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

• US 20010035738A1
• Filed: 02/22/2001
• Published: 11/01/2001
• Est. Priority Date: 02/23/2000
• Status: Active Grant

• Current Assignee: VB Autobatterie GmbH
• Original Assignee: VB Autobatterie GmbH
• Inventors: Ubermeier, Dieter, Meissner, Eberhard, Laig-Horstebrock, Helmut, Leiblein, Karl-Heinz, Brunn, Detief
• Granted Patent: US 6,392,415 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• 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 ti over time interval dt, b) 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, 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 (Ui, 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)

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, I_i represents current intensity and C represents capacitance, and

calculating the state of charge of the rechargeable battery from the no load voltage obtained from 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)

U_i=Uo+R*I_i+[a*i_o*arc sin h(I_i/i_o)−

a*I_i]+1/C∫

Idt 

 

(2)

and measured values U(t_i) is minimized, wherein Uo, R, I_i and C are the same, i_o is current intensity, and a represents resistance.

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)

dUo/dq=(Uo(t_n)−

Uo(t<sub>n−

1</sub>))/(q(t_n)−

q(t<sub>n−

1</sub>))<

Dgr 

 

(3)

are used, wherein the limit Dgr per cell is selected from the range 6V/Qo to −

6V/Qo, and Qo is capacity of the battery.

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⁺, or 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.