Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1996-06-14
1997-10-14
Tso, Edward
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 15, H01M 1044, H01M 1046
Patent
active
056776136
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method of regulating the charging of a set of electrical storage cells, and to a facility for implementing the method.
BACKGROUND OF THE INVENTION
In known manner, such a set is conventionally made up of a plurality of units, each of which is identically made up of one or more identical electrochemical cells, the units being connected together in series via their respective power supply terminals.
Charging such a set by means of a charger connected to the end terminals of the set generally does not take place uniformly for all of the units. The electrical and chemical characteristics of the units in the same set vary over time and as a function of the operating conditions of the set. This results in particular in the various units of the same set not reaching their respective fully charged levels simultaneously during recharging.
It is therefore known that a current can be maintained at the end of charging of a set comprising a plurality of units in order to ensure that all of the units are fully charged including those which are the slowest to become recharged. Unfortunately such a solution to the problem is not without its drawbacks, because the units that reach their fully charged levels first continue unnecessarily to pass the charging current which heats them up and can lead to gases being given off, or, when the units are made up of sealed cells, to excessive pressure building up.
A known solution for remedying this consists in regulating the charging current for each unit as a function of the voltage across its terminals by means of a circuit making it possible to divert a progressively increasing fraction of the current away from the unit, at the end of unit charging, once a voltage threshold representative of the end of charging is reached. However, such a solution is not entirely satisfactory for a set having a large capacity for supplying high currents, e.g. such as the sets intended for use in electrically powered vehicles. The currents required for recharging such sets can also be high, which means that the currents to be diverted are also high, and that the power dissipated for regulation purposes at the end of charging is high.
SUMMARY OF THE INVENTION
The invention therefore provides a method of regulating the current supplied by a charger to the end terminals of a set of electrical storage cells, which set is made up of a plurality of units, each of which is identically made up of one or more identical electrochemical cells, the units being connected together in series via their respective power supply terminals, each unit being provided with an individual interface including measurement means for measuring the voltage across its power supply terminals, means for diverting a portion of the charging current supplied to the unit, when the measured voltage is greater than a threshold value, and means for supplying measurement signals to a controller of the charger.
According to a characteristic of the invention, provision is made for the controller to reduce progressively the charging current supplied by the charger to the set, when a current measurement signal is received from at least one of the interfaces, which current measurement signal expresses the existence of a current diverted at the interface, so long as the charging current supplied to the set is greater than the sum of the currents that can be diverted by the interfaces, the charging current then being maintained at the same level until current measurement signals are received that express the fact that the diversion means for all of interfaces of the units of the set are operating.
The invention also provides a facility associating, at least temporarily, a charger with a set of electrical storage cells, the charger being connected to the end terminals of the set, the set being made up of a plurality of identical units, each of which comprises one or more electrochemical cells, the units being connected together in series via their respective power supply terminals. Each un
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D. Hopkins et al, "Dynamic Equalization During Charging of Serial Energy Storage Elements", IEEE Transaction on Industry Applications, vol. 29, No. 2, Mar. 1993, New York, US pp. 363-367.
B. Lindemark, "Individual Cell Voltage Equalizers (Ice) for Reliable Battery Performance", 13th International Telecommunications Energy Conference, 5 Nov. 1991, Japan, pp. 196-201.
SAFT
Tso Edward
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