Battery capacity calculation method

• US 5,847,566 A
• Filed: 06/07/1995
• Issued: 12/08/1998
• Est. Priority Date: 09/16/1994
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Yamazaki, Toshihiko, Marritt, William A.
• Primary Examiner(s): Nguyen, Vinh P.
• Assistant Examiner(s): VALONE, THOMAS F
• Application Number:
  US08/472,420
• Time in Patent Office: 1,280 Days
• Field of Search: 324/427, 364/481, 364/483, 320/48, 320/44
• US Class Current: 324/427
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/3835 involving only voltage measurements

Abstract

A battery capacity meter and a method for precisely calculating a battery capacity are obtained by measuring a terminal voltage of the battery and sequentially calculating the measured terminal voltages. In a battery capacity meter of the present invention, a calculation process is carried out. After a power source is connected to the battery capacity meter, an initial value S₀ under non-consistent charge state S_i is calculated from an initial value V₀ of a terminal voltage V_i. Next, V_i and S_i are related to a current I_i, and an equation for relating a variation amount ΔS_i of S_i to S_i is formed. Under this relationship, ΔS_i is obtained from V_i and S_i in a time interval Δt. A value of S_i is updated. Either a remaining capacity or a fuel-gauge normalized remaining capacity are obtained from the updated value of S_i. A process operation is returned to a step where ΔS_i is calculated, and this process is repeated.

Claims

1. A method for determining battery capacity comprising the steps of:

a) measuring an initial value V₀ of a terminal voltage of a battery to obtain an initial state of charge condition value S₀ of an indication value S indicative of a state of charge condition of the battery, in which S is defined to be equal to 0 when the battery is fully charged and is defined to be equal to 1 when the battery is effectively discharged;

b) determining a subsequent value V_i of a terminal voltage after a time interval Δ

t and estimating a discharge current value I based on the determined subsequent value V_i ;

c) calculating a change Δ

S₀ in the initial value state of charge condition S₀ of the battery over the time interval Δ

t as a function of the discharge current value I and the initial state of charge condition indication value S₀ using the following equation;

space="preserve" listing-type="equation">Δ

S.sub.0 =I.sub.i ×

Δ

t×

f(I.sub.i, S.sub.0)÷

M

wherein an average battery discharge current corresponding to said discharge current value I is I_i, where f(I_i,S₀) is a function such that when S₀ =0 f(I_i,S₀)=×

1;

when S₀ =1, f(I_i,S₀)=1 if I_i is low, f(I_i S₀)=(I_i ÷

I₀)^Y if I_i is high, and f(I_i,S₀) increases monotonically when S₀ is increased from 0 to 1; and

M, I₀, and Y are constants depending on the battery;

d) updating the state of charge condition by calculating a current state of charge condition value S_i of the indication value S, wherein S_i =S₀ +Δ

S₀ ;

e) repeating step b;

f) calculating a change Δ

S_i in the current state of charge condition value S_i of the battery over the time interval Δ

t as a function of the discharge current value I_i and the state of charge condition indication value S_i using the following equation;

space="preserve" listing-type="equation">Δ

S.sub.i =I.sub.i ×

Δ

t×

f(I.sub.i, S.sub.i)÷

M

wherein f(I_i,S_i) is a function such that when S_i =0, f(I_i,S_i)=1;

when S_i =1, f(I_i S_i)=1 if I_i is low, f(I_i S_i)=(I_i ÷

I₀)^Y if I_i is high, and f(I_i,S_i) increases monotonically when S_i is increased from 0 to 1; and

M, I₀, and Y are constants depending on the battery; and

g) updating the state of charge condition by calculating a new value S_i+1 of the indication value S indicative of a new state of charge condition of the battery from the equation;

space="preserve" listing-type="equation">S.sub.i+1 =S.sub.i +Δ

S.sub.i.

2. The method of claim 1, wherein at said step a), said initial state of charge condition value S₀ of an indication value S indicative of the state of charge condition of said battery is calculated by employing the following equation:

space="preserve" listing-type="equation">S.sub.0 =K.sub.0 +K.sub.1 V.sub.0.sup.1 +K.sub.2 V.sub.0.sup.2 +. . . +K.sub.n V.sub.0.sup.n,

where symbols K₀ , K₁, K₂, . . . , K_n are constants depending on the battery.

3. The method of claim 1, wherein data representing a correspondence table among said indication value S_i, said terminal voltage V_i, and said variation amount S_Qi are previously stored in a memory, and wherein said variation amount Δ

S_i is calculated from said data at said step f).

4. The method of claim 1, further comprising:

calculating an index value of said battery capacity based upon the following equation;

space="preserve" listing-type="equation">capacity=(1-S.sub.i+1)xn,

where n is an arbitrary real number.

5. The method of claim 1, further comprising:

performing a correction process to said indication value S_i+1 so that a corrected value of said indication value is substantially proportional to a representative output value of a device powered by said battery.

6. The method of claim 5, wherein said correction process performing step comprises calculating a linearized index of said battery capacity by employing the following equation:

space="preserve" listing-type="equation">capacity={1-h(S.sub.i+1)}xn,

where symbol n indicates an arbitrary real number, and h(S) is a function such that when S is increased from 0 to 1, this function increases monotonically;

when S=0, h(S)=0;

when S=1;

h(S)=1; and

when S=1/2, 1/2<

h(S)<

3^1/2 /2.

7. The method of claim 1, wherein in at least one of said steps a), b), and c) data representing a correspondence table between said used data and the calculation results are previously stored in a memory, and a process operation is carried out based on said data.

8. The method of claim 1, wherein at said step b), said subsequent value of the terminal voltage V_i is sequentially measured at every time interval Δ

t, and the average battery discharge current I_i at a time interval Δ

t is calculated by the following equation;

space="preserve" listing-type="equation"> I.sub.i ={A-B×

(Q.sub.i -Q.sub.ZONE1)-C×

(Q.sub.i -Q.sub.ZONE2) .sup.2 -V.sub.i }+R!I.sub.i ={A-B×

(S.sub.i -S.sub.ZONE1)-C×

(S.sub.i -S.sub.ZONE2).sup.2 -V.sub.i }÷

R,

where symbols A, B, C, R, S_ZONE1, S_ZONE2 are constants dependent on the battery, 0≦

S_ZONE1 ≦

0.99, S_ZONE1 ≦

S_ZONE2 ≦

0.99, 0≦

S-S_ZONE1,0≦

S_ZONE2, and S_i is an indication value representative of the current battery state of charge condition.