Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Reexamination Certificate
2001-02-27
2002-10-22
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
C320S116000
Reexamination Certificate
active
06469471
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for predicting and gauging the depth of available energy in a battery or electrochemical cell system. More particularly, although not exclusively, the present invention relates to methods and apparatus for measuring battery capacity, charge remaining and reserve time.
BACKGROUND TO THE INVENTION
It has long been recognised that battery or cell capacity depends on a number of factors. These include the batteries composition, geometry, discharge rate (i.e. load current), age, environmental temperature, end voltage, service history (i.e. characteristics of the batteries last charge), discharge depth and time on float. The available capacity of a battery can be represented as a complex, non-linear function of these parameters. The direct measurement of a number of these parameters to determine battery capacity is either impractical or financially prohibitive. One of the most well known techniques for measuring the capacity of a battery is known as a “discharge test” (IEEE Std
1188-1996
; “IEEE Recommended Practice for Maintenance, Testing, and Replacement of Valve
-
Regulated Lead
-
Acid
(
VRLA
)
Batteries for Stationary Applications
”). This procedure involves the full discharge of a battery into a stable load. A major disadvantage of this approach is that, in the context of the batteries application (for example in a telecommunication system), the system being powered is vulnerable to power outages as the battery must be disconnected from the system during its complete discharge. Further disadvantages include the necessity for bulky external loads, the need for backup power supplies and the labour involved in setting up and supervising the testing procedure.
Other techniques for measuring the battery capacity use methods whereby parameters such as impedance, (Gary J. Markle, “AC Impedance Testing for Valve Regulated Cell,”
INTELEC
1992, 9-4), conductance, (Michael E. Troy et al, “Midpoint Conductance Technology Used in Telecommunication Stationary Standby Battery Applications. Part VI. Considerations for Deployment of Midpoint Conductance in Telecommunications Power Applications,”
INTELEC
1997, 29-4), or internal resistance (Isamu Kurisawa and Masashi Iwata, “Internal Resistance and Deterioration of VRLA Battery—Analysis of Internal Resistance Obtained by Direct Current Measurement and its Application to VRLA Battery Monitoring Technique,”
INTELEC
1997, 29-3: Glenn Alber and Marco W. Migilaro, “Impedance Testing—s it a Substitute for Capacity Testing,”
INTELEC
1994, 10-1: Katsuhiko Yamamoto et al, “Deterioration Estimation Method for 200-Ah Sealed Lead-Acid Batteries,”
NTT Review
Vol. 7, No. 4, July 1995) are correlated with a capacity. These latter methods generally employ a composite model based on a number of parameters. This model usually incorporates reference to cell resistance or impedance in determining the battery capacity (Jean Paul Cun et al, “The Experience of a UPS Company in Advanced Battery Monitoring,”
INTELEC
1996, 22-5: Petrick K. Ng et al, “Evaluation of a Reverse Time Prediction Algorithm for Lead Acid Battery”,
INTELEC
1996, 616-21). These methods have generally been developed for off-line applications and require the use of specialised equipment. Although they have had some success, it is generally considered in the art that these techniques are best suited for identifying gross faults (Michael E. Troy et al, “Midpoint Conductance Technology Used in Telecommunication Stationary Standby Battery Applications. Part VI. Considerations for Deployment of Midpoint Conductance in Telecommunications Power Applications,”
INTELEC
1997, 29-4: Katsuhiko Yamamoto et al, “
Deterioration Estimation Method for
200-Ah Sealed Lead-Acid Batteries,”
NTT Review
VoL. 7, No. 4, July 1995), tracking battery age and making battery life time predictions (Gary J. Markle, “AC Impedance Testing for Valve Regulated Cell,”
INTELEC
1992, 9-4: Katsuhiko Yamamoto et al, “Deterioration Estimation Method for 200-Ah Sealed Lead-Acid Batteries,”
NTT Review
VoL. 7, No. 4, July 1995). A detailed short-term test of battery capacity measurement is still most effectively produced by the discharge test. Referring again to the latter models discussed above, such models used for on-line capacity measurements are often specific to particular cells and rely on measured parameters (Isamu Kurisawa and Masashi Iwata “Capacity Estimating Method of Lead-Acid Battery by Short- time Discharge”,
INTELEC
1997, 483-90). Such techniques are therefore susceptible to measurement errors. Further, the number of parameters necessary to classify an entire battery operation can become excessive making such approaches cumbersome and computationally complicated.
Alternative techniques for determining battery capacity have been proposed which are based on either open circuit voltage or charge accumulation (Minoru Kozaki, and Toshihiko Yamazaki, “Remaining Battery Capacity Meter and Method for Computing Remaining Capacity,” U.S. Pat. No. 5,691,078, Nov. 25, 1997).
In the context of telecommunications applications, the open circuit method is undesirable. Disconnecting the battery string from the power supply system would leave the telecommunication system vulnerable to switch failure and hence accidental isolation of the string from the system. Further, the charge accumulation approach requires long term monitoring of the battery (or battery string) and is dependent on knowing an accurate initial value of the battery capacity. Any initial error would affect the results of the rest of the monitoring activity. For this reason, this latter approach is considered unreliable.
It is accordingly an object of the present invention to provide a method and apparatus which allows for an accurate measurement of a batteries charge remaining (within the constraints of the application to which the battery is to be put), which avoids or at least ameliorates a number of the above mentioned problems, or at least provides the public with a useful choice.
DISCLOSURE OF THE INVENTION
In one aspect, the present invention provides for a method of testing/characterising one or more cells including the steps of:
obtaining a plurality of data points representing the direct relationship between voltage and charge remaining during an initial discharge of one or more cells; and,
parameterising the data points to obtain a function representing voltage and charge remaining, the function terminating at an end voltage corresponding substantially to a voltage level at which the cell(s) is/are considered to be exhausted, and whereby during a subsequent discharge the function allows the charge remaining to be estimated directly from the cell(s) voltage.
After the parameterisation there may be a further step of calculating the discharge reserve time. Preferably the discharge reserve time is calculated by dividing the charge remaining by either a constant power discharge rate or a constant current discharge rate.
Additionally there may be yet a further step whereby a fully charged cell or cells is subjected to a partial discharge, the charge released during the partial discharge being added to the charge remaining to obtain a measurement of capacity.
Preferably the partial discharge is one that is long enough to avoid the Coup de Fouet region, but is much shorter than a complete discharge of the cell or cells.
The steps can correspond to measuring the cell(s) voltage and current over specific time intervals.
The parameterisation can be effected by means of collecting data points equidistant in the voltage domain, a least squares fit, interpolation and/or extrapolation, or an analytical approach adapted to target the best fit to the data points.
A number of data points for a set level of measurement accuracy can be obtained and parameterised.
Preferably the data points are selected over intervals selected so as to minimise the errors inherent in the parameterisation process.
Preferably any or all of the steps may be repeated due to changes in cell characteristi
Anbuky Adnan H.
Pascoe Phillip E.
Invensys Energy Systems (NZ) Limited
Luk Lawrence
Myers Bigel & Sibley & Sajovec
Tso Edward H.
LandOfFree
Battery charge measurement and discharge reserve time... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Battery charge measurement and discharge reserve time..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Battery charge measurement and discharge reserve time... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2952674