Method of optimizing the charging of a battery of storage cells, and apparatus for performing the method

Claim 3

A method according to claim 1, characterized in that it further comprises periodically: re-determining the charge balance and a new temperature of the battery; obtaining a value for a new charging capacity that corresponds to the new temperature; comparing the charge balance with the new charging capacity; an deciding again either to switch from maintenance mode to charging mode, or to switch from charging mode to maintenance mode as a function of the result of the previous comparison.

Claim 4

A method according to claim 1, characterized in that, in order to determine the reference capacity of the battery at a reference temperature, the method comprises: charging the battery until overcharging occurs, which overcharging is detected by comparing a threshold value with the difference between the temperature (Tb) of the battery and the ambient temperature (Ta); taking the value of the reference capacity to be the charge balance; and taking the reference temperature to be the temperature of the battery at the end of charging.

Claim 5

A method according to claim 2, characterized in that said switching step comprises switching from maintenance mode to charging mode only if: the difference between the temperature (Tb) of the battery and ambient temperature (Ta) is less than a threshold value defining a permitted positive temperature difference for the battery at the start of charging; and the temperature of the battery is less than a threshold value limiting the temperature that the battery is permitted at the start of charging; and the charge balance is less than the charging capacity.

Claim 6

A method according to claim 4, characterized in that it further comprises: determining and storing the temperature (Tbfc) of the battery at the end of each charging period; and taking as the threshold value defining the limit temperature that the battery is permitted at the start of charging: the temperature (Tbfc) stored at the end of the charging period preceding the period in question, if the period in question is not the first charging period after a period of discharging to an external circuit; and a predetermined value, if the period in question is the first charging period after a period of discharging to an external circuit.

Claim 7

A method according to claim 2, characterized in that said switching step comprises switching from charging mode to maintenance mode: if the temperature difference (Ta-Tb) of the battery above ambient temperature is greater than a threshold value defining the maximum positive temperature difference that the battery is permitted at the end of charging; or if the charge balance is greater than the charging capacity.

Claim 8

Apparatus for optimizing the charging of a battery of storage cells by charging said battery at a first rate in charging mode for compensating for discharging of said battery to an external circuit, and charging said battery at a lower second rate in a maintenance mode for compensating for self-discharging of the battery, said battery being characterized by a charge balance corresponding to a difference between an amount of charge supplied to said battery and an amount of discharge from said battery to said external circuit, said charging being optimized by calculating a threshold value corresponding to a charge that the battery can store without manifesting overcharging phenomena, the calculated value being referred to as the "charging capacity" of the battery and being calculated as a function of (1) a "reference" capacity which is the charging capacity of said battery at a reference temperature, (2) a difference between a temperature (Tb) of the battery at the moment in question and the reference temperature, and (3) a predetermined relationship for variation in charging capacity as a function of temperature (Tb) for the battery, comparing said charge balance with said threshold value, and switching between said maintenance mode and said charging mode as a function of the result of said comparison, said apparatus comprising: first means responsive to a charge signal and a maintain signal, respectively, for supplying the battery either with a charging current for said charging mode or with a maintenance current for said maintenance mode; second means for determining said charge balance and for multiplying said charge balance by a predetermined weighting coefficient; and third means for generating a threshold value comprising an estimate of the charge that the battery can store without manifesting any overcharging phenomena, the value being referred to as the "charging capacity" of the battery, and being estimated as a function of: a "reference" capacity which is the charging capacity at a reference temperature; the difference between the temperature (Tb) of the battery at the moment in question and the reference temperature; and a predetermined relationship for the variation in charging capacity as a function of temperature (Tb) for the battery; fourth means for comparing the charge balance with said threshold value and for supplying either a charge signal or a maintain signal as a function of the result of the comparison.

Claim 9

Apparatus for optimizing the charging of a battery of storage cells by charging said battery at a first rate in charging mode for compensating for discharging of said battery to an external circuit, and charging said battery at a lower second rate in a maintenance mode for compensating for self-discharging of the battery, said battery being characterized by a charge balance corresponding to a difference between an amount of charge supplied to said battery and an amount of discharge from said battery to said external circuit, said charging being optimized by calculating a threshold value corresponding to a charge that the battery can store without manifesting overcharging phenomena, the calculated value being referred to as the "charging capacity" of the battery and being calculated as a function of (1) a "reference" capacity which is the charging capacity of said battery at a reference temperature, (2) a difference between a temperature (Tb) of the battery at the moment in question and the reference temperature, and (3) a predetermined relationship for variation in charging capacity as a function of temperature (Tb) for the battery, comparing said charge balance with said threshold value, and switching between said maintenance mode and said charging mode as a function of the result of said comparison, said apparatus comprising: first means responsive to a charge signal and a maintain signal, respectively, for supplying the battery either with a charging current for said charging mode or with a maintenance current for said maintenance mode; second means for determining said charge balance and for multiplying said charge balance by a predetermined weighting coefficient; and third means for generating a threshold value comprising an estimate of the charge that the battery can store without manifesting any overcharging phenomena, the value being referred to as the "charging capacity" of the battery, and being estimated as a function of: a "reference" capacity which is the charging capacity at a reference temperature; the difference between the temperature (Tb) of the battery at the moment in question and the reference temperature; and a predetermined relationship for the variation in charging capacity as a function of temperature (Tb) for the battery; fourth means for comparing the charge balance with said threshold value and for supplying either a charge signal or a maintain signal as a function of the result of the comparison.

Claim 10

Apparatus according to claim 7, characterized in that the third means comprises: fifth means for periodically re-determining the charge balance and a new temperature (Tb) of the battery; and sixth means for obtaining a new value of capacity that corresponds to each new temperature; and in that the second and fourth means the electricity balance and for supplying either a charge signal include seventh means for: re-establishing the charge balance periodically, comparing each new charge balance with a new value of capacity, and supplying a new charge signal or a new maintain signal as a function of the result of the comparison.

Claim 11

Apparatus according to claim 7, characterized in that the fourth means comprises: fifth means for determining the ambient temperature (Ta); sixth means for determining the temperature of the battery; seventh means for determining the temperature difference (Tb-Ta) of the battery above ambient temperature, and for comparing the difference with the temperature (Tb) of the battery at a threshold value defining the maximum temperature that the battery is permitted at the start of charging; and eighth means for supplying a charge signal if: the electricity balance is less than the charging capacity; and the temperature difference (Tb-Ta) of the battery is less than the maximum permitted positive difference; and the temperature of the battery (Tb) is less than the maximum permitted temperature.

Claim 12

Apparatus according to claim 9, characterized in that the fourth means further comprises: ninth means for determining and storing the temperature (Tbfc) of the battery at the end of each charging period; and tenth means for determining a threshold value defining the limit temperature that the battery is permitted at the start of charging, the threshold value being equal to: the temperature (Tbfc) determined at the end of the charging period preceding the charging period in progress, if the charging period in progress is not the first charging period after a period of discharging to an external circuit; or a predetermined value, if the charging period in progress is the first charging period after a period of discharging to an external circuit.

Claim 13

Apparatus according to claim 7, characterized in that the fourth means comprises: fifth means for determining the temperature (Tb) of the battery; sixth means for determining the ambient temperature (Ta); seventh means for determining the temperature difference (Tb-Ta) of the battery above ambient temperature, and for comparing the difference with a threshold value defining the maximum positive temperature difference that the battery is permitted at the end of charging; and eighth means for supplying a maintain signal if: the electricity balance is greater than the charging capacity; or the temperature of the battery is greater than the maximum permitted temperature.