Method and apparatus for measuring the state-of-charge of a battery system

• US 5,381,096 A
• Filed: 10/05/1993
• Issued: 01/10/1995
• Est. Priority Date: 04/09/1992
• Status: Expired due to Fees

• Current Assignee: Edgar A. Hirzel
• Original Assignee: Edgar A. Hirzel
• Inventors: Hirzel, Edgar A.
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/132,160
• Time in Patent Office: 462 Days
• Field of Search: 324/426, 324/427, 324/430, 324/433, 364/481-483, 364/578, 364/150, 364/151, 320/48
• US Class Current: 324/427
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

A method and apparatus for measuring the state-of-charge of a battery is provided, which includes a metering system to communicate the state-of-charge to an operator of a device powered by the battery. A digital electronic model is provided to compute the instantaneous charge in a storage battery that tracks the actual terminal voltage of the battery. In the digital model, the battery model is expressed as a computer program. The electronic model derives from the measurement of the actual terminal voltage of an operating battery an internal voltage corresponding to the open circuit voltage of the battery. This internal voltage, representative of the state-of-charge of the battery, is communicated to an operator through a display.

Claims

1. A system coupled to a battery for measuring the state-of-charge of the battery while a device attached to said battery is operating, comprising:

a battery;

means for measuring the actual terminal voltage of the battery during operation of the device;

means for simulating at least some of the internal electrical characteristics of the battery, said means for simulating including;

circuit means for simulating the internal impedance of the battery with respect to time, said circuit means including capacitance means for simulating the internal capacitance of the battery; and

means responsive to a function of the simulated internal impedance for simulating the terminal voltage of the battery;

means for equating the simulated terminal voltage to said measured actual terminal voltage of the battery; and

means for developing a signal representing the state-of-charge of the battery in response to the voltage across said simulated internal capacitance of the battery.

2. The system defined in claim 1, further comprising means responsive to said function of the voltage across said simulated internal capacitance of the battery for communicating the state-of-charge of the battery.

3. The system defined in claim 1, wherein the means for equating comprises an operational amplifier.

10. The system defined in claim 1, wherein the means for simulating at least some of the internal electrical characteristics of the battery comprises a central processor unit.

4. A system coupled to a battery for measuring the state-of-charge of the battery while a device attached to said battery is operating, comprising:

a battery;

means for measuring the actual terminal voltage of the battery during the operation of the device;

means for modeling at least some of the internal electrical characteristics of the battery, said means for modeling including;

first means for modeling the internal impedance of the battery with respect to time, and for modeling the internal capacitance characteristics of the battery; and

second means responsive to the modeled internal impedance for modeling the terminal voltage of the battery;

means for equating the modeled terminal voltage to said measured actual terminal voltage of the battery; and

means for developing a signal representative the state-of-charge of the battery in response to the modeled internal capacitance characteristics of the battery.

5. The system defined in claim 4, further comprising means responsive to said function of the modeled internal capacitance characteristics of the battery for communicating the state-of-charge of the battery.

6. A system coupled to a battery for measuring the state-of-charge of the battery while a device attached to said battery is operating, comprising:

a battery;

a first circuit for measuring the actual terminal voltage of the battery during operation of the device;

an electronic circuit for simulating at least some of the internal electrical characteristics of the battery, said electronic circuit including;

a second circuit for simulating the internal impedance of the battery with respect to the time, said second circuit including a capacitor for simulating the internal capacitance of the battery; and

a third circuit responsive to the simulated internal impedance for simulating the terminal voltage of the battery;

an amplifier circuit, receiving as inputs the measured actual terminal voltage of the battery and the simulated terminal voltage of the battery, for equating the simulated terminal voltage to said measured actual terminal voltage of the battery; and

means for generating a signal representing the state-of-charge of the battery responsive to the voltage across said simulated internal capacitance of the battery.

7. The system defined in claim 6, further comprising a display responsive to voltage across said simulated internal capacitance of the battery for communicating the state-of-charge of the battery.

8. The system defined in claim 6, wherein the amplifier circuit comprises an operational amplifier.

11. The system defined in claim 6, wherein the electronic circuit comprises a central processor unit.

9. A method for measuring the state-of-charge of a battery attached to a device while said device is operating, comprising the steps of:

providing a battery;

measuring the actual terminal voltage of the battery during the operation of the device;

modeling the internal impedance and capacitance characteristics of the battery with respect to time;

modeling the terminal voltage of the battery responsive to the modeled internal impedance of the battery;

receiving the measured actual terminal voltage of the battery and equaling the modeled terminal voltage to said measured actual terminal voltage of the battery; and

communicating an output signal representing the state-of-charge of the battery as a function of the modeled internal capacitance characteristics of the battery.