Battery state of charge sensing system

• US 5,761,072 A
• Filed: 11/08/1995
• Issued: 06/02/1998
• Est. Priority Date: 11/08/1995
• Status: Expired due to Fees

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Bardsley, David John Jr., Song, Jing
• Primary Examiner(s): Stamber, Eric W.
• Application Number:
  US08/555,572
• Time in Patent Office: 937 Days
• Field of Search: 364/483, 364/492, 364/550, 364/481, 395/750, 340/636, 324/426, 324/427, 324/428, 320/13, 320/20, 320/39, 320/43, 320/44, 320/48
• US Class Current: 702/63
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3832 without measurement of battery voltage

Abstract

A microprocessor samples the net effective current from a battery several times a second. A fast average current I_f is calculated using an IIR filter on the net average current. A slow average current I is calculated by integrating the net average current over time with respect to time. An Ampere Hour Capacity is calculated by the use of the Peukert equation, which is split into two terms. A first capacity term is calculated using the fast average current I_f and a slow capacity term is calculated using the slow average current I. The slow capacity term is then multiplied by a weighting constant C₂ and summed with the fast capacity term which is multiplied by (1-C₂).

Claims

1. A method for computing the capacity for a storage battery, comprising the steps of:

measuring the net discharge current I for the operating battery,

calculating a fast average current I_f using the equation ##EQU10## where C₁ is a constant matched with the battery characteristics, calculating a slow average current I using the equation ##EQU11## and calculating the Ampere Hour Capacity using the equation

space="preserve" listing-type="equation">Ampere Hour Capacity=C.sub.2 * P.sub.1 (I).sup.-P.sbsp.2 +(1-C.sub.2)* P.sub.1 (I.sub.f).sup.-P.sbsp.2

where P₁ and P₂ are Peukert constants, and C₂ is a weighting constant, determined to match the operating characteristics of the battery being measured.

2. The method as described in claim 1 wherein the fast average current I_f is calculated by using an IIR filter on the value of the net discharge current I.

3. The method as described in claim 1 wherein the fast average current I_f is calculated over a time period as short as 5 seconds to as long as 30 seconds.

4. The method as described in claim 3 wherein the slow average current I is calculated for an effective time period at least 10 times longer than the time period for calculating the fast average current I_f.

5. The method as described in claim 4 wherein the slow average current I is calculated for an effective time period of at least 30 minutes.

6. The method as described in claim 4 wherein the slow average current I is calculated for an effective time period defined from approximately key on to key off for an electrically powered vehicle in which the battery is used for storing electrical energy.

7. A method for computing the Ampere Hour Capacity for a storage battery of the type used as an energy source for the propulsion system of an electric vehicle, comprising the steps of:

measuring the net discharge current I for the operating battery,

calculating a fast average current I_f using the equation ##EQU12## where C₁ is a constant matched with the battery characteristics, with the fast average current I_f being calculated over a time period from as short as 5 seconds to as long as 60 seconds,

calculating a slow average current I using the equation ##EQU13## with the slow average current I calculated for an effective time period of at least 100 times longer than the time period for calculating the fast average current I_f, and

calculating the Ampere Hour Capacity using the equation

space="preserve" listing-type="equation">Ampere Hour Capacity=C.sub.2 *P.sub.1 (I).sup.-P.sbsp.2 +(1-C.sub.2)*P.sub.1 (I.sub.f).sup.-P.sbsp.2

where P₁ and P₂ are Peukert constants and C₂ is a weighting constant determined to match the operating characteristics of the battery being measured.

8. The method as described in claim 7 wherein the slow average current I is calculated for an effective time period defined from approximately key on to key off for an electrically powered vehicle.

9. A method for calculating the State of Charge (SOC) for a storage battery used as an energy source for the propulsion system of an electric vehicle, comprising the steps of:

measuring the net discharge current I for the operating battery,

calculating a fast average current I_f using the equation ##EQU14## where C₁ is a constant matched with the battery characteristics, calculating a slow average current I using the equation ##EQU15## and calculating the Ampere Hour Capacity using the equation

space="preserve" listing-type="equation">Ampere Hour Capacity=C.sub.2 *P.sub.1 (I).sup.-P.sbsp.2 +(1-C.sub.2)*P.sub.1 (I.sub.f).sup.-P.sbsp.2

where P₁ and P₂ are Peukert constants and C₂ is a weighting constant determined to match the operating characteristics of the battery being measured,

measuring the Ampere Hours Consumed from the net discharge current I for the battery, and

calculating the State of Charge (SOC) using the equation ##EQU16##

10. The method as described in claim 9 wherein the fast average current I_f is calculated over a time period as short as 5 seconds to as long as 30 seconds.

11. The method as described in claim 10 wherein the slow average current I is calculated for an effective time period at least 10 times longer than the time period for calculating the fast average current I_f.

12. The method as described in claim 10 wherein the slow average current I is calculated for an effective time period of at least 30 minutes.

13. The method as described in claim 10 wherein the slow average current I is calculated for an effective time period defined from approximately key on to key off for an electrically powered vehicle in which the battery is used for storing electrical energy.

14. The method as described in claim 9 wherein the fast average current I_f is calculated by using an IIR filter on the value of the net discharge current I.