FR2981520A1 - Method for managing electric energy storage battery i.e. lithium-ion battery in electric car, involves disconnecting series connection of selected storage elements, and performing parallel connection between disconnected storage elements - Google Patents

Abstract

The method involves selecting, from among several storage elements (E1, Ej, EN) connected in series, two storage elements across which electric voltages are different. The series connection of the selected storage elements is disconnected, and a parallel electric connection is performed between the disconnected storage elements, where the number of selected storage elements is smaller than the number of storage elements included in a lithium-ion battery, and a portion of non-selected storage elements remains interconnected electrically in series. An independent claim is also included for a device for managing an electric energy storage battery.

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to the field of management of an electric energy storage battery which comprises a plurality of individual energy storage elements intended to be used. to be connected in series.

The subject of the invention is more particularly a management method including a step for balancing the electrical charges of these storage elements, as well as a management device that implements the management method and a motor vehicle comprising such a device. State of the art The batteries used in electric vehicles, for example of the Lithium-Ion type, consist of a set of storage elements, for example electrochemical cells, which are connected in series and possibly also in parallel to reach the voltage and capacity levels requested by the application.

The existing manufacturing processes today do not allow to have perfectly identical cells, especially on characteristics such as their capacity and their internal resistance. In addition, these elements undergo, during the life of the battery pack, different temperature variations due to their location in the pack, which causes them to age heterogeneously. When these elements with different characteristics, assembled in series in the battery, are crossed by the same current, they are out of balance. Battery management devices correct this imbalance, to allow optimal use of the energy contained in the battery pack (the range of use of the pack being determined by the most loaded cell and the least loaded cell). The balancing can be done from information of the state of charge of the elements (SOC) or their voltage or their voltage when empty.

The balancing methods currently used are active or passive: - the passive balancing (or dissipative) discharges the most charged cells in dissipative elements (resistances, for example) so that they all have the same state of charge; active (or non-dissipative) balancing transfers the energy from the most charged cells to the most unloaded cells, in order to converge towards the same state of charge.

Balancing solutions are described in US5631534, US20110068744 and WO2004049540 for example, but they are complex and expensive with the use of a large number of electronic components.

Another balancing solution is known from EP1869748B1 which describes the principle of paralleling the plurality of cells contained in each of the modules of the battery, then paralleling all the modules. This balancing is practiced in the situation of discharging the battery to make voltage balancing cells between them, and modules between them. However, this solution is not very flexible because all the modules and cells are balanced, and does not allow operation of the battery during the balancing operation. Object of the invention The object of the present invention is to propose a method of managing the battery. a battery that overcomes the disadvantages listed above. A first object is in particular to be able to balance a battery in a non-dissipative manner, that is to say, by charge transfer. A second object is to provide a simpler solution at a lower cost than current solutions in the "non-sensing balancing" class.

A third object is to provide a flexible solution allowing the transfer of energy between any elements of the battery, whether the battery is in use or not. A first aspect of the invention relates to a method of managing a battery of electrical energy storage comprising a plurality of storage elements intended to be electrically connected to each other in a series connection, the management method comprising a step of balancing the electrical charges comprising itself: a selection step, among the plurality of storage elements, at least two storage elements across which the electrical voltages are different, - a step of disconnection out of the series connection, the storage elements selected in the selection step, - and a step of electrically connecting them in parallel assembly of all or part of the disconnected storage elements in step d e disconnection.

The number of storage elements selected at the selection step may be less than the total number of storage elements in the farm, at least a portion of the storage elements not selected at the selection stage remaining connected to each other electrically in series at the end of the connection step.

The storage elements selected at the selection step may be located at any location within the serial array, adjacent or not.

In the case where at least two of the storage elements selected in the selecting step are located at non-adjacent locations within the serial array, the unselected storage elements implanted in the serial connection between said locations can be connected. during the connection step, in the parallel connection with the selected storage elements. The connection step may include closing "bypass" branch branches each configured to bypass at least one of the storage elements selected at the selection step within the serial arrangement. In case of use of the battery, the management method may include a step of charging and / or electrically discharging the storage elements of the battery connected in series after the connection step. be performed in the event of the battery not being used without charge and / or electric discharge of any storage element of the battery from outside the battery.

The balancing step may be such that the number of storage elements selected in the selection step is equal to the total number of storage elements of the battery, and that all the storage elements of the battery are connected in parallel with each other following the connection step.

The selection of the storage elements in the selection step may be a function of selection criteria taking into account the allowable drop in the no-load voltage of the battery and / or a desired dynamic of the balancing and / or threshold value of the electrical current in the parallel connection. A second aspect of the invention relates to a device for managing an electric energy storage battery comprising, on the one hand, a plurality of storage elements and, on the other hand, a connection structure intended to electrically connect the storage elements. storage between them in a series connection, further comprising software and / or hardware means that implement such a management method. The connection structure may comprise electrical connections between the storage elements and switching elements arranged on the electrical connections, the electrical connections and the switching elements being able to be controlled so that the connection structure can vary between at least a first one. state in which all or part of the storage elements are electrically connected to each other in a series connection and at least a second state in which all or part of the storage elements are electrically connected to each other in a parallel connection. It may include a control unit generating actuation commands driving the switching elements so as to vary the connection structure from one state to another in a manner performing the balancing step. The switching elements may be "MOSFET" insulated gate field effect transistors. Each storage element of the battery may consist of a supercapacity or an electrochemical unit cell or a member having at least two such electrically connected cells in parallel or a module comprising at least two such electrically connected members in series with each other or an assembly comprising at least two such modules electrically connected in series with each other. A third aspect of the invention relates to a motor vehicle comprising such a management device for controlling the electric energy storage battery supplying an electric traction system of the vehicle and / or electrical auxiliary devices on board the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given by way of nonlimiting example and represented in the accompanying drawings, in which: FIG. 1 schematically represents a part of a first embodiment of management device, - Figures 2 to 4 illustrate the elements of Figure 1, respectively in a first, a second and a third balancing modes, - Figure 5 represents schematically a part of a second embodiment of management device, - Figures 6 and 7 explain the principle of balancing applied to two electrochemical cells, - Figures 8 and 9 explain the principle of balancing applied to N pairs of cells connected in series, by their paralleling, - and Figures 10 and 11 explain the principle of balancing applied N modules in series (each comprising two such pairs in series) by their parallel connection. DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION A management device is partially illustrated in FIGS. 1 to 5 and configured for the control of an electrical energy storage battery of terminals A and B comprising on the one hand a plurality of storage elements El, ..., EJ, ..., EN and on the other hand a connection structure for normally connecting all or part of these storage elements to each other in at least one electrically connected series.

Moreover, the management device comprises software and / or hardware means which implement a management method which will be detailed later. In particular, each storage element of the battery is constituted in the rest of the description by either a supercapacity, or an electrochemical unit cell (FIGS. 6 and 7), or an organ with at least one pair of such cells (FIGS. 8 and 9). ) electrically connected in parallel (each pair being commonly called "bicell"), ie a module comprising at least two such members electrically connected in series with each other, or else an assembly comprising at least two such modules electrically connected in series or in parallel between them. The connection structure comprises on the one hand electrical connections between the storage elements and on the other hand switching elements (detailed below) arranged along the electrical connections to respectively control the opening or closing of the link. The electrical connections are configured and the switching elements can be controlled so that the connection structure can vary between at least a first state in which all or part of the storage elements are electrically connected to each other in a series connection and at least a second state in which all or part of the storage elements are electrically connected to each other in a parallel connection. In general, in each of the states, the number of elements in series in the series connection can be variable and adjustable and the number of elements assembled in parallel in the parallel connection can also be variable and adjustable. In the case of a second state, the connection structure possibly allows all or part of the possible storage elements not belonging to the parallel connection to be simultaneously connected in series with each other. In a simple embodiment, the connection structure comprises in particular a main branch formed by direct electrical connections each connecting two to two storage elements to form the series assembly. It also comprises a first and a second deflection branches each arranged along the series circuit, and to which each of the direct electrical connections is connected once by means of an associated connection electrical connection. Referring to Figure 5, it is also possible to provide a branch branch configured each to shunt at least one of the storage elements of the serial assembly. For the implementation of the management method, the management device comprises a control unit generating actuation commands driving the switching elements so as to vary the connection structure from one state to another in a manner performing a step of balancing the electrical charges of all or part of the storage elements, the elements implemented by the balancing operation being selectable from all the elements that comprises the battery.

Advantageously, the switching elements are insulated gate field effect transistors more commonly known as "MOSFET" in the English terminology for "Metal Oxide Semiconductor Field Effect Transistor". This variant has the advantage of being controlled in voltage to control the current in the circuit. However, the switching elements can be of any other nature, such as relays or others. According to an essential characteristic, the management device therefore implements a management method of the electric energy storage battery including in particular a balancing step of the electric charges, this last step comprising the following steps that are not necessarily successive: a step of selecting, among the plurality of storage elements, at least two storage elements at the terminals of which the electrical voltages are different, - a step of disconnection out of the series connection, at least storage elements selected to the selection step, and an electrical connection step between them in a parallel assembly of all or part of the storage elements disconnected at the disconnection step. It should be noted that the number of elements removed at the disconnection step may be greater than the number of elements selected at the selection step (see Figures 2 and 3 which illustrate that two elements may be selected while three elements can be disconnected because in these figures the middle element is disconnected at the disconnection step although it was not necessarily selected). In addition, all disconnected elements out of the serial circuit at the disconnection step are not necessarily connected in parallel to the connection step. FIG. 3 explains this situation where it is possible to provide for only two storage elements to be paralleled at the connection step even in the case where three of the serial assembly are disconnected at the disconnection step.

The advantage of this method is to use a charge transfer based on a physical property of electrical systems, namely the fact that elements connected in parallel have the same voltage. Thus, the connection structure makes it possible to separate the serial storage elements of the battery and to put them in parallel, their empty voltage is naturally balanced and therefore the differences in state of charge are compensated. According to a particular but not mandatory embodiment, the number of storage elements selected in the selection step is less than the total number of storage elements included in the battery so that at least a portion of the storage elements not selected in the selection step remain electrically connected to each other in series at the end of the connection step. This possibility is shown for example in Figures 2 and 3 where only two storage elements are selected while the battery contains at least three. On the other hand, the storage elements selected in the selection step may advantageously be located at any location within the series arrangement, whether adjacent (Figure 2) or not (Figure 3). In the particular case where at least two of the storage elements selected in the selection step are located at non-adjacent locations within the series connection, the storage elements not selected and yet located in the series connection between said locations can be connected, during the connection step, in the parallel connection with the selected storage elements. This is illustrated in Figure 4 where the central element is connected in parallel with the two side elements although the central element has not been selected. The main advantage of the connection structure implemented in FIG. 5 is to allow the connection step to include the closing of bypass branches, each configured to bypass at least one of the storage elements selected at the gate. selection step within the serial assembly. In this case, the storage elements not selected and yet implanted in the series connection between the non-adjacent locations of selected elements can be connected, during the connection step, in the series connection with all the non-storage elements. selected.

On the one hand the possibility that the connection step is such that elements remain in series and secondly the possibility that branch branches are closed to shunt the elements connected in parallel, in case of use of the battery, the management method potentially comprises a step of charging and / or electrically discharging the storage elements of the battery connected in series after the connection step.

Advantageously, the balancing step can also be performed in case of non-use of the battery without charge and / or electric discharge of any storage element of the battery from outside the battery, that is to say without any energy exchange with an external system such as a charger or motor, the balancing process resulting in energy exchanges within the battery. In this variant, the balancing step will then be advantageously such that the number of storage elements selected in the selection step is equal to the total number of storage elements of the battery, and that the set of elements storage of the battery are connected in parallel with each other as a result of the connection step. The selection of the storage elements in the selection step is a function of selection criteria taking into account, for example: the admissible drop in the battery's no-load voltage, and / or a desired dynamic of the balancing, and / or a threshold value of the electrical intensity in the parallel connection. In the second case, it is possible in particular to associate in parallel the elements having the lowest voltage with the elements having the highest voltage.

In the third case, the choice of elements must take into account a maximum value of the voltage difference to be balanced within the assembly.

A particular but non-exclusive application consists in arranging such a management device on board a motor vehicle to control the battery for storing electrical energy supplying an electric traction chain of the vehicle and / or auxiliary electrical components on board the vehicle. vehicle. However, the invention can be applied to any battery system which is composed of at least two electrochemical cells in series, such as laptop batteries, for example, or even the balancing of supercapacities. The invention, which allows switching between the serial association and one or more associations in parallel of the elements to be balanced, will be better understood from the examples below. The switching is done according to the diagram of operation shown for example in Figure 1. The switching elements positioned on the direct electrical connections between each element in series make it possible to undo the series assembly of the battery pack when it is not in use for example (that is, when at rest). Then the switching elements Cp1, Cp, 2, Cp, 2j_1, Cp, 2j, Cp, 2N_IetCp2N which equip the electrical connection connections to the two branches of deflection are closed, for the paralleling of the selected elements. Of course, the paralleling of elements with different voltages generating a current draw, it is interesting to use "mosfets" controlled voltage to control the current in the circuit. In addition, it should be noted that an element has a capacitive effect that tends to limit current draws. The idle battery can remain on this configuration in parallel, which will allow, with the following use, to find all the elements in equilibrium. Before this use, the elements are brought back in series by opening the switching elements Cp1, Cp2, Cp, 2j_1, Cp2j2N-let Cp2N and by closing the switching elements Cs 1, Cs j An alternative of use consists in carrying out the balancing operation while using the battery (ie, while driving or charging). Following the acceptable voltage drop for the traction chain and auxiliary operation, a calculated number of storage elements are selected and removed from the series connection, and then paralleled for balancing. The battery continues to supply power to the traction chain through the storage elements still connected in series. The removal of the elements which must be balanced from the series connection is obtained by opening the switching elements Cs 1. Their paralleling then results from the closing of the switching elements Cp, 21_1, Cp, 21. This is illustrated in FIG. 2 for the paralleling of elements j and j + 1. Note that if two storage elements at non-adjacent locations are to be paralleled (for example, j and j + 2) then all the elements between the elements to be paralleled do not provide any more information. (in this example the element j + 1) in the case where these elements are not also connected in series or in parallel, which is the case in Figure 3. It can then be interesting to parallel all the elements located between the end elements, as illustrated for example in Figure 4 where the central element is connected in parallel. But this last variant has limitations because if the two energetically most interesting elements to balance are located near the opposite ends of the series assembly, it becomes unusable since the voltage drop generated would not be acceptable for the proper operation of the chain of The connection structure shown in FIG. 5 is intended to answer this problem, by making it possible to balance any two elements during the use of the battery (that is to say, when rolling or charge). For this, it is necessary to remove the elements that must be balanced from the serial assembly, while maintaining the integrity of the serial assembly for the other elements. This can be done by arranging branch branches shuntant each desired one or more storage elements within the series assembly, each of its branches carrying a switching element Ch. The removal of an element J is done by the opening of the switching elements Cs, 2j_i, j and the closing of the switching elements Ch j. According to the acceptable voltage drop for the operation of the power train and the auxiliaries, a calculated number of storage elements are thus selected and then removed, then no longer supplying energy, are switched in parallel to achieve their balancing. a previously described manner. On the other hand, the rest of the battery is still in operation and therefore the state of charge of the various storage elements is changing.

In order to reduce the number of switches required, it is possible to provide that each storage element may comprise in series at least one electrochemical cell, or bicell, or modules, or set of modules, in series. However, this solution has the disadvantage of not correcting the imbalances internal branches when they are in parallel. The balancing principle is presented in application to two storage elements each constituted by an electrochemical cell (FIGS. 6 and 7). In a simplified battery pack composed of these two electrochemical cells of the same technology, they are normally in series (Figure 6). Each cell is unique in design. The manufacturing process of the cells does not make it possible to obtain completely identical cells. The ability in particular may differ. Thus two cells in series which are traversed by the same current can see their state of charge evolve differently. The empty voltages of the cells represented by OCV1 and OCV2 depend on the state of charge of the cell. Thus, having states of different charges the voltages U1 and U2 will be different. Once the battery pack is not in use, it is possible to change the connection mode between the cells, and switch from the serial connection to a parallel connection (Figure 7). This is done by the proper connection structure described in this document. The paralleling of these cells is accompanied by an equality of electrical tension which generates the flow of a current from the most charged cell to the cell which is less. Figure 7 illustrates the case where cell 1 is the most loaded. Thus the current ieq will charge the cell 2. Its increasing state of charge, OCV2 also increases and ieq decreases until the cells are balanced in voltage and therefore approximately in state of charge.

To increase the available capacity, a battery pack for use in an electric vehicle often comprises a series assembly of cells assembled together in parallel (see Figure 8). When two cells are assembled in parallel, this is called a bicell. However, it may be the paralleling of a variable number of bicells, or modules, etc. Considering N bicells in series (see Figure 8), the structure of each bicell requires that cells 1 and 2 as well as 2J-1 and 2J and 2N-1 and 2N are always voltage-balanced. For the same reasons as above, the different bicells in series can be at different states of charge and at different voltages Ub1 and UbJ and UbN. The paralleling obtained by the connection structure imposes a voltage equality which generates the flow of a current, which equalizes the states of the charges and consequently the voltages of the cells (see FIG. 9).

Quite similarly, it is possible to extend the principle to the balancing of N modules within each of which at least two cells connected in parallel are connected in series with at least two other cells connected in parallel. . The series assembly of the pack modules is presented in FIG. 10 and their paralleling and balancing, according to the invention, in FIG. 11. It should be noted that the voltage of the module is equal to the sum of the voltages of the bicells. The equality of the voltage across all the cells is not ensured, but only across the modules in parallel. An imbalance in the state of charge within the module is therefore not corrected since the pairs of cells of the module are traversed by the same current. The previously described solution allows balancing circuits with few components. In addition to a low cost, it eliminates a chain of energy transport and therefore losses of conversion efficiency associated with it. Incidentally, it makes it possible to dispense with a precise measurement of the voltage of the cells, therefore the voltage sensors can be replaced by less efficient sensors but less expensive.

The invention has the following advantages: - it is a non-dissipative balancing, which redirects the energy within the battery, from the most charged elements to the least loaded, - it only requires the electronics to drive the switching elements, which reduces losses, it allows balancing even if the battery is not used, and the storage of the battery for long periods in balancing configuration also allows for combat the imbalance effects caused by self-dumping of storage elements.

Claims (15)

REVENDICATIONS1. A method of managing an electric power storage battery comprising a plurality of storage elements for electrically connecting with each other in a series connection, the management method comprising a step of balancing the electrical charges including same: - a selection step, among the plurality of storage elements, 10 at least two storage elements at the terminals of which the electrical voltages are different, - a step of disconnection out of the series connection, the storage elements selected at the selection step; and a step of electrically connecting them in a parallel arrangement of all or part of the disconnected storage elements at the disconnection step. 2. Management method according to claim 1, characterized in that the number of storage elements selected in the selection step is less than the total number of storage elements included in the battery, at least a part of the elements. storage not selected in the remaining selection step connected together electrically in series at the end of the connection step. 3. Management method according to claim 2, characterized in that the storage elements selected in the selection step are located at any location within the series arrangement, adjacent or not. 4. Management method according to claim 3, characterized in that in the case where at least two of the storage elements selected in the selection step are located at non-adjacent locations within the series connection, the storage elements unselected ones implanted in the series connection between said locations are connected, during the connection step, in the parallel connection with the selected storage elements. 5. Management method according to claim 3, characterized in that the connection step comprises closing "branch bypass branches" each configured to shunt at least one of the storage elements selected at the selection step at within the series assembly. 6. Management method according to one of claims 2 to 5, characterized in that in case of use of the battery, the management method comprises a step of charging and / or electric discharge of the storage elements of the battery connected in series after the connection step. 7. Management method according to one of claims 1 to 6, characterized in that the balancing step is performed in case of unused battery without charge and / or electric discharge of any storage element of the battery from outside the battery. 8. Management method according to claim 7, characterized in that the balancing step is such that the number of storage elements selected in the selection step is equal to the total number of storage elements of the battery, and all the storage elements of the battery are connected in parallel with each other following the connection step. 9. Management method according to one of claims 1 to 8, characterized in that the selection of the storage elements in the selection step is based on selection criteria taking into account the allowable voltage drop of the battery and / or a desired dynamics of the balancing and / or a threshold value of the electrical intensity in the parallel connection. 10. Device for managing an electric energy storage battery comprising on the one hand a plurality of storage elements and, on the other hand, a connection structure for electrically connecting the storage elements to each other in a mounting arrangement. series, characterized in that it comprises software and / or hardware means which implement a management method according to any one of claims 1 to 9. 11. Management device according to claim 10, characterized in that the connection structure comprises electrical connections between the storage elements and switching elements arranged on the electrical connections, the electrical connections and the switching elements can be controlled from so that the connection structure can vary between at least a first state in which all or part of the storage elements are electrically connected to each other in a series connection and at least a second state in which all or part of the storage elements are connected electrically between them in a parallel connection. 12. Management device according to claim 11, characterized in that it comprises a control unit generating actuation commands driving the switching elements so as to vary the connection structure from one state to another of a way performing the balancing step. 13. Management device according to one of claims 11 and 12, characterized in that the switching elements are insulated gate field effect transistors "MOSFET". 14. Management device according to any one of claims 10 to 13, characterized in that each storage element of the battery is constituted by a supercapacity or an electrochemical unit cell or a member having at least two such cells electrically connected in parallel. or a module comprising at least two such electrically connected members in series with each other or an assembly comprising at least two such modules electrically connected in series with each other. 15. Motor vehicle comprising a management device according to any one of claims 10 to 14 for controlling the electric energy storage battery supplying an electric traction chain of the vehicle and / or electrical auxiliary devices on board the vehicle.