POWER AND CURRENT ESTIMATION FOR BATTERIES

• US 20160131714A1
• Filed: 11/04/2015
• Published: 05/12/2016
• Est. Priority Date: 11/07/2014
• Status: Active Grant

• Current Assignee: Volvo Car Corporation (AB Volvo)
• Original Assignee: Volvo Car Corporation (AB Volvo)
• Inventors: WIK, Torsten, KUUSISTO, Hannes, FRIDHOLM, Bjorn
• Granted Patent: US 10,330,731 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• 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: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 2010/4271 Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
• CPC Class Codes: H01M 2220/20 Batteries in motive systems, e.g. vehicle, ship, plane
• 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

A method and a system are provided for determining a maximum charge current or a maximum discharge current of an energy storage cell of an energy storage device. The method includes providing a predetermined upper voltage limit or lower voltage limit, and providing a time horizon as a time difference from a present time to a future time. The method also include, with a repetition time period different from the time horizon, repeating measuring a present voltage level of the energy storage cell, calculating a voltage difference between the present voltage level and the upper voltage limit or the lower voltage limit, and determining the maximum charge current or maximum discharge current corresponding to the voltage difference and a model, such that the estimated voltage is within the voltage limits.

Claims

1. A method for determining a maximum electrical charge current or a maximum electrical discharge current of an energy storage cell, the method comprising:

(a) providing a predetermined upper voltage limit or lower voltage limit of the energy storage cell;

(b) providing a time horizon as a time difference from a present time to a future time;

wherein, with a repetition time period different from the time horizon,

repeating the following steps;

(c) measuring a present voltage level of the energy storage cell;

(d) calculating, by a control unit, a voltage difference between the present voltage level and the upper voltage limit or the lower voltage limit; and

(e) based on the voltage difference, the time horizon, and an equivalent circuit model comprising a capacitance and a resistance of the energy storage cell relating an electrical charge current or an electrical discharge current to a respective estimated voltage of the energy storage cell, determining, by the control unit, the maximum electrical charge current or maximum electrical discharge current of the energy storage cell corresponding to the voltage difference,

wherein the respective estimated voltage of the energy storage cell is less than or equal to the upper voltage limit during the time horizon in the case of an electrical charge current, or larger than or equal to the lower voltage limit during the time horizon in the case of an electrical discharge current.

2. The method according to claim 1 wherein the repetition time period is shorter than the time horizon.

3. The method according to claim 1 wherein the repetition time period and the time horizon overlaps in time.

4. The method according to claim 1 wherein the maximum electrical charging current or maximum electrical discharge current is assumed to be constant in magnitude for the entire time horizon when predicting the estimated voltage from the model of the energy storage cell.

5. The method according to claim 1 wherein the maximum electrical charge current or maximum electrical discharge current (i_max;

i_min) is given by;

6. The method according to claim 1 wherein the maximum electrical charge current or maximum electrical discharge current (i_max;

i_min) is given by;

7. The method according to claim 1 wherein the maximum electrical charge current or maximum electrical discharge current is further based on a model comprising a convergence factor, wherein a magnitude of the maximum electrical charge current or maximum electrical discharge current depends on the magnitude of the convergence factor.

8. The method according to claim 1 wherein the energy storage cell and a controller is modeled as a feedback control system, wherein the energy storage cell is modeled as a transfer function (G) from change in charge current or change in discharge current to a change in voltage given by:

9. The method according to claim 8 wherein the controller is a PI-controller with a second transfer function (F) given by:

10. The method according to claim 9, wherein the convergence factor (γ

) is larger than zero, and wherein, with the convergence factor, the controller F(s) is given by;

11. The method according to claim 1 for controlling an electrical charge current or electrical discharge current of an energy storage cell further comprising:

receiving a request for a demanded electrical charge current or a demanded electrical discharge current from the energy storage cell;

wherein, if the demanded electrical charge current is larger than the maximum electrical charge current,

controlling the energy storage cell to provide the maximum electrical charge current,

or, wherein, if the demanded electrical discharge current is larger than the maximum electrical discharge current, control the energy storage cell to provide the maximum electrical discharge current.

12. A system for determining a maximum electrical charge current or a maximum electrical discharge current of an energy storage cell, the system comprising:

a control unit; and

a voltage measuring device;

wherein the control unit is configured to;

(a) receive a predetermined upper voltage limit or lower voltage limit of the energy storage cell;

wherein, with a repetition time period different from a predetermined time horizon being a time difference from a present time to a future time, the control unit is configured to repeat the following;

(b) receive, from the voltage measuring device, a measurement of a present voltage level of the energy storage cell;

(c) calculate a voltage difference between the present voltage level and the upper voltage limit or the lower voltage limit;

(d) based on the voltage difference, the time horizon, and an equivalent circuit model comprising a capacitance and a resistance of the energy storage cell relating an electrical charge current or an electrical discharge current to a respective estimated voltage of the energy storage cell, determine the maximum electrical charge current or maximum electrical discharge current of the energy storage cell corresponding to the voltage difference,

wherein the respective estimated voltage of the energy storage cell is less than or equal to the upper voltage limit during the time horizon in the case of an electrical charge current, or larger than or equal to the lower voltage limit during the time horizon in the case of an electrical discharge current.

13. The system according to claim 12 wherein the control unit is partially configured as a feedback controller with integral action such that if the demanded current is larger than the maximum electrical charge current or the maximum electrical discharge current, the applied current can be determined as the output of a feedback controller, with integral action, and having the voltage difference as reference input.

14. The system according to claim 13 wherein the controller is a PI-controller with a transfer function (F) given by:

15. The system according to claim 12 arranged in a vehicle.