providing zero current switching. The transformer has a primary winding circuit and at least one secondary winding circuit. In one embodiment, each secondary winding circuit is connected to a different pair of batteries. The equalizing current is provided to the lowest voltage batteries in one half of the battery pack during one half of the charging cycle. The equalizing current is then provided to the lowest voltage batteries in the other half of the battery pack during the other half of the charging cycle. In another embodiment, each secondary winding circuit is connected to a different single battery. The equalizing current is supplied to a lowest voltage battery in the battery pack during each half of the switching cycle. The electronic battery equalization circuit also includes a feedback control circuit coupled to the primary winding circuit for controlling the current from the equalizing current supply source. In another embodiment, optically coupled switches are connected to a battery voltage monitor to provide equalizing current to the lowest voltage even and odd numbered battery in the battery pack.

Claims

1. A battery management system for equalizing voltages a plurality of batteries in a battery pack, comprising:

a battery charger for supplying a charging current to a plurality of batteries in a battery pack during a first half cycle and a second half cycle;

a battery voltage monitor having a microcontroller for monitoring voltages of the plurality of batteries; and

a battery voltage equalizer including an electronic battery equalization circuit for equalizing voltages of the plurality of batteries, said electronic battery equalization circuit further comprising;

a transformer connected to said battery charger;

a primary circuit connected to said transformer; and

at least one secondary circuit connected to said transformer and including at least one optically coupled switch electrically coupled to the microcontroller of said battery voltage monitor,

wherein the microcontroller determines a voltage of the different pair of batteries during the first half cycle and a different pair of batteries during the second half cycle.

2. The battery management system according to claim 1, wherein the microcontroller determines a voltage of the different pair of batteries by comparing the voltage of the different pair of batteries during each half cycle with a reference voltage.

3. The battery management system according to claim 1, wherein the microcontroller supplies charging current to a lowest voltage battery among even-numbered batteries in the battery pack.

4. The battery management system according to claim 1, wherein the microcontroller supplies charging current to a lowest voltage battery among odd-numbered batteries in the battery pack.

5. The battery management system according to claim 1, wherein the charging current is supplied to the plurality of batteries using zero voltage switching.

6. The battery management system according to claim 1, wherein the primary circuit further comprises a negative feedback control circuit coupled to the current transformer.

7. The electronic battery equalization circuit according to claim 6, further comprising a short circuit protection system coupled to said negative feedback control circuit.

8. An electronic battery equalization circuit, comprising:

a current source for supplying a charging current during a first half cycle and a second half cycle;

a transformer connected to said current source;

a primary circuit connected to said transformer, said primary circuit comprising a primary winding, an inductor connected in series to the primary winding, a current transformer connected in series to the inductor and a pair of semiconductor devices; and

at least one secondary circuit connected to said transformer, said secondary circuit comprising a secondary winding being coupled to a different pair of batteries of the plurality of batteries, a pair of diodes connected in series, each diode being connected to a different battery of the plurality of batteries, and at least one optically coupled switch electrically connected to the at least one diode of the pair of diodes,

wherein the charging current is supplied to a lowest voltage odd-numbered battery in the battery pack during the first half cycle, and

wherein the charging current is supplied to a lowest voltage even-numbered battery in the battery pack during the second half cycle.

9. The electronic battery equalization circuit according to claim 8, wherein the charging current is supplied to the plurality of batteries using zero voltage switching.

10. The electronic battery equalization circuit according to claim 8, wherein the primary circuit further comprises a negative feedback control circuit coupled to the current transformer.

11. The electronic battery equalization circuit according to claim 10, wherein said feedback control circuit comprises an error amplifier coupled to the current transformer, a voltage controlled oscillator coupled to the error amplifier and a driver coupled to the voltage controlled oscillator for outputting a drive signal to the pair of semiconductor devices.

12. The electronic battery equalization circuit according to claim 11, wherein the error amplifier compares the charging current to a reference charging current and outputs a signal to the voltage controlled oscillator representing a difference between the charging current and the reference charging current.

13. The electronic battery equalization circuit according to claim 10 further comprising a short circuit protection system coupled to said negative feedback control circuit.

14. The battery equalization circuit according to claim 8, wherein said at least one secondary circuit further comprises a capacitor being connected across the different battery of the plurality of batteries.

15. A method for equalizing voltages of a plurality of batteries in a battery pack using an battery management system comprising a battery charger for supplying a charging current, a battery voltage monitor having a microcontroller and a battery equalization circuit, the battery equalization circuit comprising a transformer connected to the battery charger, a primary circuit connected to the transformer, and at least one secondary circuit connected to the transformer, the secondary circuit comprising a secondary winding being coupled to a different pair of batteries, a diode connected to a different battery, and an optically coupled switch coupled to the battery voltage monitor, the method comprising the steps of:

monitoring a voltage of at least one battery of the plurality of batteries in the battery pack using the microcontroller;

supplying the charging current to a lowest voltage odd-numbered battery in the battery pack during the first half cycle; and

supplying the charging current to a lowest voltage even-numbered battery in the battery pack during the second half cycle.

16. A method for charging a plurality of batteries according to claim 15, further comprising the step of comparing the voltage of the odd-numbered battery with a reference voltage during the first half cycle.

17. A method for charging a plurality of batteries according to claim 15, further comprising the step of comparing the voltage of the even-numbered battery with a reference voltage during the second half cycle.