EP2994341A1

EP2994341A1 - Security system for an accumulator battery module and corresponding method for balancing a battery module

Info

Publication number: EP2994341A1
Application number: EP14723765.5A
Authority: EP
Inventors: Daniel Chatroux; Sébastien CARCOUET; Eric Fernandez
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2013-05-09
Filing date: 2014-05-07
Publication date: 2016-03-16
Also published as: FR3005535B1; WO2014180935A1; FR3005535A1; US20160118819A1

Abstract

The invention concerns a security system for a battery module (1), said system comprising: - at least one battery module (1) having a positive pole (P) and a negative pole (N) and defined by a matrix comprising a first predefined number n of columns, n being greater than or equal to two, and a second predefined number m of lines, m being greater than or equal to two, the matrix being such that: • each column defines an accumulator branch (Brj (j= 1.. n)) having m accumulators (Aij) in series, the accumulator branches (Brj) being linked by the ends of same in parallel and to the poles (P, N) of the battery module (1), and such that • each line of the matrix defines an accumulator stage (Eti), and at least one charge control device (2, 5, 3) connected to the poles (P, N) of the battery module (1), characterised in that: - the battery module (1) further comprises: • a plurality of resistors (Rt) respectively electrically linked to the intermediate point between two accumulators (Aij, Ai+1j) of two adjacent accumulator stages (Eti, Eti+1) and • a third predefined number p of connection nodes (NCi) respectively connected to a set of n resistors (Rt) connected to the intermediate points of the accumulators (Aij, Ai+1j) of the two adjacent accumulator stages (Eti, Eti+1), and in that the charge control device (2, 5, 3) is connected to the set of connection nodes (NCi).

Description

Securing system for a storage battery module and method of balancing a corresponding battery module

The invention relates to electrochemical storage battery modules, for example used in the field of electric and hybrid transport or embedded systems. The invention also relates to a method of balancing such a battery pack module.

The invention can also be applied to supercapacitors.

Hybrid combustion / electric or electric vehicles include in particular high power batteries used to drive an AC electric motor via an inverter. The voltage levels required for such engines reach several hundred volts, typically of the order of 400 volts. Such batteries also have a high storage capacity to promote the autonomy of the vehicle in electric mode.

The electrochemical accumulators used for such vehicles are generally of the lithium-ion type for their ability to store significant energy with a weight and volume contained. In particular, LiFePO4 lithium iron ion-phosphate battery technologies are undergoing significant development due to a high intrinsic safety level, compared to conventional lithium-ion batteries based on cobalt oxide. .

To obtain high powers and storage capacities, several groups of accumulators are placed in series. The number of accumulator stages and the number of accumulators in parallel in each stage vary according to the desired voltage, current, and storage capacity. The combination of several accumulators is called thereafter battery module.

In a known manner, as illustrated in FIG. 1, such a battery module Bat comprises several accumulator stages, for example four stages Eti, Et ₂ , Et ₃ and Et ₄ , connected in series. Each stage comprises for example at least two, for example four, generally similar accumulators, connected in parallel.

The voltage across the four stages is denoted respectively U1, U2, U3 and

U4. In this diagram, the total voltage U between the terminals N and P of the battery module 1 is the sum of the voltages U1, U2, U3 and U4. The current flowing through each accumulator of the fourth stage Et4 is noted respectively II, 12, 13 and 14. The current I generated on the terminal P of the battery module Bat is the sum of currents II, 12, 13 and 14.

The charge of an accumulator results in a growth of the voltage at its terminals. A charged accumulator is considered when it has reached a voltage level defined by the electrochemical process.

If charging is stopped before this voltage is reached, the battery is not fully charged.

It is therefore important to monitor in detail the voltage of each battery during charging and discharging.

Indeed, some battery technologies (NimH, NiCd) naturally clone the voltage at their terminals thanks to a parasitic chemical reaction within the alkaline electrolyte and can continue to be crossed by a current when their high voltage threshold has been reached. . Other accumulators not yet fully charged can continue to be charged by the current. The voltage clipping is then done by internal electrochemical reactions other than the electrochemical reaction of operation of the accumulator and this is accompanied by heat dissipation.

On the other hand other types of technologies such as lithium-ion do not clink naturally. There is no other electrochemical reaction to ensure clipping of the voltage with dissipation of energy. It is imperative to interrupt the current through the accumulator to prevent its deterioration or total destruction.

For lithium-ion accumulators based on Cobalt Oxide, the overcharging of an accumulator can cause its thermal runaway and a start of fire. For a phosphate-based accumulator, an overload results in a decomposition of the electrolyte which reduces its lifetime or can damage the accumulator, but without causing a risk of fire.

In addition, the lithium-ion type accumulators have a minimum voltage below which it is not necessary to go down so as not to degrade the accumulator.

Thus, it is imperative to stop the discharge of the battery module when the least charged battery reaches its low voltage threshold. Conversely, during a load, it must be stopped when the most charged accumulator has reached its high voltage threshold.

However, if charging simply stops when the most charged battery reaches its threshold voltage, other batteries may not be fully charged. The current must then be deflected so that it bypasses the most charged accumulator and continues to charge the other accumulators of the circuit.

Similarly to the discharge, once the weakest battery is discharged, it must eventually bring him energy if we want to continue to discharge the other batteries without damaging the first.

These current deflection and dissipation or power supply functions can be all the more complex or of high power as battery accumulators are dispersed in storage capacity.

In the case of using battery accumulators which do not naturally stop, such as lithium-ion accumulators it is necessary to associate each battery with an auxiliary balancing circuit.

Classically, the paralleling accumulator branches comprising accumulators put in series, lithium-ion type does not naturally stop, are not used because it must be associated with each accumulator a clipping function and that you have to control the load of these. The large number of such circuits results in a high cost and a high impact on the bulk.

One solution consists in using battery modules comprising series of accumulator stages comprising accumulators placed in parallel, as in the example of FIG. 1.

However, if the battery accumulators used to perform this circuit do not naturally cancel, it is necessary to add for each stage an auxiliary balancing circuit and load control, so that all stages can be loaded correctly.

Furthermore, throughout the life of the battery module, some defects may appear on some accumulators of the battery module. A fault on an accumulator usually results in either short-circuiting the accumulator, either by an open circuit or by a large leakage current in the accumulator. It is important to know the impact of battery failure on the battery module. Open or short-circuiting may cause an overall failure of the entire battery module.

In the case of the occurrence of a large leakage current in a battery of a stage, the battery module behaves like a resistor which causes a discharge of the accumulators of the stage considered to zero. The risks of starting fire are low because the energy is dissipated relatively slowly. In lithium-ion technology, the discharge of the accumulators of the stage up to a zero voltage deteriorates them, which implies their replacement in addition to the initially defective accumulator.

When an accumulator forms a short circuit, the other accumulators of the stage are discharged in this accumulator, because of the strong section of the electrical connections between them. This discharge occurs quickly with a dissipation of energy which results in a heating of the accumulator in short circuit and accumulators which discharge in the short-circuit. This can be the cause of a fire start.

This situation presents a great danger with lithium-ion technologies based on cobalt oxide and can be problematic for iron-phosphate lithium-ion technologies if the parallelization concerns a large number of accumulators which add up to high energy that dissipates in the accumulator in short circuit.

Moreover, in a battery module formed by paralleling accumulator branches comprising accumulators placed in series, in the event of a malfunction of an accumulator of a battery branch in series short-circuiting, the tension of the other branches is distributed on the accumulators of the branch in default.

In particular, for standard lithium-ion accumulators based on cobalt oxide, such an overvoltage leads to a cascade failure of the accumulators with a high risk of fire starting. In view of these aforementioned drawbacks, some solutions of the state of the art adopt protections of each accumulator by a fuse in series.

The addition of fuses in series with the accumulators as shown in Figure 1 effectively provide protection against battery failures (short circuits).

The fuse placed in series with the battery in short circuit will interrupt the parasitic discharge of the other three accumulators.

In order to protect the battery pack Bat from the consequences of a short circuit in an accumulator, each battery has a fuse connected to it in series.

Fuse protection works on the principle of melting a metal conductor through which an electric current flows. When an accumulator forms a short circuit, the current flowing therethrough increases substantially and fuses its fuse in series to protect the rest of the battery pack Bat.

However, the individual fuses in series with each accumulator generate a high cost (component and assembly) since these protections are dimensioned for the nominal current of the accumulators.

In addition, the presence of fuses in series between the battery stages adversely affects performance and induces significant losses, particularly disabling for embedded applications. Indeed, these fuses in series with accumulators add an internal resistance to the battery module resulting in additional losses that lower its performance.

In order to remedy these drawbacks, a solution has been proposed in document WO2011 / 003924 making it possible to eliminate the losses induced by a protection system during the normal operation of the battery module, and also making it possible to ensure continuity of service. of the battery module when a battery of the battery module is in short circuit or circuit breaker.

In this document, the battery module comprises at least first and second branches each having at least first and second accumulators connected in series. The battery module further comprises a fuse via which the first accumulators of the branches are connected in parallel and through which the second accumulators of the branches are also connected in parallel. The cut-off threshold of the fuse is sized to open when one of the accumulators is short-circuited.

However, during a quick recharge when the vehicle is stopped by connecting the battery module to the electrical network or during operation of the electric motor as a generator during the driving of the vehicle, significant charging or balancing currents can be applied to the vehicle. accumulators. The fuses connected in the parallel connections can thus be traversed by relatively large currents.

In addition, in case of malfunction it appeared that little current flowed in the accumulators of the stage when they are remote from the accumulator in short circuit. This therefore requires putting fusible wires with relatively low melting currents, for example less than 2A, and therefore relatively resistive (> 50mohms). This is not a problem for weak balancing currents in slow charging but can become more problematic during a quick charge balancing where the currents involved will be of the order of a few amperes. This may cause the melting of the fuse wire or at least fatigue and significant heat losses.

In addition, some fuses can be crossed by the accumulation of charging or balancing currents to several accumulators of the same floor and remote charging connectivity. Some fuses may thus represent a common connection of several accumulators to the balancing circuit. Therefore, the dimensioning of the fuses of the parallel connections may be difficult to ensure both the protection of the accumulators, the continuity of service of the battery module during a malfunction of an accumulator, and the charging of different accumulators .

The life of the fuses can also be reduced by the repeated application of load currents passing through them.

Conventionally, either by direct paralleling of the accumulators or by means of fuses, all the voltages of the accumulators of the same given floor are equal. It suffices then to have a single voltage measurement to know the voltage of each accumulator of the given stage.

The invention aims to at least partially solve these disadvantages of the prior art.

For this purpose, the subject of the invention is a security system for a battery module, said system comprising:

at least one battery module having a positive pole and a negative pole and defined by a matrix having a first predefined number n of columns, n being greater than or equal to two, and a second predefined number m of lines, m being greater than or equal to two, the matrix being such that:

Each column defines a battery branch having accumulators in series, the accumulator branches being connected at their ends in parallel and to the poles of the battery module, and such that

Each line of the matrix defines an accumulator stage, and at least one charge control device connected to the poles of the battery module,

characterized in that

the battery module further comprises:

A plurality of resistors respectively electrically connected to the intermediate point between two accumulators of two adjacent accumulator stages and

A third predefined number p of connection nodes respectively connected to a set of n resistors connected to the intermediate points of the accumulators of the two adjacent accumulator stages, and

in that the load control device is connected to all the connection nodes. The rows of resistors thus make it possible to connect each accumulator stage to a connection node common to all the n resistors of a row of resistors. According to the invention, the voltage measurement at a common node with n resistors provides information on the average voltage of a stage. Indeed, there is no paralleling of the accumulators so that the accumulator voltages of the same given floor are slightly different.

The load control device connected to all the connection nodes can thus monitor the state of charge of all the accumulator stages by tracking their average voltage to the connection nodes. Only one load control device is required for all battery stages.

With this solution it is not necessary to associate with each accumulator a clipping function and to control the charge of the accumulators individually. This reduces the cost of the system and reduces clutter.

This invention thus has the effect of benefiting from the safety of paralleling accumulators in series and the simplicity of balancing systems and monitoring of voltages.

In addition, when the accumulators are similar and at the same state of charge or discharge, in normal operation without fault of a battery, the resistances are not traversed by any current.

Finally, the resistors are simple components making it possible to limit the short-circuit current during a fault of an accumulator. In this way, a higher security is obtained in a simple manner at a lower cost than the solutions of the prior art with fuses for example.

According to one embodiment, said resistors are identical. With identical resistors connecting each accumulator stage to a connection node, the voltage measured at the connection node necessarily corresponds to the average voltage of the accumulator stage. According to one aspect of the invention, the accumulators are lithium iron ion-LiFePO4 type. Accumulators according to LiFeP04 technology generally having an end of charge voltage of the order of 3.6V can withstand an overvoltage before reaching the destruction voltage of the order of 4.5V. Such overvoltage may in particular occur in the event of malfunction with a short-circuited battery.

According to another aspect of the invention, the load control device comprises at least one balancing circuit electrically connected to all the connection nodes.

The balancing circuit connected to the connection nodes can therefore monitor the state of charge of each accumulator stage and control the balance progressively for example as soon as a stage reaches the plateau voltage added to a chosen threshold. This threshold can be increased until reaching the end of charge voltage.

According to a particular embodiment, the second predefined number m of rows of the matrix and the third predefined number p of connection nodes satisfy the following relation: p = m-1. Each row of n resistors is therefore arranged between two stages of accumulators. This reduces clutter and the number of components.

According to one aspect of the invention, the balancing circuit comprises a plurality of balancing resistors respectively connected in series with a switch, the assembly comprising a balancing resistor and a series switch being arranged in parallel with a accumulator stage while being connected to at least one connection node.

According to a first embodiment, the balancing circuit comprises m first equal balancing resistances respectively associated with a battery stage.

According to a second embodiment, the balancing circuit comprises: first balancing resistances respectively in series with a switch and associated with an intermediate stage while being connected to at least one connection node and two second balancing resistors respectively in series with a switch and associated with an extreme accumulator stage being connected to at least one connection node and one pole of the battery module, and a second resistor

Req '= Req + -

balancing device being according to the formula: ⁿ . In the particular case where the first balancing resistances are zero, the balancing circuit comprises:

switches respectively associated with an intermediate stage while being connected to at least one connection node and

EL

two balancing resistances of value ⁿ respectively in series with a switch and associated with an extreme accumulator stage while being connected to at least one connection node and a pole of the battery module.

According to a third embodiment, the system comprises n resistors connected to the terminals of the accumulators of each end stage which are connected to a pole of the battery module, and the balancing circuit comprises a plurality of switches respectively associated with a stage of accumulators.

According to another aspect of the invention, the charge control device comprises an average voltage measuring device electrically connected to the terminals of the battery module and to all the connection nodes and able to measure the average voltages of the stages of the battery. accumulators.

Said control device is for example configured to detect a malfunction of the battery module by monitoring the average voltage across the accumulator stages. It is therefore not necessary to wait for the complete discharge of a stage to detect a malfunction. This detection can be done quickly.

Said control device is for example configured to detect a malfunction of the battery module when the average voltage across the terminals of at least one of said accumulator stages diverges from the average voltages across the other accumulator stages.

Said control device may be configured to detect a malfunction of the battery module when the average voltage across at least one accumulator stage drops and the average voltages of the other accumulator stages increase.

Said control device is for example configured to detect a malfunction of the battery module in case of discharge of at least one accumulator stage.

The control device may comprise a charger of the battery module and the average voltage measuring device may control the charger to stop the charging of the battery module, for example when the average voltages of the stages have to be balanced.

The average voltage meter can still completely shut down the charger when all stages have reached the end of charge voltage.

According to another aspect of the invention, the system comprises at least two battery modules arranged in series, and an isolation device respectively associated with each battery module and comprising a first switch and a second switch. The first switch is arranged in series with the associated battery module and configured to be closed when the associated battery module is operational and open in the event of a malfunction of said battery module, and the second switch is arranged as a bypass of the associated battery module and configured to be open when the associated battery module is operational and closed in the event of a malfunction of said battery module.

Said control device is for example able to apply an opening control signal of the first switch and to apply a closing control signal of the second switch associated with a battery module in the event of detecting a malfunction of said battery module. .

The isolation device makes it easy to isolate one of the battery modules, for example in case of malfunction with a short-circuited battery. The Other battery modules can continue to be used this ensures some continuity of service.

The invention also relates to a method of balancing a battery module of a system as defined above, said method comprising the following steps:

a threshold for triggering the balancing is determined,

the average voltage of the accumulator stages at the connection nodes is monitored,

at least one accumulator stage is detected whose average voltage reaches a predefined plateau voltage added to the determined balancing trip threshold,

the charging of the battery module is stopped when the average voltage of at least one accumulator stage reaches a predefined plateau voltage added to the determined balancing trip threshold,

the average voltages of the accumulator stages are compared with each other,

at least one accumulator stage of lower average voltage than the average voltage of the other accumulator stages is determined, the closing of the switch in parallel with each accumulator stage of higher average voltage is controlled than the stage a lower average voltage accumulator, whereby the accumulators (A) of the higher average voltage accumulator stages are discharged through the balancing circuit, and

- The charge of the battery module is restarted when the equilibrium is reached between the average voltages of all the accumulator stages of the battery module.

According to one embodiment, the determination of the threshold for triggering the balancing comprises the following steps: the difference between the plateau voltage and a predefined end of charge voltage is determined,

said difference is divided by a predefined number n of accumulators in an accumulator stage, the result obtained is said threshold for triggering the balancing.

According to one aspect of the invention, the threshold to be added to the plateau voltage is gradually increased until a predefined end of charge voltage is reached. Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

- Figure 1 is a schematic representation of a system comprising an example of battery and balancing circuit according to the state of the art;

FIG. 2 is a schematic representation of a system comprising a battery module according to the invention;

FIG. 3 is a schematic representation of a system comprising a battery module according to the invention, a balancing circuit, a voltage measuring device and a charger;

FIG. 4 is a schematic representation of the battery module of FIG. 2 on which a balancing current is represented;

FIG. 5 illustrates an exemplary balancing circuit comprising balancing resistors;

FIG. 6a is a schematic representation of a system comprising the battery module of FIG. 4 with the balancing circuit of FIG. 5;

FIG. 6b is a schematic representation of a system comprising the battery module of FIG. 2 with a balancing circuit according to a second embodiment;

FIG. 7a is a schematic representation of a system comprising the battery module of FIG. 2 with a balancing circuit according to a third embodiment; FIG. 7b is a schematic representation of a system comprising a variant of the battery module with a balancing circuit without balancing resistor;

FIG. 8 is a schematic representation of the battery module of FIG. 2 during a malfunction of an accumulator of the battery module;

FIG. 9 schematically illustrates the external currents during the malfunction of an electrochemical cell of the battery module of FIG. 8;

- Figure 10 schematically illustrates the flow of a current from the balancing circuit when a malfunction of an electrochemical cell of the battery module;

FIG. 11 schematically shows an isolated switched battery module;

FIG. 12 schematically illustrates a battery including several modules of FIG. 11 in a normal operating mode; and

FIG. 13 illustrates the battery of FIG. 12 in an operating mode in which one of the modules includes a faulty accumulator.

System

FIG. 2 schematically shows a system comprising an accumulator battery module 1 according to the invention and a charge control device.

The battery module 1 has a negative pole N and a positive pole P of large sections.

The load control device comprises in particular a balancing circuit 2 connected to the P and N poles of the battery module 1. The charge control device may further comprise a charger 3 connected to the battery module 1 to charge the module. Battery 1 (see Figure 3).

Battery module

The invention applies in particular to LiFeP04 lithium-ion iron phosphate type battery modules. An accumulator according to LiFeP04 technology has a large voltage tolerance. Indeed, according to LiFeP04 technology, the maximum voltage is of the order of 4.5V, the margin between the end of charge voltage and the destruction voltage of the battery is large, unlike other Lithium chemistries. Indeed, the voltage specified at the end of charging is 3.6V, so the voltage margin is of the order of IV. For the other chemistries which have an end of charge voltage of the order of 4.2V, the margin is only 0.3V between the end of charge voltage of the order of 4.2V and the maximum voltage of the order of 4.5V.

The battery module 1 is made in the form of a matrix comprising at least two columns and at least two lines, for example n columns and m rows.

The battery module 1 comprises at least two branches Br, (j = 1 ..n) forming the columns of the matrix. Each branch Br comprises at least two accumulators Aij connected in series. And these branches are paralleled by their extremities. The ends of the branches Br, - are connected to the poles P and N.

In addition, branches Br, have the same number of accumulators in series.

A stage of accumulators And; is defined by the set of accumulators which correspond to the same index i at a line of the matrix defining the battery module 1.

More specifically, the battery module 1 comprises a predefined number n of branches Br, and a predefined number m of stages Et ;. The index i is a natural number corresponding to the number of accumulator stages and varies from 1 to m, and the index] is a natural number corresponding to the number of branches and varies from 1 to n.

Each floor And; comprises at least two accumulators Ay, or electrochemical cells. Each floor And; comprises a predefined number n of accumulators Aij. The index j also corresponds to the number of accumulators in a stage Et _; and varies from 1 to n.

Accumulators A are advantageously chosen as similar. In the case of accumulators of unequal quality or different state of charge, it is possible to make a first initial charge slower so as to allow time accumulators to equilibrate. This charge being made only once at the end of manufacture of the battery, its impact can be considered as minor because only time consuming for a battery manufacturer. This is a compromise between the cost and a balancing time and therefore a longer immobilization at the factory outlet.

In the example illustrated in FIG. 2, the first branch Bri includes accumulators A to A _m connected in series. The second branch Br ₂ includes accumulators Ai, ₂ to A _m , ₂ connected in series. The branch Br includes accumulators Aij to A _m j connected in series. The last branch Br _n includes accumulators Ai, n to A _m , _n connected in series.

The battery module 1 therefore comprises at least one matrix of m battery stages Et; and n battery branches Br, in parallel.

In all the columns of the matrix formed by branches Brj, the main current of charging and discharging accumulators passes from the accumulator Ay to the accumulator A _{i +} ij then to A _{i + 2} , j, and so on along the serialization of accumulators Aij, .., Ay,. .. At _mj -, then this current collects at the poles P and N via the electrical connections of large sections.

Each accumulator Ay of the matrix is electrically connected by a link dimensioned for the charging and discharging currents with the accumulator Ai + y.

The battery module 1 further comprises secondary electrical connections provided with resistors Rt between all the accumulators Ay.

More specifically, the battery module comprises a plurality of resistors Rt respectively electrically connected to the intermediate point between two accumulators Ay, Ai + ij of two adjacent accumulator stages And _; , And _{i +} i and a third predefined number of NC connection nodes _; respectively connected to a set of n resistors Rt connected to the intermediate points of the accumulators Ay, A _{i +} ij of two adjacent accumulator stages Et _; , And _{i +} i.

More specifically, the battery module 1 comprises at least one row of n resistors Rt connected to the accumulators Ay, A _{i +} ij of two adjacent accumulator stages Et _; , And _{i +} i.

In the illustrated example, the battery module 1 comprises the predefined number p of rows of resistors Rt. According to the embodiment illustrated in FIG. 1, this third predefined number p_ satisfying the relation (1):

(1) p = m - 1 where m is the number of accumulator stages And _; . Each row of resistors Rt comprises n resistors Rt, which is the same number as accumulators Aij in an accumulator stage Et _; .

The resistors Rt of a row of resistors are respectively electrically connected on the one hand between a first accumulator A and a second accumulator A _{i +} i _j in series of a branch Br, and on the other hand with so-called common connection node NG (i = 1 ..ml) to all n resistances Rt of the row of resistors.

Thus, the set of accumulators Aij a stage And _; have a terminal connected to a common NG connection node through the resistors Rt.

The other terminal of the accumulators Ay can be connected to another common connection node NC; via other respective resistors Rt. When it comes to the extreme accumulator stages Eti and Et _m , the other terminal of the accumulators Aij (j = 1 ..n) and A _mj - (j = 1 ..n) can be connected to a pole P or N of the battery module 1.

Thus, in the example illustrated in FIG. 2, the resistors Rt of the first row of resistors connect the negative terminals of the accumulators Ai j of the first stage Eti to the common connection node NG and, on the other hand, connect the positive terminals of the accumulators A. _2j of the second stage And ₂ to this common NG connection node.

More generally, the resistors Rt of the row of resistors of order i, connect the negative terminals of the accumulators Ay of the stage Et; to the common connection node NG and on the other hand connect the positive terminals of the accumulators A _{i +} ij of the second stage Et _{i +} i to this common connection node NG.

In addition, the load control device is also connected to all the common NG connection nodes.

According to the illustrated embodiment, the balancing circuit 2 is connected to the common connection nodes NG. During a charging or discharging phase, the main current in a branch passes through all the accumulators connected in series in this branch. During such operation, if all the accumulators A are similar and have the same state of charge or discharge, no transverse current flows through the resistors Rt.

The dimensioning of the resistances Rt is defined by a compromise between various parameters on which one wants to act, such as:

- the maximum continuous current accepted in a Br branch,

- the discharge time of a stage And; comprising a faulty accumulator Ay,

the balancing current Ieq (cf FIG. 4) corresponding to the current exchanged by a stage Et _; with the balancing circuit 2,

the balancing time of the accumulators of the same branch Br ,, this being a function of the slow or fast charging mode,

- Easier end of charge detection, this is all the easier as the number of accumulators A in parallel is low.

The dimensioning must therefore be done according to the architecture of the module and accumulators used.

This solution can be realized with resistors Rt of large value (several ohms or even tens of ohms) so as to limit the balancing current between accumulators and thus heating of an accumulator in case of short circuit while having a balancing time compatible with the application.

As an illustrative example, the range of values of the resistors Rt may be of the order of 10Ω to 1kH. The resistors Rt may for example be chosen with a value of the order of 50Ω.

Moreover, the voltage measured at the common node NC; corresponds to the average voltage of accumulators Aj.

For this purpose, the load control device may comprise an average voltage measuring device 5 of the accumulator stages And _; (see Figure 3). This average voltage measuring device 5 is electrically connected to the common nodes NC; to which the accumulator stages Et are respectively connected _; via the resistors Rt and the terminals P and N of the battery module 1.

The invention is distinguished from the state of the art by measuring the average voltage of a given stage while conventionally in the prior art the measurement of the voltage of all the accumulators is required. For this, in the prior art, the paralleling of the accumulators by strong current link or fuses cause all the accumulators of the given stage have the same voltage.

In addition, such a structure makes it possible, in particular for the LiFePO4 type battery modules, to know whether the voltages of the accumulators A are correct and to easily determine a zone of the faulty battery module 1.

As a reminder, the plateau voltage is for example of the order of 3.3V. If the measured average voltage is of the order of this plateau voltage added to a given threshold, for example is of the order of 3.4V, the accumulators are considered to have respectively a minimum voltage equal to this plateau voltage of 3 3V. Indeed, by construction, the dispersion of the accumulators according to the LiFePO4 technology is low, in particular of the order of 10%, so when the average measured voltage is of the order of 3.4V, the accumulators of this stage all have a minimum voltage of the order of 3.3V.

The average voltage Umoy provides information on the voltages of the accumulators of the given floor to 100mV in the example described. A battery balancing strategy will be described later in more detail.

In addition, if an accumulator fails, an average voltage will drop while other average voltages will increase. By measuring the average voltage Umoy of each stage And _; , the balancing circuit 2 can thus detect a failure, for example by noting that a stage discharges or charges differently from the other stages. Since a short-circuited accumulator remains connected in parallel with the other accumulators of the stage, it can be detected that the other accumulators are gradually discharged therein. This makes it possible to quickly detect that an accumulator is in fault. The operation in case of malfunction of an accumulator Ay will be detailed later.

Balancing circuit

The load balancing circuit 2 is electrically connected to each of the stages Eti to Et _m , as previously described by the common nodes NC; and are also connected to the N and P terminals of the battery module 1.

The balancing circuit 2 is configured to implement load balancing of the accumulators j of these stages Et _; , depending on the monitoring of their state of charge. A balancing strategy will be described in more detail later.

The balancing circuit 2 comprises a predefined number of balancing resistors Req.

More precisely, the balancing circuit 2 comprises, according to a first embodiment illustrated in FIGS. 5 and 6a, a first balancing resistor Req in series with a switch 4 for each accumulator stage And;

The value of the first balancing resistors Req is chosen as a function, in particular, of the performance of the accumulators used, the desired balancing time, and the dissipation that may be admitted in the resistor, the electronic support, and more generally the battery module. .

These first balancing resistors Req can have a value of the order of 10 ohms.

The first resistors Req and switches 4 associated in series arranged in extreme position can be connected firstly to a terminal P or N of the battery module 1 and secondly to NC common connection node ;.

The balancing current Ieq is defined by the first balancing resistors Req but also the resistors Rt which when the switches 4 are closed are in series with the first balancing resistors Req. For the intermediate stages Et ₂ to Et _m _i the equivalent resistance of the circuit corresponds to a first balancing resistor Req added twice to a resistor Rt divided by the number n of resistors Rt, according to relation (2):

(2) Equivalent resistance for an intermediate stage =

Indeed, in the event of closure of the switch 4 associated with an intermediate stage the current would pass through all the resistors Rt connected to the first terminals of the accumulators of this stage, by the first balancing resistor Req, then again by the resistors Rt connected to the second terminals of the accumulators of this stage.

For the extreme stages Eti and Et _m, the equivalent resistance corresponds to a first balancing resistor Req added to a resistor Rt divided by the number n of resistors Rt, according to relation (3):

Req + -

(3) Equivalent resistance for an extreme stage = ⁿ .

The equivalent resistance is therefore lower for the extreme stages Eti and Et _m , and the current is therefore stronger.

In this case, in order to obtain equivalent equilibrium currents Ieq, it is possible, according to a second embodiment illustrated in FIG. 6b, to provide in the balancing circuit 2 two second balancing resistors Req 'for the extreme stages. Et and Et _m , the second balancing resistors Req 'being according to equation (4) equal to a first resistor Req added to a resistor Rt divided by the number n of resistors Rt:

Req '= Req + -

(4)

Thus, according to the second embodiment visible in FIG. 6b, the balancing circuit 2 comprises a first balancing resistor Req in series with a switch 4 for each intermediate stage of accumulators Et ₂ to Et _m _i, and for the extreme stages Eti and Et _m a second balancing resistor Req 'also in series with a switch 4. It is also possible to provide an alternative embodiment making it possible to eliminate at least some of the balancing resistors, in particular the first balancing resistors Req of the embodiment illustrated in FIG. 6b, since the resistors Rt can serve as resistor balancing, as shown in Figure 7a.

This has the advantage of distributing the power to be dissipated in the balancing in n resistors instead of just one. This can help reduce the full cost of the solution by using SMD resistors (for surface mounted component). This solution is also suitable for balancing requiring large powers.

In particular according to the embodiment of FIG. 7a, the balancing circuit

2 comprises two balancing resistors at the end stages Eti and Et _m respectively in series with a switch 4, and for each intermediate stage of accumulators Et ₂ to Et _m _i, an intermediate switch 4. Intermediate switches 4 are respectively connected to a common node NC; connected to the accumulators of an intermediate stage Et ;.

In this case, in order to obtain equivalent equilibrium currents Ieq, the value of the first balancing resistors associated with the intermediate stages being zero, it is possible in the balancing circuit 2 for the two balancing resistors to be equalized.

EL

be of the order of ⁿ for the extreme stages Eti and Et _m

Finally, according to another variant illustrated in fîgure7b, the two balancing resistors associated with Eti end stages and _m and the variant of Figure 7a were also removed and n Rt resistors are distributed on the one hand in connection with the terminals of the accumulators Aij and A _mj - extreme stages Eti, and _m and secondly with a pole P or N of the battery module 1.

According to the illustrated example, n resistors Rt are connected to the terminals of the accumulators Ay of the first stage Eti and to the pole P, and n other resistors Rt are connected to the terminals of the accumulators A _mj - of the last stage Et _m and to the pole N.

With such an arrangement, each accumulator Aj is connected to a resistor Rt at each of its terminals. The additional resistors Rt connected to the pole P are connected to a common node NCo and the additional resistors Rt connected to the pole N are connected to a common node Nc _m . In this case the third predefined number satisfies the following relation (5):

(5) p = m + 1.

The fact of coming to place the resistors Rt, as close as possible to the accumulators Aj makes it possible to have a source of heat that can be used to warm them if the battery module is used in cold weather. This function can be used to warm the battery module or maintain its temperature to optimize its performance.

The resistors Rt make it possible to keep the accumulators Ay in temperature or to heat them in cold weather, for example by a transfer of heat to the two terminals of the accumulators Aj.

Moreover, according to this variant all the accumulator stages Eti to Et _m are identical.

Balancing strategy

A balancing strategy according to the invention consists in waiting for the average voltage Umoy of a stage Et; reaches a plateau end voltage, for example of the order of 3.3V plus a threshold chosen for a storage battery 1 according to LiFeP04 technology. For this, the measuring device 5 can measure the average voltage Umoy of a stage Eti.

When this end of plateau voltage, for example 3.3V, added to a trigger threshold of the selected balancing, is reached, a charge stop control signal coming for example from the measuring device 5 is transmitted to the charger 3 to stop the charging of the battery module 1 and control the balancing between the stages Eti to Et _m . In this case the average voltage measuring device 5 is able to control the charger 3.

As a reminder, the voltage measured at the common node NC; represents the mean voltage Umoy of the accumulators j (j = 1 ..n) of the stage Et _; given. For accumulators according to LiFePO4 technology, the plateau corresponding to a charge of between 10% and 90% is of the order of 3.3V. If an imbalance appears, it will therefore be between this plateau voltage of 3.3V and the end of charge voltage generally of the order of 3.6V.

The maximum difference is therefore of the order of 0.3V. This maximum deviation is divided by the number n of branches Br, of the battery module 1 and becomes 0.3V / n.

This value of 0.3V / n can be the starting point for a preferred balancing solution to set the balancing trip threshold to be added to the 3.3V plateau voltage to stop the load and start the load. balancing. According to the example described, it is chosen to stop the charge as soon as the measured average voltage reaches 3.3V + 0.3V / n, for example 3.36V for a battery module 1 comprising five Br branches.

The mean voltages Umoy of the accumulator stages Et are compared _; between them, so as to determine at least one stage of accumulators And; average voltage lower than the average voltage of the other battery stages.

The switches 4 of the balancing circuit 2 associated with the stages of higher voltage, that is to say of average voltage higher than the determined accumulator stage of lower average voltage, are closed.

The accumulators of the higher average voltage storage stage or stages are discharged into the balancing circuit 2, for example through a resistor

EL

Balancing Req or Req 'or ⁿ .

The discharge of the accumulators of the stage being balanced is represented by the balancing current leq flowing from the accumulator stages to the balancing circuit 2 to discharge for example in the balancing resistors Req or

EL

Req 'or ⁿ .

The balancing current in each accumulator j corresponds to the current

leq

balancing leq divided by the number n of branches Br ,, ie. The balancing current in each accumulator is therefore very low. In the case where the balancing current Ieq is of the order of 250mA, the balancing current

ieq

passing through each accumulator A of a stage Eti is therefore of the order of 250 mA / n or a few tens of mA at the most for ten accumulators j in parallel.

A transverse current Ity flows through the resistors Rt.

This operation can be done for several floors at the same time.

However, with a balancing circuit according to the variant shown in Figure 7, it is preferable not to close two successive switches. Indeed, two switches closed in series would change the balancing current. In this case the resistors Rt would be crossed by a double current. To remedy this, it must be taken into account in the design of the resistors Rt to allow the circulation of a higher current.

One variant is to provide sequential balancing of two stages of successive accumulators.

When the average voltage Umoy accumulators A of a stage And; given no longer varies over time, the floor Et; is balanced.

The balancing operation is repeated until the average voltages of the higher voltage stages reach the average voltage of the lower voltage stage.

When the equilibrium is reached between the mean Umoy voltages of the accumulator stages And; the charge of the battery module 1 starts again.

The threshold chosen, can be gradually increased to accelerate the balancing. Thus, as the stage equilibrates, the measured average voltage value can be raised to 3.6V and thus obtain a complete load at 100% of the stage. It is possible in the example described to have a threshold evolving in this way: 3.36V-3.40V-3.45V-3.50V-3.55V-3.60V.

The final charge stop is done as an example when all stages are at

3.6V. A final charge stop threshold of less than 3.6V can be chosen, for example between 3.3V and 3.6V

Dysfunction

The voltage measuring device 5 can determine the presence of a faulty accumulator by identifying a stage at the terminals of which the voltage varies abnormally with respect to the other stages, either during a charge or during a discharge.

It is also possible to identify a stage containing a faulty accumulator from a large variation in its discharge speed or its voltage level since it gradually discharges.

In the event of accidental short-circuiting of a battery A of a branch Br ,, the neighboring batteries will inject a current into the short-circuited battery which will be limited by the resistors Rt. accumulator forms a short circuit, the other accumulators of the stage are discharged in this accumulator, because of the strong section of the electrical connections between them.

In the example of FIGS. 8 and 9, the accumulator A ₃ , 3 suffers a malfunction in short circuit.

The neighboring accumulators will inject a current into the battery A _{3; 3} in short circuit.

Due to the presence of the resistors Rt, the currents between the branches are weak because limited by the resistors Rt. The use of resistors Rt thus makes it possible to protect the accumulators j simply and at a lower cost.

More specifically, following the appearance of the malfunction, due to the presence of the resistors Rt, the transverse load currents from neighboring accumulators are relatively limited. In the neighboring branches of the faulty accumulator A ₃ , 3 (shown in bold in FIG. 8), the current is limited

Vacc

at a value close to ₂ R (where Vacc is the voltage of an accumulator, R the value

Vacc

a resistance Rt). The current is limited to ^ in the accumulator A _{3; 3} in default. This current is low, for example less than 100mA, which will help to discharge the stage Et3 containing the faulty accumulator A _{3; 3} in a very slow manner.

Thus, the overcurrent is limited in amplitude and the battery A _{3; 3} in default only dissipates a small amount of energy from its neighbors. It is not likely to overheat violently. The risk of fire starting is eliminated or greatly minimized.

Subsequently, the faulty stage Et3 discharges slowly and completely into the short-circuited accumulator A _{3; 3} .

Furthermore, it is considered that the accumulators A respectively have a voltage of the order of the plateau voltage, or 3.3V, in normal operation. In the case of faulting of the accumulator A _{3; 3} , the measured average voltage Umoy of the stage Et3 will fall by a value corresponding to the plateau voltage, ie 3.3V, divided by the number n Br branches, five in the example of Figures 8 and 9,

3.3 V

that is ₅ . Thus, in this example, the average voltage Umoy of the stage Et3 comprising the accumulator A _{3; 3} in default will be of the order of 2.64V (see Figure 9).

Moreover, in normal operation, a branch Br has a voltage of the order of the plateau voltage 3.3V multiplied by the number m of stages Et, therefore in the example illustrated with five stages Et _; the voltage of a branch Br is of the order of 3.3 V x 5 ₅ or 16.5V.

The branch Br ₃ presenting the battery A _{3; 3} in default will drop by a value of the order of the battery voltage of the accumulators, here 3.3V, ie from 16.5V to 13.2V.

The branch Br ₃ having its voltage dropping from 16.5V to 13.2V a large current I flows through the ends (see Figure 9). The current flowing in the transverse branches contributes to recharge the accumulators in series with the faulty accumulator by the external connections of the battery module 1 as shown in FIG. 9.

This transient current thus distributes the plateau voltage on the accumulators in series with the one in default by recharging them.

This overvoltage at the level of the healthy accumulators in series with the faulty accumulator depends on the number of accumulators in series and can therefore be strongly decreased if the number of accumulators is large, the overvoltage is of the order of the plateau voltage divided by the number of healthy accumulators in series with the faulty accumulator according to relation (6):

Uplateau

(6) Motor surge on- ⁱ _m _ ^ where Uplateau is the plateau voltage, here 3.3 V, and m is the number of stages Et; .

This will therefore contribute to reload the remaining healthy accumulators in the Br ₃ branch. More precisely, in the example of FIGS. 8 and 9 with five stages Et, there remain four healthy accumulators in the branch Br ₃ comprising the faulty accumulator A ₃ , 3. These remaining four accumulators are distributed so the plateau voltage of the order of 3.3V. Thus, each of the remaining accumulators increases

3,3 ^

a voltage of the order of ₄ , or 0.825V. The remaining healthy accumulators thus have a voltage of the order of 4.125V. This is possible with LiFeP04 technology accumulators that accept a wide voltage range before electrolyte degradation, which only occurs above 4.5 V.

Thus, the measuring device 5 measures a voltage which has fallen with respect to the plateau voltage, for example here 2.64V, for the stage Et ₃ comprising the accumulator A ₃ , 3 in error while it measures a average voltage which has increased on the stages remaining for example here 3,465V corresponding to the average of four accumulators at 3,3V and an accumulator in series with the faulty accumulator A _{3; 3} to 4,125V.

This fall in the average voltage of one stage while the average voltage of the other stages increases allows instantaneous detection of the internal short circuit.

Subsequently, the accumulators of the branch Br ₃ comprising the accumulator A _{3; 3} in default and having an overvoltage as explained above are discharged in the adjacent accumulators of the stage concerned. Thus, apart from the stage Et ₃ comprising the faulty accumulator discharging completely, the other stages progressively reach a voltage close to the plateau voltage at 3.3V.

In conclusion, it is easy to detect the presence of a fault by measuring the average voltages at the common nodes by detecting a variation in the voltage average on the common knot. This is all the easier as the number of cells in parallel is low.

Another detection mode may be to observe the discharge of the accumulators in parallel in the faulty accumulator.

The fault of a given accumulator will have the consequence on the whole of the battery module 1, a complete discharge of the stage where appeared the defect in a time dependent on the number of cells in parallel and the level of the current limited by the Resistors Rt. Nevertheless this discharge according to the dimensioning of the resistors can be very slow, in particular of the order of several hours which has the effect of being able to continue to use the battery module 1.

It may even be possible to perform several charge or discharge cycles before either isolating the battery module 1 or immobilizing the vehicle to repair it.

In addition, it remains possible to balance whether the current flowing through the resistor Rt connected to the faulty accumulator A _{3; 3} is smaller than a current F coming from the balancing circuit 2. With reference to FIG. 10, the current of discharge from the accumulators of the stage Et3 comprising the faulty accumulator A3 may be completely or partially compensated by the current F coming from the balancing circuit 2, according to the dimensioning of the balancing resistors Req, Req '.

This makes it possible to prevent the adjacent accumulators of the faulty accumulator

A3, 3 do not discharge in the latter.

Drums

FIG. 11 shows a switched module, that is to say a battery module 1 as defined previously associated with a first power switch 6 and a second power switch 7.

The first switch 6 is arranged in series with the battery module 1.

The second switch 7 is arranged in parallel with the battery module 1.

The switches 6 and 7 may be MOSFET transistors, which can easily be appropriately sized at a relatively low cost. The control device is able to control the closing and opening of the switches 6, 7. The switches 6, 7 form an isolation device 8 of the associated battery module 1.

In normal operation of the battery module 1, the first switch 6 is configured to be closed and the second switch 7 is configured to be open.

To isolate a battery module 1, the opening of the first switch 6 is controlled and the closing of the second switch 7 is controlled.

Furthermore, a storage device also called battery, for example whose nominal voltage is for example greater than 100V, generally comprises several battery modules 1 connected in series as shown in Figure 12.

The battery has two + and - power output poles.

Each battery module 1 is as previously defined with several accumulator stages Et _; in series defining several branches Br, in parallel and is associated with two power switches 6, 7.

In the configuration illustrated in FIG. 12, the battery modules 1 are all operational. Consequently, their first associated switches 6 are closed and their associated second switches 7 are open, so that the battery modules 1 are connected in series.

In the case where an accumulator fails in one of the battery modules 1, the control device can advantageously command short-circuiting this battery module 1 to ensure continuity of service of the rest of the battery.

In particular, in the case where the accumulator stage Et _; including the faulty battery is completely discharged it is better to isolate it to continue to use the rest of the battery. The principle is to isolate a faulty battery module 1.

To do this, with reference to FIG. 13, when the control device detects a malfunction as explained above by monitoring the average voltages of the stages Et, the first switch 6 is open and kept open in order to isolate the module automatically. battery 1 in case of malfunction. The closing of the second switch 7 is controlled.

The battery can be used in a degraded way ensuring continuity. Thus, the security system as described above makes it possible to obtain lithium-ion batteries tolerant to the short circuit or open circuit failure of an accumulator, provided with balancing circuits to maximize the life of the accumulators Aj, with the advantage of minimizing the number of circuits balancing and monitoring the high and low voltages of all accumulators.

For this purpose, the resistors Rt connect the accumulators of a stage to a common connection node NG on which the average voltage Umoy of the stage can be measured.

Concerning balancing, this solution goes against the prejudices in the technical field of battery balancing because the monitoring is done by monitoring the average voltage at the common node and not by measuring the voltage of each accumulator, and that the skilled person would consider that this solution does not allow a balancing between the accumulators in a simple way.

The detection of a faulty accumulator can take place instantaneously without having to wait for the complete discharge of the accumulator stage comprising the accumulator by detecting a variation of the average voltage at the common node, for example a fall in the average voltage of one stage while the tensions of the other floors increase.

Moreover, the resistors Rt are simple components making it possible to limit the current at a lower cost in order to protect the accumulators in the event of a short circuit in particular.

Another advantage is the concept of security of this solution. By using resistors Rt of relatively large values, the direct current is limited. As a result, the opening of the vent of the faulty accumulator will be at low current but also at low temperature. This vent has the function of avoiding the formation of pressure when the battery temperature increases. This therefore contributes to not increasing even more the pressure within the accumulator and therefore to a less violent vent opening.

Finally, the distribution of the resistors Rt within the battery module 1 ensures a better heat distribution. In particular, the plurality of resistors Rt makes it possible to heat up or maintain the temperature of the accumulators A of the battery module 1, especially when used in cold weather.

Claims

Battery module (1) security system, said system comprising: at least one battery module (1) having a positive pole (P) and a negative pole (N) and defined by a matrix having a predefined first number n of columns, n being greater than or equal to two, and a second predefined number m of rows, m being greater than or equal to two, the matrix being such that:

Each column defines a branch (Br, ₀ = i .. _n) ) of accumulators having m accumulators (Ay) in series, the branches (Br, -) of accumulators being connected by their ends in parallel and to the poles ( P, N) of the battery module (1), and such that

Each line of the matrix defines an accumulator stage (Et _; ), and at least one load control device (2, 5, 3) connected to the poles (P, N) of the battery module (1), characterized in that: the battery module (1) further comprises:

• a plurality of resistors (Rt) respectively electrically connected to the intermediate point between two accumulators (Ay, Ai + ij) of two adjacent floors of accumulators _(Et;, and _{i +} i) and

• a third predetermined number p of connecting nodes _(NC;) respectively connected to a set of n resistors (Rt) connected to intermediate points of the accumulators (Ay, A _{i +} ij) of the two stages of adjacent batteries _(Et;, and _{i +} i), and in that the load control device (2, 5, 3) is connected to all the connection nodes (NG).

2. System according to claim 1, wherein said resistors (Rt) are identical.

3. System according to one of claims 1 or 2, comprising lithium-ion batteries LiFePO4 iron phosphate.

4. System according to any one of the preceding claims, wherein the load control device comprises at least one balancing circuit (2) electrically connected to all the connection nodes (NC _; ).

5. System according to any one of claims 1 to 4, wherein the second predefined number m of rows of the matrix and the third predefined number p of connection nodes (NG) verify the following relation \ p = m - l

6. System according to claims 4 and 5, wherein the balancing circuit (2) comprises a plurality of balancing resistors (Req, Req ') respectively connected in series with a switch (4), the assembly comprising a balancing resistor (Req, Req ') and a switch (4) in series being arranged in parallel with an accumulator stage (Et _; ) while being connected to at least one connection node (NO).

7. System according to claim 6, wherein the balancing circuit (2) comprises m identical first equalizing resistances (Req) respectively associated with an accumulator stage (Et, -).

8. System according to claim 6, wherein the balancing circuit (2) comprises:

first balancing resistors (Req) respectively in series with a switch (4) and associated with an intermediate stage (Et ₂ , ..., and _m _i) connected to at least one connection node (NC ₂ _ ... N _m ₂₎ and

two second balancing resistors (Req ') respectively in series with a switch (4) and associated with an extreme accumulator stage (Eti, and _m ) connected to at least one connection node (NCi, NC _{m -} i) and a pole (P, N) of the module of battery, and wherein a second balancing resistor (Req ') is according to Rt

Req '= Req- \

formula: ⁿ .

9. System according to claim 4, comprising n resistors (Rt) connected to the terminals of the accumulators (A ... Ai, n; A _m i ... A _m , _n ) of each extreme stage (Eti, and _m ) which are connected to a pole (P, N) of the battery module (1), and wherein the balancing circuit (2) comprises a plurality of switches (4) respectively associated with an accumulator stage (Et _; .

The system of any of the preceding claims, wherein the load control device comprises a medium voltage measuring device.

(5) electrically connected to the terminals of the battery module (1) and to all the connection nodes (NG) and able to measure the average voltages (Umoy) of the accumulator stages (Et;).

11. System according to claim 10, wherein said control device is configured to detect a malfunction of the battery module (1) by monitoring the average voltage (Umoy) across the accumulator stages (Et _; ).

12. System according to the preceding claim, wherein said control device is configured to detect a malfunction of the battery module (1) when the average voltage (Umoy) across at least one of said battery stages diverges from average voltages (Umoy) at the terminals of the other stages of accumulators (Et _; ).

13. System according to the preceding claim, wherein said control device is configured to detect a malfunction of the battery module (1) when the average voltage (Umoy) across at least one accumulator stage drops and the average voltages (Umoy) other accumulator stages (Et _; ) increase.

14. System according to any one of the preceding claims, wherein said control device is configured to detect a malfunction of the battery module (1) in case of discharge of at least one accumulator stage (Et;).

15. System according to any one of the preceding claims, comprising: at least two battery modules (1) arranged in series, and

an isolation device (8) respectively associated with each battery module (1) and comprising a first switch (6) and a second switch (7),

The first switch (6) being arranged in series with the associated battery module (1) and configured to be closed when the associated battery module (1) is operational and open in the event of malfunction of said battery module (1), and

• the second switch (7) being arranged in parallel with the associated battery module (1) and configured to be open when the associated battery module (1) is operational and closed in the event of malfunction of said battery module (1).

16. System according to the preceding claim, wherein said control device is adapted to apply an opening control signal of the first switch (6) and to apply a closing control signal of the second switch (7) associated with a module. battery (1) when a malfunction of said battery module (1) is detected.

A method of balancing a battery module (1) of a system according to any one of claims 6 to 9, comprising the steps of:

- determining a balancing tripping threshold, - the average voltage is monitored (Umoy) stages accumulators _(Et;) to the connecting nodes _(NC;), at least one accumulator stage (Et;) is detected whose average voltage (Umoy) reaches a predefined plateau voltage added to the determined balancing trip threshold, the charging of the battery module (1) is stopped when the voltage mean (Umoy) of at least one accumulator stage (Et _; ) reaches a predefined plateau voltage added to the determined balancing trip threshold,

the average voltages of the accumulator stages (Et _; ) are compared with each other,

- determining at least one stage of accumulators _(Et;) of lower average voltage than the average voltage of the other stages of accumulators, it controls the closure of the switch (4) in parallel of each stage accumulator ( And _; ) of higher average voltage than the accumulator stage (Et _; ) determined lower average voltage, so that the accumulators (Aj) accumulator stages (Et _; ) of higher average voltage are discharged through the balancing circuit (2), and

- The charging of the battery module (1) is restarted when equilibrium is reached between the average voltages (Umoy) of all the accumulator stages (Et _; ) of the battery module (1).

The method according to claim 17, wherein the determination of the threshold for triggering the balancing comprises the following steps: determining the difference between the plateau voltage and a predefined end of charge voltage, said difference being divided by a number predefined n of accumulators (Aj) in an accumulator stage (Et _; ), the result obtained is said trigger threshold of the balancing.

19. The method according to claim 17, wherein the threshold to be added to the plateau voltage is gradually increased until a predefined end of charge voltage is reached.