State of Charge Quality Based Cell Balancing Control

• US 20150231985A1
• Filed: 02/20/2014
• Published: 08/20/2015
• Est. Priority Date: 02/20/2014
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Li, Yonghua
• Granted Patent: US 9,381,825 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2260/46 by self learning
• CPC Class Codes: B60L 58/13 Maintaining the SoC within a determined range
• CPC Class Codes: B60L 58/22 Balancing the charge of battery modules
• CPC Class Codes: G01R 31/36 Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: H02J 2310/48 for electric vehicles [EV] or hybrid vehicles [HEV]
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0019 using switched or multiplexed charge circuits
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

Hybrid-electric and pure electric vehicles include a traction battery comprised of many cells. During repeated charge and discharge cycles, the state of charge of the cells may vary from cell to cell. To optimize traction battery usage, it is desirable that the state of charge of the cells be equalized. Cell balancing can equalize the states of charge and improve battery performance. To achieve proper cell balancing, an accurate state of charge value should be known for each cell. An accurate state of charge value may be achieved when a persistent excitation condition and an estimation convergence condition are met. If the conditions are not met, active excitation of the battery may be performed to improve the chances of meeting the conditions. Cell balancing may be initiated and terminated according to state of charge values estimated when the conditions are satisfied.

Claims

1. A battery control system comprising:

a traction battery including a plurality of cells; and

at least one controller programmed to generate model parameter estimates for the cells and, in response to a magnitude of a state of charge difference between cells being greater than a predetermined value while a persistent excitation condition and an estimation convergence condition are satisfied, balance the cells according to states of charge derived from the model parameter estimates.

2. The battery control system of claim 1 wherein the persistent excitation condition is satisfied when

3. The battery control system of claim 1 wherein the estimation convergence condition is satisfied when an error magnitude between at least one of the model parameter estimates and a corresponding measured model parameter value is less than a predetermined threshold for a predetermined period of time.

4. The battery control system of claim 1 wherein the at least one controller is further programmed to, in response to at least one of the persistent excitation condition and the estimation convergence condition not being satisfied, cause a predetermined number of frequency component amplitudes of battery power demand to exceed a predetermined magnitude without affecting vehicle acceleration.

5. A vehicle comprising:

a traction battery including a plurality of cells; and

at least one controller programmed to, in response to a magnitude of a state of charge difference between cells being greater than a predetermined value while a persistent excitation condition and an estimation convergence condition are satisfied, balance the cells according to states of charge derived from estimated cell model parameters.

6. The vehicle of claim 5 wherein the persistent excitation condition is satisfied when

7. The vehicle of claim 5 wherein the estimation convergence condition is satisfied when an error magnitude between at least one estimated traction battery parameter and a corresponding measured traction battery parameter value is less than a predetermined threshold for a predetermined period of time.

8. The vehicle of claim 5 wherein the at least one controller is further programmed to, in response to the magnitude of the state of charge difference between cells being less than the predetermined value, terminate balancing the cells.

9. The vehicle of claim 5 wherein the at least one controller is further programmed to, in response to the magnitude of the state of charge difference between cells being less than the predetermined value while the persistent excitation condition and the estimation convergence condition are satisfied during cell balancing, terminate balancing the cells.

10. The vehicle of claim 5 wherein the at least one controller is further programmed to, in response to the persistent excitation condition and the estimation convergence condition not being satisfied for a predetermined period of time after starting cell balancing, cause a predetermined number of frequency component amplitudes of battery power demand to exceed a predetermined magnitude without affecting acceleration of the vehicle.

11. The vehicle of claim 5 wherein the at least one controller is further programmed to balance the cells at a scheduled time in response to the magnitude of the state of charge difference between the cells being greater than the predetermined value while the persistent excitation condition and the estimation convergence condition are satisfied at the scheduled time.

12. The vehicle of claim 11 wherein the at least one controller is further programmed to, in response to the persistent excitation condition and the estimation convergence condition not being satisfied at the scheduled time, cause a predetermined number of frequency component amplitudes of battery power demand to exceed a predetermined magnitude without affecting acceleration of the vehicle.

13. A method of balancing cells of a traction battery by at least one controller comprising:

initiating, after learning a first set of states of charge for the cells in response to a persistent excitation condition and an estimation convergence condition being satisfied, cell balancing based on first state of charge differences between the cells having a magnitude greater than a predetermined value; and

terminating, after learning a second set of states of charge for the cells in response to the persistent excitation condition and the estimation convergence condition being satisfied, cell balancing based on second state of charge differences between the cells having a magnitude less than the predetermined value.

14. The method of claim 13 wherein the persistent excitation condition is satisfied when

15. The method of claim 13 wherein the estimation convergence condition is satisfied when an error magnitude between an estimated model parameter and a corresponding measured model parameter value is less than a predetermined threshold for a predetermined period of time.

16. The method of claim 13 further comprising permitting cell balancing to be initiated at a predetermined time.

17. The method of claim 16 further comprising causing a predetermined number of frequency component amplitudes of battery power demand to exceed a predetermined magnitude without affecting vehicle acceleration in response to the persistent excitation condition and the estimation convergence condition not being satisfied within a predetermined time interval before the predetermined time.

18. The method of claim 13 further comprising causing a predetermined number of frequency component amplitudes of battery power demand to exceed a predetermined magnitude without affecting vehicle acceleration in response to cell balancing not terminating a predetermined amount of time after being initiated.

19. The method of claim 13 further comprising limiting a number of cell balancing cycles within a single ignition cycle to be less than a predetermined number of cycles.