Battery state-of-charge management method

• US 8,635,037 B2
• Filed: 10/19/2010
• Issued: 01/21/2014
• Est. Priority Date: 10/19/2009
• Status: Active Grant

• Current Assignee: Nuvera Fuel Cells, Inc. (Nacco Industries Incorporated)
• Original Assignee: Nuvera Fuel Cells, Inc. (Nacco Industries Incorporated)
• Inventors: Quet, Pierre-Francois
• Primary Examiner(s): Taningco, Alexander H
• Assistant Examiner(s): Perez Bermudez, Yaritza H
• Application Number:
  US12/907,902
• Publication Number:
  US 20110093223A1
• Time in Patent Office: 1,190 Days
• Field of Search: 702/60, 702/63, 320/101, 320/104, 320/132, 324/427
• US Class Current: 702/63
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 16/006 of fuel cells with rechargeable batteries
• CPC Class Codes: H01M 8/04656 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/0491 of fuel cell stacks
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

Equipment and methods for estimating and regulating the state of charge (SOC) of a battery in a hybrid fuel cell-battery system for use in a moving vehicle. The SOC is continuously estimated and the fuel cell power is regulated to maintain the SOC at a level such that the battery has enough stored energy to operate motors used in the vehicle, and enough spare capacity to accept regenerative energy from these motors during further operations.

Claims

1. A method of managing a state of charge of a battery in a hybrid electric power system comprising a fuel cell, the method comprising:

defining a setpoint;

calculating an estimated present state of charge of the battery according to the following equation;

2. The method according to claim 1, wherein the regulation of the state of charge of the battery effectively regulates the state of charge of the battery to within a selected range.

3. The method according to claim 2, wherein the regulation of the state of charge of the battery effectively regulates the state of charge of the battery to within 5% of the setpoint.

4. The method according to claim 1, wherein regulation of the state of charge of the battery effectively regulates the state of charge of the battery to the setpoint.

5. The method according to claim 1, wherein the state of charge of the battery is regulated by a control technique chosen from proportional control, proportional-integral control, proportional-integral-derivative control, and linear quadratic control.

6. The method of claim 1, wherein the fuel cell current is set to a value defined by the following equation:

I_FC(k)=(SOC_SP−

(k))*K_{SOC reg}

where I_FC(k) is the fuel cell current, SOC_SP is the setpoint, (k) is the estimated present state of charge of the battery and K_{SOC reg} is a control gain.

7. The method of claim 6, wherein the control gain, K_{SOC reg}, is defined according to the following equation:

8. The method of claim 7, wherein the calculated fuel cell current is coerced between a minimum fuel cell current value and a maximum fuel cell current value.

9. The method of claim 1, wherein the observer gain is calculated using a method chosen from pole placement or Kalman filtering.

10. The method according to claim 1, further comprising coercing the calculated estimated present state of charge of the battery to a value between 0 and 1.

11. The method according to claim 1, wherein the state of charge of the battery is regulated by placing the fuel cell system in idle when the estimated present state of charge of the battery is greater than a threshold high state of charge value.

12. The method according to claim 11, further comprising monitoring an electric load that draws power from the battery while the system is in idle and restarting the fuel cell system when an electric load that draws power from the battery at or above a threshold value is detected.

13. The method according to claim 1, wherein the battery current is measured directly.

14. The method according to claim 1, wherein the battery current is calculated.

15. The method according to claim 1, wherein the battery voltage is measured directly.

16. The method according to claim 1, wherein the battery voltage is sensed by a DC/DC converter connected in series with the fuel cell.

17. The method according to claim 1, wherein the estimated battery voltage {circumflex over (V)}_bus(k) is defined according to the following equation

{circumflex over (V)}_bus(k)=V_oc−

V_drop

where V_oc is an open circuit voltage of the battery;

V_drop is the voltage drop caused by the battery current due to the battery impedance.

18. The method according to claim 17, wherein the voltage drop caused by the battery current due to the battery impedance V_drop is defined according to the following equation:

V_drop=R_SeriesI_battery(k)

where R_Series is a resistance value chosen to model the impedance of the battery.

19. The method according to claim 1, wherein the battery capacity C_c is defined according to the following equation when I_battery(k) is greater than or equal to zero:

C_c=3600*Battery amp hour rating*e<sup>−

Discharging coeff*Ibattery(k)</sup>

and C_c is calculated according to the following equation when I_battery(k) is less than zero;

C_c=3600*(Battery amp hour rating−

Charging coeff*I_battery(k)).

where the Battery amp hour rating, the Discharging coeff, and the Charging coeff are constants associated with the battery.

20. The method according to claim 17, wherein the open circuit voltage of the battery is calculated according to the following equation:

V_oc=V_ocSlope*(k−

1)+V_ocOffset,

where V_ocSlope and V_ocoffset are both constants associated with the battery.