Current balancing device for parallel battery cells in an electrified vehicle

Patent metadata

Field	Value
Publication number	US-9685796-B2
Application number	US-201514714878-A
Country	US
Kind code	B2
Filing date	May 18, 2015
Priority date	May 18, 2015
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

A current equalizer is provided for first and second battery elements connected in parallel to supply a DC link. A first constant resistance carries a first current from the first battery element to the DC link. A first variable resistance is connected in parallel with the first constant resistance. A second constant resistance carries a second current from the second battery element to the DC link. A second variable resistance is connected in parallel with the second constant resistance. A balancer inversely adjusts the first and second variable resistances in response to relative magnitudes of the first and second currents. As a result, the total currents supplied from each battery element to the DC link are equalized because the effective total resistance in series with each battery element compensates for the difference in the internal battery resistances.

First claim

What is claimed is:

1. A current equalizer for first and second battery elements connected in parallel to supply a DC link, comprising:
a first constant resistance to carry a first current from the first battery element to the DC link;
a first variable resistance connected in parallel with the first constant resistance;
a second constant resistance to carry a second current from the second battery element to the DC link;
a second variable resistance connected in parallel with the second constant resistance;
a balancer inversely adjusting the first and second variable resistances in response to relative magnitudes of the first and second currents.

2. The equalizer of claim 1 wherein the balancer is comprised of a movable magnet exposed to magnetic fields induced by the first and second currents.

3. The equalizer of claim 2 wherein the magnet is comprised of a permanent magnet.

4. The equalizer of claim 2 wherein the balancer is further comprised of first and second magnetic cores with central openings through which the first and second currents pass, respectively, and wherein each core includes a gap exposing the movable magnet to the induced magnetic fields.

5. The equalizer of claim 2 wherein the first and second variable resistances are comprised of a potentiometer, wherein the potentiometer includes first and second end terminals connected to opposite ends of a resistive track, wherein the potentiometer further includes a tap terminal connected to a slider that is movable along the resistive track, and wherein the slider is mechanically coupled to the movable magnet for moving therewith.

6. The equalizer of claim 5 further comprising a biaser creating a bias force tending to return the slider to a zero position.

7. The equalizer of claim 1 wherein the first and second constant resistances are comprised of intrinsic resistances of first and second power cables coupling the first and second battery elements to the DC link.

8. The equalizer of claim 1 wherein the first and second constant resistances include discrete resistors connected in series with first and second power cables coupling the first and second battery elements to the DC link.

9. The equalizer of claim 1 for first, second, third, and fourth battery elements connected in parallel, comprising a hierarchy of balancers.

10. A current balancing method, comprising:
coupling two parallel battery elements to a DC link via respective power cables carrying first and second currents;
applying magnetic fields induced by the currents to generate a net torque on a rotatable magnet; and
moving a potentiometer wiper linked to the rotatable magnet to inversely vary respective variable resistances connected in parallel with the respective power cables so that the battery elements deliver total currents that are equalized.

11. The method of claim 10 further comprising:
applying a bias force to the wiper tending to return the wiper to a zero position where the variable resistances are equal.

12. The method of claim 10 further comprising:
concentrating the induced magnetic fields in first and second magnetic cores with central openings through which the first and second currents pass, respectively, and wherein each core includes a gap exposing the magnet balance to the concentrated magnetic fields.

13. An electric drive system for a transportation vehicle, comprising:
first and second battery strings each comprised of series-connected battery cells;
first and second power cables coupling the first and second battery strings together in parallel and to a DC link, wherein first and second constant resistances are present within the first and second power cables which carry first and second currents to the DC link, respectively;
a first variable resistance connected in parallel with the first constant resistance;
a second variable resistance connected in parallel with the second constant resistance; and
a balancer inversely adjusting the first and second variable resistances in response to relative magnitudes of the first and second currents.

14. The electric drive system of claim 13 wherein the balancer is comprised of a movable magnet exposed to magnetic fields induced by the first and second currents.

15. The electric drive system of claim 14 wherein the magnet is comprised of a permanent magnet.

16. The electric drive system of claim 14 wherein the balancer is further comprised of first and second magnetic cores with central openings through which the first and second currents pass, respectively, and wherein each core includes a gap exposing the movable magnet to the induced magnetic fields.

17. The electric drive system of claim 14 wherein the first and second variable resistances are comprised of a potentiometer, wherein the potentiometer includes first and second end terminals connected to opposite ends of a resistive track, wherein the potentiometer further includes a tap terminal connected to a slider that is movable along the resistive track, and wherein the slider is mechanically coupled to the movable magnet for moving therewith.

18. The electric drive system of claim 17 further comprising a biaser creating a bias force tending to return the slider to a zero position.

19. The electric drive system of claim 13 wherein the first and second constant resistances are comprised of intrinsic resistances of the first and second power cables, respectively.

20. The electric drive system of claim 13 wherein the first and second constant resistances include discrete resistors connected in series with the first and second power cables, respectively.

Assignees

• Ford Global Tech Llc

Inventors

• Poirier Eric

Classifications

• H02J7/52 Primary

  for charge balancing, e.g. equalisation of charge between batteries · CPC title

• H02J7/0014 Primary

  Electricity · mapped topic

• H02J7/34

  Parallel operation in networks using both storage and other DC sources, e.g. providing buffering (H02J7/14 takes precedence) · CPC title

• B60L11/1866

  Operations & Transport · mapped topic

• Y02E60/10

  Energy storage using batteries · CPC title