Method for determining the state of charge of lead-acid rechargeable batteries

• US 6,392,415 B2
• Filed: 02/22/2001
• Issued: 05/21/2002
• Est. Priority Date: 02/23/2000
• Status: Expired due to Fees

• Current Assignee: VB Autobatterie GmbH
• Original Assignee: VB Autobatterie GmbH
• Inventors: Leiblein, Karl-Heinz, Brunn, Detief, Übermeier, Dieter, Laig-Hörstebrock, Helmut, Meissner, Eberhard
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/791,108
• Publication Number:
  US 20010035738A1
• Time in Patent Office: 453 Days
• Field of Search: 320/127, 320/128, 320/132, 320/135, 320/137, 320/DIG.21, 324/426, 324/427, 324/428, 324/433, 340/635, 340/636, 429/61, 429/90
• US Class Current: 324/433
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/3828 using current integration

Abstract

A method for determining the state of charge of lead-acid rechargeable batteries comprising a) substantially simultaneously measuring measured-value pairs (U_i, I_i) of the rechargeable battery voltage and current flowing at time t_i over time interval dt, b) selecting a group of said measured-value pairs (Ui, I_i) for which only a discharge current flowed in the last time interval dt, c) varying parameters Uo, R and C such that a residual sum of squares between values U_i given by formula (1)

U_i=Uo−R*I_i+1/C∫Idt  (1)

and measured values U(t_i) is minimized, wherein Uo represents no-load voltage, R represents resistance and C represents capacitance, and d) calculating the state of charge of the rechargeable battery from the no load voltage obtained from formula (1).

Claims

1. A method for determining the state of charge of lead-acid rechargeable batteries comprising:

substantially simultaneously measuring

a) measured-value pairs (U_i, I_i) of the rechargeable battery voltage and

b) current flowing at time t_i over time interval dt,

selecting a group of said measured-value pairs (U_i, I_i) for which only a discharge current flowed in the last time interval dt,

varying parameters Uo, R and C such that a residual sum of squares between values U_i given by formula (1)

2. The method as claimed in claim 1, wherein parameters Uo, R, a, i_o and C are varied such that a residual sum of squares between values U_i according to formula (2)

3. The method as claimed in claim 1, wherein selected Uo are compared with previous values in time, and wherein only values Uo which satisfy formula (3)

4. The method as claimed in claim 1, wherein the only measured value pairs (U_i, I_i) which are used are:

those in which I_i<

0 and for which the following condition has been satisfied since a last measured value with a positive current and a time interval dt with a positive contribution Q⁻

to the state of charge;

the magnitude of Q⁻

is either greater than the magnitude of Q⁺, the magnitude of Q⁻

is greater than about 2% of the battery capacity, where Q⁻

represents an (discharged) amount of charge which has been drawn since a last measurement point with a positive battery current in an uninterrupted discharge phase, and Q⁺ is an (charged) amount of charge which has been introduced in a latest uninterrupted (charging) phase with a positive battery current.

5. The method as claimed in claim 1, wherein measurement of data and switching on and off of loads are synchronized such that measured value pairs (U_i, I_i) with different current intensities I_i are obtained.

6. The method as claimed in claim 1, wherein switching on and off of loads is timed such that measured value pairs (U_i, I_i) with different current intensities I_i are obtained.

7. The method as claimed in claim 1, wherein the state of charge SOC (t_o) obtained at a selected time t_o is linked to general time t by other methods for determining the state of charge or by methods for determining change in the state of charge Δ

SOC (t_o,t) in a time from t_o to t, wherein Δ

SOC (t_o, t) is calculated from a converted amount of charge determined by integration of current flowing through the rechargeable battery.

8. The method as claimed in claim 1, wherein state of charge values SOC (t_i) obtained at different times t_i are linked by other methods for determining the state of charge values or by methods for determining the change in the state of charge Δ

SOC (t_i,t_i+1) in a time from t_i to t_i+1, and a present state of charge value SOC is determined by using a minimization method.

9. The method as claimed in claim 1, wherein voltage values Uo obtained are compared with a limit Uo-min, and undershooting is indicated and/or an action is taken.

10. The method as claimed in claim 1, wherein a limit Uo-min is selected such that it corresponds approximately to an equilibrium voltage of the rechargeable battery after its rated capacity has been drawn.