Battery performance monitor

• US 20090027056A1
• Filed: 02/19/2008
• Published: 01/29/2009
• Est. Priority Date: 07/23/2007
• Status: Active Grant

• Current Assignee: Battery Technology Holdings LLC
• Original Assignee: Andrew F Kallfelz, Yung-Sheng Huang
• Inventors: Huang, Yung-Sheng, Kallfelz, Andrew F.
• Granted Patent: US 7,928,735 B2
• Time in Patent Office: Days
• US Class Current: 324/439
• CPC Class Codes: B60L 2250/10 by alarm
• CPC Class Codes: B60L 2260/46 by self learning
• CPC Class Codes: B60L 2260/56 Temperature prediction, e.g. for pre-cooling
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: B60L 58/16 responding to battery ageing, e.g. to the number of charging cycles or the state of health [SoH]
• CPC Class Codes: G01R 31/364 Battery terminal connectors with integrated measuring arrangements
• CPC Class Codes: G01R 31/3647 for determining the ability of a battery to perform a critical function, e.g. cranking
• CPC Class Codes: G01R 31/371 with remote indication, e.g. on external chargers
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 90/16 Information or communication technologies improving the operation of electric vehicles

Abstract

Improvements both in the methods whereby existing techniques for determining the condition of a battery are communicated to a user (for example, to the owner of a private vehicle, or to the service manager of a fleet of vehicles), or the vehicle'"'"'s operating system, and in the methods for evaluating the condition of the battery are disclosed. It has been discovered by the inventors that the difference in internal resistance of a fully charged battery as measured during charging and as measured after charging is greater for a battery in poor condition than for a new battery. The invention relates in part to instruments and corresponding methods for evaluating the condition of a battery utilizing this discovery.

Claims

1. A method for determining the state of health of a battery, comprising the steps of:

applying charging current to the battery, until it is determined that the battery is substantially fully charged;

measuring the conductance Cc of the fully-charged battery while charging current is being applied;

discontinuing application of charging current to the battery;

measuring the conductance Cn of the fully-charged battery when charging current is no longer being applied; and

evaluating the state of health of the battery by comparing Cn to Cc.

2. The method of claim 1, comprising the further steps of monitoring one or both of the conductance or voltage of the battery during charging, and determining the battery to be substantially fully charged when the monitored conductance and/or voltage are substantially stable.

3. The method of claim 1, where said step of measuring the conductance Cn of the fully-charged battery when charging current is no longer being applied is performed after the battery has reached equilibrium after cessation of application of charging current.

4. In combination with the method of claim 1, a further method for additionally tracking the state of charge (SOC) of the battery, comprising the following additional steps:

(a) performing an initialization routine, comprising the steps of;

storing a value for the conductance Cn of the battery when fully charged, and taking this as its conductance at 100% SOC;

determining a value for conductance of the battery corresponding to 0% SOC;

monitoring flow of current into and out of the battery while monitoring the corresponding change in its conductance, to establish a scale factor therebetween; and

using said scale factor to determine the amount of current corresponding to discharge from 100% SOC to 0% SOC;

(b) thereafter tracking the SOC of the battery, recommencing each time the battery is determined to be fully-charged, by;

setting SOC of the fully-charged battery to 100%;

monitoring flow of current into and out of the battery;

integrating the flow of current over time; and

employing said scale factor to convert the integrated value for current flow to a corresponding value for SOC.

5. A method of tracking the state of charge (SOC) of a battery over a number of charge/discharge cycles, comprising the steps of:

(a) performing an initialization routine, comprising the steps of;

storing a value for the conductance Cn of the battery when fully charged, and taking this as its conductance at 100% SOC;

determining a value for conductance of the battery corresponding to 0% SOC;

monitoring flow of current into and out of the battery while monitoring the corresponding change in its conductance, to establish a scale factor therebetween; and

using said scale factor to determine the amount of current corresponding to discharge from 100% SOC to 0% SOC;

(b) thereafter monitoring the charging of the battery, to determine when the battery is fully charged; and

(c) tracking the SOC of the battery, recommencing each time the battery is determined to be fully-charged, by;

setting the SOC of the fully-charged battery to 100%;

monitoring flow of current into and out of the battery;

integrating the flow of current over time; and

employing said scale factor to convert the integrated value for current flow to a corresponding value for SOC.

6. The method of claim 5, further comprising evaluating the state of health (SOH) of the battery, by:

measuring its internal conductance C when the battery is fully charged, and while charging current is being applied, and storing the measured value as Cc;

measuring the internal conductance of the fully-charged battery after cessation of application of charging current, and storing the measured value as Cn; and

evaluating the state of health of the battery by comparing Cn to Cc.

7. The method of claim 6, wherein said step of measuring the internal conductance of the fully-charged battery after cessation of application of charging current is performed after the battery has reached equilibrium after cessation of application of charging current.

8. The method of claim 5, comprising the further steps of monitoring one or both of the conductance or voltage of the battery during charging, and determining the battery to be substantially fully charged when the monitored conductance and/or voltage are substantially stable.

9. A method for tracking the state of health and state of charge of a battery over time, comprising the following steps:

evaluating a parameter indicative of the capability of the battery at intervals, yielding a series of values Ca;

determining the maximum values reached in the series of values for Ca, and storing these as Ce;

determining the maximum value reached by Ce over the lifetime of the battery and storing it as Cm;

determining the state of health of the battery by comparing Ce and Cm; and

determining the state of charge of the battery by comparing Ca and Ce.

10. The method of claim 9, comprising the further step of predicting incipient battery failure by comparing Ce to a predetermined value Ceol.

11. The method of claim 10, wherein Ceol is set as a predetermined fraction of Cm.

12. The method of claim 9, comprising the further step of controlling charging of said battery by comparing Ca to a predetermined value Cdod for maximum permissible depth of discharge.

13. The method of claim 12, wherein Cdod is set as a predetermined fraction of Cm.

14. The method of claim 9 wherein said parameter indicative of the capability of the battery is its DC internal conductance.

15. The method of claim 9, wherein Ce is determined by performance of the following steps:

applying charging current to the battery, until it is determined that the battery is substantially fully charged;

discontinuing application of charging current to the battery;

measuring the conductance Cn of the fully-charged battery when charging current is no longer being applied, and when the battery has reached equilibrium after charging; and

setting Ce equal to Cn.

16. The method of claim 13, wherein said step of measuring the conductance Cn of the fully-charged battery when charging current is no longer being applied is performed when the battery has reached equilibrium after charging