Detection of inflection point in secondary-battery charging process by matching voltage response to first derivative of battery's characteristic curve
First Claim
1. A method of recharging a secondary battery to a substantially full-charge state and preventing overcharge by predicting an optimal charging time from the battery'"'"'s voltage response during charging, said method comprising the following steps:
- (a) developing standard reference data of a first-order time derivative of a standard voltage response of said battery during charging, wherein said reference data comprise a local maximum corresponding to an inflection point in said standard voltage response;
(b) monitoring an actual voltage response of said battery during a charging operation;
(c) computing an actual first-order time derivative of said actual voltage response during the charging operation;
(d) identifying an on-track condition during the charging operation when said computed time derivative substantially matches said standard reference data;
(e) based on the standard reference data, estimating a time period required to reach said local maximum from said on-track condition; and
(f) terminating the charging operation after said time period has elapsed after said on-track condition has been reached.
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Accused Products
Abstract
A secondary battery charging method that utilizes a standard, characteristic reference curve for that type of battery for identifying the voltage inflection point during a constant-current charging process. The voltage response of a battery being charged is sampled periodically and compared to the reference curve to establish the degree of completion of battery charge by tracking the reference curve. The charging stage of the battery is determined as the fast-charge operation progresses by identifying a place on the reference curve corresponding to the observed response. When a satisfactory match is found, the time remaining to reach a fast-charge termination point is predicted by assuming that the voltage response will track the reference curve to the inflection point. Accordingly, the voltage response is no longer monitored and the time remaining to reach the inflection point is used to complete the fast-charge operation. For the purpose of developing the reference curve, the functionality of the derivative of the standard voltage-versus-time response for the system is simulated by assuming an exponential relation during the early stages of fast-charge and a sinc function relation as the battery approaches the voltage inflection point indicating optimal termination of the fast-charge process.
27 Citations
20 Claims
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1. A method of recharging a secondary battery to a substantially full-charge state and preventing overcharge by predicting an optimal charging time from the battery'"'"'s voltage response during charging, said method comprising the following steps:
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(a) developing standard reference data of a first-order time derivative of a standard voltage response of said battery during charging, wherein said reference data comprise a local maximum corresponding to an inflection point in said standard voltage response; (b) monitoring an actual voltage response of said battery during a charging operation; (c) computing an actual first-order time derivative of said actual voltage response during the charging operation; (d) identifying an on-track condition during the charging operation when said computed time derivative substantially matches said standard reference data; (e) based on the standard reference data, estimating a time period required to reach said local maximum from said on-track condition; and (f) terminating the charging operation after said time period has elapsed after said on-track condition has been reached. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. Apparatus for recharging a secondary battery to a substantially full-charge state and preventing overcharge by predicting an optimal charging time from the battery'"'"'s voltage response during charging, comprising the following components:
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means for storing standard reference data of a first-order time derivative of a standard voltage response of said battery during charging, wherein said reference data comprise a local maximum corresponding to an inflection point in said standard voltage response; means for charging said battery; means for monitoring an actual voltage response of said battery during a charging operation; means for computing an actual first-order time derivative of said actual voltage response during the charging operation; means for identifying an on-track condition during the charging operation when said computed time derivative substantially matches said standard reference data; means for estimating a time period required to reach said local maximum from said on-track condition based on the standard reference data; and means for terminating the charging operation after said time period has elapsed after reaching said on-track condition. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification