FR2925783A1 - Storage cell group charging/discharging system for e.g. electric traction motor vehicle, has charging/discharging applying current when condition is attained and stopping conditions are not attained such that intensity of current is limited - Google Patents

Abstract

The system has a balancing device (11-1) constituted by a zener diode and by-passing total or part of charging or discharging current of a storage cell of a group of storage cells (10-1) when preset loading or unloading stopping conditions are attained. A charging or discharging device (12) constituted by a direct current-direct current converter applies the current to the cell when a specific condition is attained and the stopping conditions are not attained such that intensity of the current by-passed by the device (11-1) is limited for the cell when the stopping conditions are attained.

Description

System for charging / discharging a group of at least one storage cell.

The present invention relates to a charging / discharging system of a group of at least one storage cell for a vehicle, in particular a motor vehicle, electric traction or mixed thermal / electrical traction. Such charging / discharging systems are already known which generally comprise an electrical energy storage device which generally consists of a plurality of elementary storage units, also known in the field of the "storage cell" technique, identical and interconnected in series so as to obtain at the terminals of said storage device a sufficiently high voltage to power the electrical organs of said vehicle.

However, due to disparities in the manufacturing process of these storage cells, the characteristics of the cells can vary substantially from one cell to another. This results in problems due to load differences and therefore voltage between cells of the same storage device. For example, while a cell has reached its maximum load and is delivering its maximum voltage, an other cell of the same storage device can be loaded above its maximum allowable load and thus deliver a voltage greater than that which is delivered by the first cell. This can be particularly damaging in the case of using storage cells of certain technologies, for example storage cells consisting of supercapacitors, whose terminal voltage must remain in a determined range of voltages under penalty of deterioration. To solve this problem, and thus allow the voltage at the terminals of each storage cell of the same storage device not to exceed a maximum voltage, it is common to use balancing circuits, each connected to the terminals. a storage cell with which it is associated. These balancing circuits are designed to derive the current flowing through the associated storage cell when the voltage at the terminals of this cell exceeds a predetermined threshold. Nevertheless, because the intensity of the charging or discharging current of the storage cells is high, which may be of the order of 100 amperes, these balancing circuits use components which can pass such currents and which are therefore expensive and bulky (in electrical terms: wiring, etc. than thermal radiator, etc.), which is detrimental to the industrial exploitation of certain cell technologies. There are also balancing circuits designed to derive currents of lower intensity, but in this case, the triggering threshold of the balancing must provide a margin with respect to the voltage limit of the cells, this margin being necessary to compensate for fluctuations during the balancing phase.

The object of the invention is to remedy the disadvantages mentioned above by proposing a charging / discharging system of a group of at least one storage cell, said system comprising a charging / discharging device connected to the terminals of said group of cells. at least one storage cell and a balancing device connected to the terminals of each storage cell of said group of at least one storage cell, said or each balancing device being designed to derive all or part of the charging current discharging the associated storage cell when predetermined conditions for stopping charging or discharging said cell are reached.

For this purpose, said system is characterized in that said charging / discharging device is provided for applying to the associated storage cell or cells a charge or discharge current of limited intensity when particular conditions are fulfilled and whereas the charge or discharge stop conditions are not reached for any storage cell, so that the intensity of the derived current by a balancing device while the conditions for stopping charging or discharging are reached for the associated cell, either limited. According to one embodiment, said charging / discharging device is provided for applying to the associated storage cell or cells a charging or discharging current of limited intensity when the voltage at its terminals is greater than and / or less than less a threshold voltage. According to another embodiment, said charging / discharging device is designed to apply to the associated storage cell or cells a charge or discharge current of limited intensity when the vehicle's life phase is favorable there. According to one embodiment, said or each balancing device consists of an electronic switch whose active terminals are respectively connected to the terminals of the associated storage cell and the control terminal is connected to the common point of two resistors, they themselves connected to the terminals of the associated storage cell or cells.

According to another embodiment, said or each balancing device consists of two diodes, one of which is a Zener diode, their anodes being interconnected equipotentially and their cathodes being respectively connected to the terminals of the associated storage cells. Advantageously, said charging / discharging device consists of a traction inverter controlled so as to control the charge and discharge current so as to limit the charging / discharging current which it delivers when the voltage at its terminals is greater than at a first threshold value and / or is less than a second threshold value. Advantageously, said charging / discharging device consists of a DC / DC converter, also called DC / DC, the inputs of which are connected to a power source that the one or more storage cells and whose outputs are connected to the group. storage cells, said DC / DC converter being provided to limit the charging / discharging current that it delivers during prolonged phases of non-use of said group of at least one storage cell. The invention will be better understood, and other objects, features, details and advantages thereof will appear more clearly in the following explanatory description made with reference to the accompanying schematic drawings, given solely by way of example, illustrating embodiments of the invention and in which: - Figure 1 is a block diagram of a charging / discharging system according to the present invention; - Figure 2 is a block diagram of a first particular embodiment of a device for balancing a charging / discharging system according to the present invention, and - Figure 3 is a block diagram of a second particular embodiment of a device for balancing a charging system. / discharge according to the present invention. A charge / discharge system is intended to ensure the charging and / or the discharge of at least one storage cell 10. The embodiment of a charge / discharge device according to the invention, as it is shown in FIG. 1, is composed, on the one hand, of at least one load balancing device 11 and, on the other hand, of a charging / discharging device 12. In FIG. charge / discharge is intended for a group of three cells 101 to 103 and comprises three balancing devices 111 to 113 respectively connected in parallel across the cells 101 to 103. Each balancing device 11 is designed to derive the current from charge of the cell 10 to which it is connected when the voltage across its terminals (and therefore at the terminals of the corresponding storage cell 10) is greater and / or lower, depending on the type of balancing device, than at least one threshold voltage . As for the charging / discharging device 12, it is provided with means (not shown) for, when the voltage at its terminals is higher and / or lower, depending on the type of charging / discharging device, at at least one threshold voltage, limiting the charge / discharge current that it delivers to a value lower than its charge / discharge value when this threshold voltage is not reached. The operation of the charging / discharging system is as follows, applied to the case of the load and to a plurality of storage cells, for example ten in number, whose maximum voltage per cell in operation is 2.5 volts. As long as the voltage across the charging / discharging device 12 is less than 10 × 2.5 volts = 25 volts, the charging current is maximum, for example 100 A. On the other hand, as soon as the voltage at the terminals of the device charge / discharge 12 becomes greater than 25 volts, the intensity of the current delivered by the charging / discharging device 12 drops to a lower value, for example 1 A. This voltage of 25 volts can be reached, for example, because five storage cells 10 have a charging voltage of 2.4 volts and the other storage cells have a charging voltage of 2.6 volts.

Suppose that the threshold value of each balancing device is 2.7 volts. Later, when the voltage across the storage cells 10 which was at 2.6 volts becomes equal to 2.7 volts, the charge current of these cells, which has a relatively low value compared to the normal charge value of the cell is diverted to the corresponding balancing device. It should be noted that the power dissipated by this balancing device is 2.7 volts x 1 A, or 2.7 watts. As for the other storage cells, they continue to charge with a current of 1 A which passes through them. Still later, all the storage cells have voltages at their terminals of 2.7 volts. The current then delivered by the charging / discharging device no longer passes through any of these cells. The numerical examples given here are for illustrative purposes only to explain the operation of the charging / discharging system according to the invention. It will also be understood that said charging / discharging system 12 may also operate for discharge of the storage cells. Thus, when the voltage across the charging / discharging device 12 becomes lower than a threshold value, the intensity of the discharge current drops to a lower value. Likewise, when the voltage at the terminals of each balancing device 11 becomes lower than a threshold value, the discharge current is derived in said balancing device 11. According to another embodiment of the invention, the device for charge / discharge 12 comprises means for limiting the intensity of the charge / discharge current that it delivers when the voltage at its terminals is greater than a first threshold value and is less than a second threshold value.

It will be noted that the traction inverter already present on the vehicle, but controlled to control the charging and discharging current in the manner explained above, could be used as charging / discharging device 12. that is to say, so as to limit the charge / discharge current that it delivers when the voltage across its terminals is greater than a first threshold value and / or is lower than a second threshold value. One could also use an inverter associated with a generator or even a generator which one would control the current it delivers. Similarly, it could be a DC / DC converter whose inputs are connected to another power source such as electric batteries already present in the vehicle or to a mains charger in the case of a rechargeable vehicle and whose outputs are connected to the group of storage cells 10. Such a DC / DC converter could be provided for balancing a group of storage cells 10 during long periods of non-use of the vehicle by exchange of data. energy between the other power source and the cells. It is shown in FIG. 2 an exemplary embodiment of a balancing device 11 which is provided for deriving the load current which passes through the storage cell 10 at the terminals of which it is connected when the voltage at its terminals becomes lower than a threshold value. It consists of an electronic switch 110 (here consisting of a FET transistor or equivalent) whose active terminals 110a and 110b are respectively connected to the terminals of the associated storage cell 10 and the control terminal 110c is connected to the common point two resistors 111a and 111b themselves connected to the terminals of the associated storage cell 10.

When the voltage at the terminals of the storage cell 10 is high, the potential difference between the active terminal 110b and the control terminal 110c is greater than the threshold voltage, so that the switch 110 is open (the transistor n ' is not passing). On the other hand, when the voltage at the terminals of the storage cell 10 is lower than a voltage such that the potential difference between the active terminal 110b and the control terminal 110c becomes lower than the threshold voltage, the switch 110 closes. (The transistor is on) and the charging current of the cell 10 now passes through the switch 110. In FIG. 3 another embodiment of a balancing device 11 which is provided for deriving the load current which passes through the storage cell 10 to which it is connected when the voltage at its terminals becomes greater than a threshold value . It consists of two diodes 112 and 113, one of which is a Zener diode, the anodes of said two diodes being interconnected equipotentially and the cathodes being respectively at the terminals of the associated storage cell 10. When the voltage across the storage cell 10 is low, none of the diodes 112 and 113 is conductive. On the other hand, when the voltage at the terminals of the storage cell 10 is greater than the Zener voltage of the diode 112 increased by the direct voltage of the diode 113 (approximately 0.7 volts), the two diodes 112 and 113 conduct, allowing the charge current of the cell 10 to now pass through the diodes 112 and 113. The advantage of the present invention results from the fact that the charging / discharging device 12 makes it possible to limit the charging or discharging current when conditions all storage cells 10 are filled or when the life phase of the vehicle is propitious and while the conditions for stopping charging or discharging are not reached for any storage cell 10. When these latter conditions are achieved for at least one of the storage cells 10, the associated balancing device 11 can derive the charge or discharge current whose relatively low intensity of the moment allows the use of balancing devices 11 simpler, cheaper, less bulky from an electrical point of view (smaller components, smaller wiring, etc.) but also from a thermal point of view (no radiator of cooling, in particular) than the balancing devices used in the charging / discharging systems of the prior art.

Claims (7)

A system for charging / discharging a group of at least one storage cell, said system comprising a charging / discharging device connected across said group of at least one storage cell and a balancing device connected to terminals of at least one storage cell of said group of at least one storage cell, said or each balancing device being arranged to derive all or part of the charging / discharging current of the associated storage cell or cells when predetermined conditions for stopping charging or discharging said cell are achieved, characterized in that said charging / discharging device is provided for applying to the associated storage cell or cells a charge or discharge current of limited intensity when special conditions are fulfilled and the conditions for stopping charging or discharging are not reached for any storage cell, so that e the intensity of the derived current by a balancing device while the conditions of stopping charge or discharge are reached for the associated cell or cells is limited. 2. charging / discharging system according to claim 1, characterized in that said charging / discharging device is provided for applying to the associated storage cell or cells a charge or discharge current of limited intensity when the voltage at its terminals is greater and / or less than at least one threshold voltage. 3. Charge / discharge system according to claim 1 or 2, characterized in that said charging / discharging device is provided for applying to the associated storage cell or cells a charge or discharge current of limited intensity when the phase life of the vehicle is propitious. 4. Charge / discharge system according to one of the preceding claims, characterized in that said or each balancing device consists of an electronic switch 110 whose active terminals 110a and 110b are respectively connected to the terminals of the cell. associated storage and the control terminal 110c is connected to the common point of two resistors 111a and 111b themselves connected to the terminals of the or associated storage cells 10. 5. Charge / discharge system according to one of the preceding claims, characterized in that said or each balancing device consists of two diodes (112 and 113), one of which is a Zener diode, their anodes being connected between they are equipotentially and their cathodes are respectively connected to the terminals of the or associated storage cells 10. 6. Charge / discharge system according to one of the preceding claims, characterized in that said charging / discharging device 12 consists of a traction inverter controlled to control the charging and discharging current so as to limit the charging / discharging current that it delivers when the voltage at its terminals is greater than a first threshold value and / or is less than a second threshold value. 7. Charge / discharge system according to one of the preceding claims, characterized in that said charging / discharging device 12 consists of a DC / DC converter whose inputs are connected to another storage member that said one or more storage cells and whose outputs are connected to the group of storage cells 10, said DC / DC converter being provided to limit the charge / discharge current that it delivers during extended periods of non-use.