Apparatus and method for adaptively predicting battery discharge reserve time
First Claim
1. A method of predicting the time remaining of a battery discharge until an end voltage is attained;
- comprising the steps ofcharacterizing the discharge behavior of a discharging battery with a discharge curve having a locus invariant with respect to a magnitude of the discharge current and being variant with respect to a fraction of available charge to an end voltage charge and to a function of a difference between a plateau voltage and a present voltage of the discharging battery,measuring the plateau voltage of the discharging battery,measuring a present voltage of the discharging battery to locate a point on the discharge curve,using the discharge curve for determining the fraction of available charge to an end voltage charge and expressing the fraction as a dimensionless time ratio,converting the dimensionless time ratio to a time remaining until the discharging battery reaches a selected end voltage.
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Abstract
A reliable technique of predicting the available reserve time remaining to a selected end voltage of a discharging battery is based on an adaptive state-of-charge algorithm that is active in real time to respond to changing conditions of a battery system. The adaptive state-of-charge algorithm is based on measured discharge characteristics of the battery whose reserve time is to be predicted which have been reduced to two parameters plotted as a single curve with a linear and an exponential region. These discharge characteristics are combined with dynamic parameters of the battery system which are monitored and processed in real time to provide a continuous evaluation and reevaluation of the reserve time remaining under changing conditions. As the discharge proceeds there is a continual improvement in the prediction of reserve time available.
This predictive feature embodying the principles of the invention is included in a stored program controller for a battery plant in a central office in the illustrative embodiment of the invention disclosed herein. In such applications it is highly desirable to be able to predict the available reserve time of a discharging battery until a final end voltage level is reached.
97 Citations
19 Claims
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1. A method of predicting the time remaining of a battery discharge until an end voltage is attained;
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comprising the steps of characterizing the discharge behavior of a discharging battery with a discharge curve having a locus invariant with respect to a magnitude of the discharge current and being variant with respect to a fraction of available charge to an end voltage charge and to a function of a difference between a plateau voltage and a present voltage of the discharging battery, measuring the plateau voltage of the discharging battery, measuring a present voltage of the discharging battery to locate a point on the discharge curve, using the discharge curve for determining the fraction of available charge to an end voltage charge and expressing the fraction as a dimensionless time ratio, converting the dimensionless time ratio to a time remaining until the discharging battery reaches a selected end voltage. - View Dependent Claims (2, 3, 4, 5, 6)
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7. Apparatus for predicting a reserve time for a battery discharge within a battery plant system until an end voltage is attained, comprising:
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a stored program controller including; stored data elements characterizing a discharge behavior of a battery connected to the battery plant system in terms of a battery voltage and its plateau voltage and a fraction of available charge to charge at an end voltage and further being invariant with respect to a discharge current magnitude; voltage measuring apparatus under control of the extent program controls and connected for measuring a voltage of this battery, current measuring apparatus under control of the stored program controller and connected for measuring a discharge current of the battery, the stored program controller further including instructions for initially determining a plateau voltage of the battery and ascertaining a battery voltage and discharge current at incremental time intervals, and processing measured voltage and current in order to determine through used the stored data elements a time ratio as a fraction of available charge to charge at an end voltage and converting the time ratio to a reserve time remaining for a battery discharge until an end voltage is attained. - View Dependent Claims (8, 9)
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10. A method for adaptively predicting a reserve time remaining to a discharging battery until a specified end voltage is achieved, comprising the steps of:
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selecting a standard end voltage of the discharged battery at some acceptable voltage value; characterizing a discharge for the battery into a single discharge characteristic curve functionally relating a voltage difference between a battery plateau voltage and a present terminal voltage and a dimensionless time variable and the single discharge characteristic curve having a linear region and an exponential region determined by the immediate value of the dimensionless time variable; detecting the occurrence of a discharge current from the battery; measuring a plateau voltage of the battery at an appropriate time into the discharge occurrence; measuring a terminal voltage at the battery and a discharge current of the battery initially calculating a total time of discharge for the battery to the standard end voltage utilizing the plateau voltage and dimensionless time variable and first assuming a battery discharge in the linear region of the curve; calculating a reserve time remaining from the present time to the standard end voltage; and periodically again determining a reserve time by evaluating the dimensionless time constant after a time increment by comparing the present time to the time of discharge calculated; determining if the dimensionless time constant is in the linear region; calculating a total discharge time based on the region in which the dimensionless time constant occurs; and calculating reserve time remaining to the discharging battery from the present time until the standard end voltage; continuing periodic evaluation of reserve time until the battery attains its end voltage. - View Dependent Claims (11, 12, 13)
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14. Apparatus for adaptively predicting a reserve time remaining to a discharging battery until a end voltage is achieved, comprising:
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detection apparatus for detecting an occurrence of a battery discharge; measuring apparatus for measuring a battery plateau voltage at an appropriate time after a battery discharge is initiated, and periodically measuring a battery terminal voltage and a battery discharge current; a stored program apparatus including data characterizing a discharge of the battery to a standard end voltage into a single discharge characteristic independent of the discharge current magnitude, and as a function of a difference between a battery terminal voltage and its plateau voltage and a fraction of available charge remaining in the battery; and
further including stored instructions for;initially calculating a time for a discharging battery to achieve the standard end voltage and subsequently calculating a reserve time from the present time to the end voltage, and periodically recalculating a reserve time to the end voltage until the end voltage is achieved. - View Dependent Claims (15)
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16. A method for adaptively predicting a reserve time remaining to a discharging sealed lead acid battery until a specified end voltage is attained,
comprising the steps of: -
A;
specifying an end voltage for the battery at which discharge is considered nominally completed,B;
determining a plateau voltage at which adaptive prediction of discharge begins,C;
characterizing battery discharge with a canonical discharge function relating a difference between a plateau voltage of the battery and its present terminal voltage to a present state of charge of the battery to a final charge of the battery at completion of discharge and the discharge function having an intial linear characteristic followed by a subsequent exponential characteristic,D;
monitoring a terminal voltage of the battery to determine the initial occurrence of a discharge,E;
marking an occurrence of a plateau voltage during discharge of the battery and continuously measuring elapsed time of discharge after its occurrence,F;
initially estimating discharge time remaining until a specified end voltage is attained by calculating a quantity of battery charge available to attainment of the discharge voltage with the equation, ##EQU7## G;
calculating the reserve time remaining with the equation,
space="preserve" listing-type="equation">t.sub.r =(q.sub.ev -q.sub.t)/I(t)H;
terminating calculation of reserve time if the battery voltage has attained the specified end voltage value,I;
calculating a dimensionless time ratio with the equation, ##EQU8## J;
evaluating the dimensionless time ratio to determine the present operating locus within one of the linear and exponential characteristics,K;
again estimating discharge time remaining until a default end voltage is attained by calculating a quantity of battery charge remaining with a calculation appropriate to the present operating locus,L;
performing calculations in the linear characteristic with the equation, ##EQU9## M;
calculating the reserve time remaining until the specified end voltage is attained with the equation,
space="preserve" listing-type="equation">t.sub.r =(q.sub.ev -q.sub.t)/I(t)N;
performing calculations in the exponential characteristic with the equation, ##EQU10## O;
calculating the reserve time remaining until the specified end voltage is attained with the equation,
space="preserve" listing-type="equation">t.sub.r =(q.sub.ev -q.sub.t)/I(t)P;
continuously monitoring a voltage of the battery and iteratively repeating steps [I] through [O] until the specified end voltage is reached. - View Dependent Claims (17, 18, 19)
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Specification