EP2567443A2

EP2567443A2 - Balancing system for power battery and corresponding load balancing method

Info

Publication number: EP2567443A2
Application number: EP11718362A
Authority: EP
Inventors: Laurent Garnier; Daniel Chatroux; Matthieu Desbois-Renaudin
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2010-05-05
Filing date: 2011-05-04
Publication date: 2013-03-13
Also published as: US20130076310A1; FR2959887B1; FR2959885A1; JP2013530665A; FR2959885B1; FR2959887A1; CN103069682A; WO2011138381A2; WO2011138381A3; KR20130073915A

Abstract

The present invention relates to a load balancing system for power battery (1) comprising at least two stages (11) of accumulator(s) placed in series, characterized in that said balancing system comprises at least one flyback converter (15) comprising: a transformer (21) with: at least one primary winding (23) configured so as to be connected to the terminals of a stage (11) of said power battery (1), and a secondary winding (25) configured so as to be connected to an auxiliary battery (5) whose voltage is below the voltage of said power battery (1), and for each stage (11), an associated switch (27) connected to a primary winding (23) and to the negative terminal (-) of the stage (11). The invention also relates to a method of load balancing for the power battery (1) by transferring energy to the auxiliary battery (5).

Description

Balancing system for power battery and corresponding load balancing method

The invention relates to a load balancing system for electrochemical accumulator power batteries and a corresponding load balancing method.

Such a battery can be used in particular in the field of electric transport, hybrid and embedded systems. The invention particularly relates to lithium-ion (Li-ion) type batteries suitable for such applications, because of their ability to store high energy with a low mass. The invention is also applicable to super-capacitors.

An electrochemical accumulator has a nominal voltage of the order of a few volts, and more precisely 3.3 V for Li-ion batteries based on iron phosphate and 4.2 V for a Li-ion technology based on cobalt oxide. If this voltage is too low compared to the requirements of the system to be powered, several accumulators are placed in series. It is also possible to have in parallel each accumulator associated in series, one or more accumulators in order to increase the available capacity and thus to provide a higher current and power. The accumulators associated in parallel thus form a stage. A stage consists of at least one accumulator. The stages are put in series to reach the desired voltage level. The combination of accumulators is called a storage battery.

The charging or discharging of an accumulator results respectively in a growth or a decrease in the voltage at its terminals.

A charged or discharged accumulator is considered when it has reached a voltage level defined by the electrochemical process. In a circuit using multiple accumulator stages, the current flowing through the stages is the same.

The level of charge or discharge of the stages therefore depends on the intrinsic characteristics of the accumulators, namely the intrinsic capacitance and the parallel and parallel parasitic internal resistances of the electrolyte or contact between the electrodes and the electrolyte. Voltage differences between the stages are therefore possible due to the manufacturing and aging disparities of the accumulators. For a battery of Li-ion technology, a voltage too high or too low, called threshold voltage, can damage or destroy it. For example, the overloading of a Li-ion battery based on Cobalt Oxide can cause its thermal runaway and a fire start. For a phosphate-based Li-ion battery, overcharging results in decomposition of the electrolyte which decreases its life or can damage the battery.

An excessively deep discharge that leads to a voltage below 2 V, for example, causes, among other things, an oxidation of the current collector of the negative electrode when the latter is made of copper and therefore a deterioration of the accumulator.

Consequently, the monitoring of the voltages at the terminals of each accumulator stage is obligatory during charging and discharging for a question of safety and reliability. A so-called monitoring device in parallel with each stage ensures this function.

The purpose of the monitoring device is to monitor the state of charge and discharge of each accumulator stage and to transmit the information to a control circuit in order to stop charging or discharging the battery when a stage has reaches its threshold voltage.

However, on a battery with several accumulator stages arranged in series, if the charge is stopped when the most charged stage reaches its threshold voltage, the other stages may not be fully charged. Conversely, if the discharge is stopped when the most discharged stage reaches its threshold voltage, the other stages may not be fully discharged. The charge of each accumulator stage is therefore not exploited, which represents a major problem in transport and embedded applications with high autonomy constraints. To overcome this problem, the monitoring device is generally associated with a balancing system.

The balancing system has the function of optimizing the charge of the battery and thus its autonomy by bringing the accumulator stages placed in series to an identical state of charge and / or discharge.

There are two categories of balancing systems, the balancing systems said energy dissipation, or so-called energy transfer.

With energy dissipation balancing systems, the voltage across the stages is standardized by diverting the load current from one or more stages that have reached the threshold voltage and dissipating the energy in a resistor. As a variant, the voltage across the stages is standardized by discharging one or more stages having reached the threshold voltage.

However, such energy dissipation balancing systems have the major disadvantage of consuming more energy than necessary to charge the battery. Indeed, it is necessary to discharge several accumulators or to divert the charge current of several accumulators so that the last accumulator or batteries a little less charged finish their load. The energy dissipated can therefore be much greater than the energy of the charge or charges to be completed. In addition, they dissipate excess energy in heat, which is not compatible with the integration constraints in the transport and embedded applications, and the fact that the life of the accumulators drops sharply when the temperature increases. 'Student.

Energy transfer balancing systems for their part exchange energy between the accumulator battery or an auxiliary energy network and the accumulator stages.

Energy transfer can be either unidirectional, from the battery to the floors or floors to the battery, or bidirectionally, from the battery to the floors and floors to the battery or from adjacent floor to floor .

With regard to bidirectional transfer, in adjacent stage-level balancing systems, the energy travels a number of devices substantially equal to the distance of the cells to be balanced. This results in the two major drawbacks of these devices, namely the need for a long time to balance a battery and the low efficiency of the energy transfer because of the cumulative losses of the devices solicited.

Balance systems for transferring energy from the stages to the battery and / or the battery on stages solve these problems. However, for reasons of implementation complexity, such systems are little or not used. With regard to the unidirectional transfer, for example CN1905259 discloses a device for transferring energy from the stages to the battery and which uses an accumulator inductance as a storage element. However, this device does not opt for optimized energy transfer for balancing batteries in transport and embedded applications. Indeed, the end of charge of a battery is determined by the last stage which reaches the threshold voltage. To end the charge of a battery, the energy is taken from one or more stages and it is restored to all stages. When one or more accumulator stage (s) is or are slightly less charged, the energy is therefore not transferred in priority to the latter or those who need it or to it, but also to or the stages at which the energy is taken. Balancing therefore requires taking energy from all stages at the end of charging to avoid charging at too high a voltage. Balancing is therefore high losses because of the number of large converters in operation. In addition, the accumulators already at the end of the load are crossed by non-useful AC or DC current components.

The invention therefore aims to provide an improved balancing system does not have these disadvantages of the state of the art.

To this end, the subject of the invention is a load balancing system for a power battery comprising at least two accumulator stages (s) placed in series, each accumulator stage (s) comprising at least one accumulator, characterized in that said balancing system comprises at least one flyback converter comprising:

- a transformer with:

At least one primary winding configured to be connected to the terminals of an accumulator stage (s) of said power battery, and

A secondary winding configured to be connected to an auxiliary battery whose voltage is lower than the voltage of said power battery, and

- for each accumulator stage (s), an associated switch connected to a primary winding of said transformer and the negative terminal of the accumulator stage (s), and in that said system further comprises:

a device for monitoring the voltage at the terminals of said accumulator stages, and

a device for controlling said flyback converter comprising at least one processing means for:

• receive the voltage information of said monitoring device, and

• when at least one stage has a voltage greater than the voltage of the other battery stages (s), control the closing of at least one switch associated with an accumulator stage (s) and the energy transfer of said stage to said auxiliary battery, so as to balance the charge of the accumulator stages.

The balancing system may further include one or more of the following features, alone or in combination:

said system comprises a predefined number of flyback converters respectively associated with a predefined number of modules in series of said power battery, said modules comprising accumulator stages (s) placed in series,

said system comprises a common flyback converter connected to a predefined number of modules in series of said power battery, said modules comprising accumulator stages connected in series,

said system comprises, for each accumulator stage (s), a blocking diode connected by its anode to the primary winding of the transformer, and connected by its cathode to the associated switch,

the blocking diode is a Schottky diode,

said system comprises for each accumulator stage (s) a diode and a transistor in parallel, such that the diode is connected by its anode to the primary winding of the transformer and connected by its cathode to the associated switch of the stage d 'Accumulators),

the switches of the at least one flyback converter are controlled from common way by said control device so as to be closed at the same time when at least one accumulator stage (s) has a voltage greater than the respective voltages of the other accumulator stages (s), the switches of said at least one flyback converter are individually controlled by said control device so as to control the closing of the switch associated with an accumulator stage (s) whose voltage is greater than the respective voltages of the other accumulator stages (s), said device control device comprises at least one processing means for

• calculate for each accumulator stage, a closing time of the associated switch from the determined charge rate, and

• control the closing of the switches respectively during the associated closing times,

said at least one flyback converter is sized for power transfer from the power battery to the auxiliary battery so as to supply the auxiliary battery,

said system is configured for load balancing the accumulator stages (s) of a lithium-ion power battery,

said system is configured for load balancing accumulator stages (s) of a power battery powering the engine of an electric and / or hybrid motor vehicle.

Said balancing system may also further comprise one or more of the following characteristics, alone or in combination:

- said balancing system comprises at the terminals of each accumulator stage (s)

An associated flyback converter comprising a transformer with: a primary winding configured to be connected to the terminals of said associated accumulator stage, and a secondary winding configured to be connected to an auxiliary network whose voltage is less than the voltage of said power battery, and for each accumulator stage (s), a an associated switch connected to a primary winding of said transformer and to the negative terminal of the accumulator stage (s), and said system further comprises:

A device for controlling said flyback converters respectively comprising at least one processing means for: receiving the voltage information of said monitoring device, and when at least one stage has a voltage greater than the voltage of the other accumulator stages; ), controlling the closing of at least one switch of a flyback converter associated with an accumulator stage (s) and the transfer of energy from said stage to the auxiliary network, so as to balance the charge of the accumulator stages ;

said transformer is a planar technology transformer,

said system comprises a plurality of diodes respectively connected in series with said transformers, said diodes being respectively connected by their anode to the secondary winding of a transformer and by their cathode to said auxiliary network;

said control device is configured to control said converters so as to transfer the balancing energy of said stages to said auxiliary network, and said flyback converters have a galvanic isolation,

said control device is configured to control said converters so as to transfer the balancing energy of said stages to an auxiliary battery whose voltage is lower than the voltage of said power battery,

said switches are controlled individually,

said control device is configured to control the closing of the switch associated with an accumulator stage (s) whose voltage is greater than the respective voltages of the other accumulator stages (s), said control device comprises at least one processing means for calculating, for each accumulator stage, a closing time of the associated switch, and controlling the closing of the switches respectively during the associated closing times,

said control device is configured to control said converters so as to supply said auxiliary network with the balancing energy of said power battery,

said control device comprises at least one processing means for determining the power to be delivered respectively by said stages.

The invention also relates to a load balancing method for a power battery comprising at least two accumulator stages connected in series, each accumulator stage comprising at least one accumulator, characterized in that said method comprises the following steps:

the voltage at the terminals of each accumulator stage (s) is measured,

the measured voltages are compared, and

when a measured voltage is higher than the other measured voltages, the closure of at least one switch of a flyback converter whose transformer has at least one primary winding connected to the terminals of an accumulator stage is controlled of said power battery and connected to said switch, and a secondary winding connected to an auxiliary battery whose voltage is lower than the voltage of said power battery, for a transfer of energy of said stage associated with said at least one switch whose closure is controlled to said auxiliary battery, so as to balance the charge of the accumulator stages.

According to a preferred embodiment, such a method is a combined load balancing method for a power battery and an auxiliary battery whose voltage is lower than the voltage of said power battery.

According to one embodiment, said method comprises the following steps: for each accumulator stage (s), a closing time of the associated switch of a flyback converter whose transformer has a primary winding connected to the terminals of the accumulator stage (s) and connected to said switch, and a secondary winding connected to the auxiliary battery, and

the switches are closed respectively during the calculated closing times.

The said load balancing method may include the following preliminary steps:

the voltage at the terminals of each accumulator stage (s) of said power battery is measured,

the measured voltages are compared with a predefined threshold voltage,

- The charge rate of each accumulator stage (s) is determined from the comparison results, making it possible to calculate the closing time.

Alternatively, said load balancing method may include the following preliminary steps:

the measured voltages are compared with each other, and

the most charged accumulator stages are determined so as to calculate longer closing times for the more charged accumulator stages.

According to a particular embodiment, the voltages at the terminals of the accumulator stages are measured at a predefined instant, such as the end of the charging of said power battery.

Other features and advantages of the invention will emerge from the following description given by way of example, without limitation, with reference to the accompanying drawings, in which:

FIG. 1 schematically represents a first embodiment of a balancing system for a power battery, FIGS. 2a and 2b show in greater detail the balancing system of FIG. 1,

FIG. 3 represents a variant of the balancing system for a power battery comprising several battery stage modules in series, FIG. 4 represents a variant of the balancing system with a synchronous rectification,

FIG. 5 schematically illustrates various steps of a method of balancing the load of a power battery according to the first embodiment,

FIG. 6 schematically shows a second embodiment of the balancing system for a power battery for supplying an auxiliary battery,

FIG. 7 represents in more detail the balancing system of FIG. 6,

FIG. 8 schematically illustrates various steps of a combined method of balancing the load of the power battery and the power supply of the auxiliary battery,

FIG. 9 represents in more detail the power battery, an auxiliary battery and the balancing system according to a third embodiment,

FIG. 10 represents a monitoring device and a control device at the terminals of the power battery of FIG. 9,

FIG. 11 diagrammatically shows a fourth embodiment of the balancing system for a power battery for supplying the auxiliary battery, and

- Figure 12 schematically illustrates different steps of a load balancing method of a power battery according to the third embodiment.

In these figures and in the following description, the substantially identical elements are identified by the same reference numbers. FIG. 1 shows schematically:

a battery 1 with a high voltage, for example between 48V and 750V, for example for powering the engine of a hybrid or electric vehicle, and isolated from the chassis of the vehicle,

a balancing system 3 for the power battery 1,

an auxiliary battery 5 with a voltage lower than that of the power battery 1, for example with a voltage of 12V, for supplying, for example, auxiliaries A1, A2 to An in the vehicle, and

- A DC / DC converter 7 between the two batteries 1 and 5 to allow the power supply of the auxiliary battery 5 by the power battery 1 and made with a galvanic isolation to ensure the safety of auxiliaries Al to An.

The power battery 1 is an accumulator battery (s) 9 (see Figures 2a, 2b). This battery 1 may include several accumulators 9 placed in series. This battery 1 may also include one or more additional accumulators placed in parallel accumulators 9 in series so as to form accumulator stages (s) 11. Each stage 11 may therefore comprise an accumulator 9 or more accumulators in parallel.

As can be seen in FIG. 3, the battery 1 may comprise several modules 13 placed in series, each module 13 comprising a predefined number of accumulator stages 11. In the example illustrated, the battery 1 has two modules 13 each having four stages 11 of accumulator (s). With such a series association of modules 13, it is easy to replace a defective module 13.

Of course, other configurations are possible with modules comprising, for example, eight, ten or even twelve stages 11 in series, and each stage 11 comprising two, four or even ten accumulators in parallel as required.

In addition, each module 13 can be connected in parallel with another module 13. 1.1 First embodiment:

We now describe a first embodiment of the balancing system 3. Referring again to Figures 2a, 2b, we see that the balancing system 3 comprises:

- a flyback converter 15 framed by dashes,

a device 17 for monitoring the voltage at the terminals of the stages 11 of accumulator (s) 9, and

a control device 19 for controlling the flyback converter 15 so as to balance the load of the stages 11.

In the case where the battery 1 comprises several modules 13, the balancing system 3 may comprise a single flyback converter 15 for the entire battery 1 or more flyback converters 15 respectively associated with a module 13 as shown in FIG. 3. You can easily replace a faulty flyback converter. In the case of a single flyback converter 15 for all the modules, a balancing between the cells of the same module can be achieved by dissipation in resistors or any other system to limit the cost.

With reference to FIGS. 2a to 3, the flyback converter or converters 15 respectively comprise a transformer 21 surrounded by a dotted line, with:

several primary windings 23 respectively associated with a stage 11 of accumulator (s), and

a secondary winding 25 connected to the auxiliary battery 5.

A flyback converter 15 further comprises on the side of each primary winding 23, a switch 27 made for example by a power transistor for example MOSFET and a protective antiparallel diode. This switch 27 is connected to the negative terminal (-) of the associated stage 11.

The flyback converter 15 also has on the side of the secondary winding 25 a diode 29 and a capacitor 31 in series.

In addition, a blocking diode 33, such as a Schottky diode, may allow to avoid a transfer of energy between the stages 11 of accumulator (s). In addition, the use of a Schottky diode makes it possible to limit the voltage drop at the passage of the diode and also makes it possible to have a lower voltage threshold compared with conventional diodes, for example of the order of 0, 3V.

In order to improve the efficiency and to avoid losses in the Schottky diode 33, it is possible, in a variant, to use a synchronous rectification as shown in FIG. 4 by connecting a diode 35 in place of the Schottky diode 33 and a transistor 37 in parallel.

However, for example in the case of lithium-ion batteries based on iron phosphate (LiFePO4), the voltage differences are very small during charging: the voltages are generally around 3.2V. At the end of the charge, these differences increase to reach 0.5V at the maximum, the maximum charge voltage being 3.7V. The protection diode of the transistor in the switch 27, has a voltage threshold of 0.7V, the difference being 0.5V it prevents any discharge of a more charged stage to a less charged stage. It is then not necessary to put a Schottky diode or to use a synchronous rectification to ensure that a battery stage (s) does not discharge into a less charged accumulator stage (s) and that the energy is well transferred to the auxiliary battery.

At the end of the discharge, we can either limit the minimum voltage to 2.7V to have a difference of 0.5V with the plateau voltage of 3.2V, or decide not to balance at this time. This makes it possible to significantly increase the efficiency and to reduce the costs. This solution is valid for voltage differences between accumulators that do not exceed 0.6 to 0.7V in normal operation.

With regard to the accumulator voltage monitoring device 17, it comprises measuring means 17 'across each stage 11. These measuring means 17' are configured to transmit their measurement results to the control device 19.

The control device 19 comprises meanwhile at least one processing means for:

- receive voltage measurements, - compare the measured voltages, and

- to order the closing of the switches 27.

The higher voltage stage 11 then imposes its voltage on the primary windings 23. The other stages 11 do not discharge due to the presence of the Schottky diode 33. The energy of this stage 11 is therefore transferred via the transformer 21 to the auxiliary battery 5.

As an alternative, the switches 27 may be individually controlled. Thus, the switch 27 associated with the most heavily loaded stage 11 is controlled to be closed.

An exemplary method of balancing the charge of the accumulators 9 of the power battery 1 will now be described with reference to FIGS. 2b and 5.

During a first step El, the voltage is measured at the terminals of the accumulator stages (s). Each stage 11 has a respective voltage V1, V2, V3, V4.

Take the example in which the voltage VI is equal to 3.5V and the voltages V2, V3, V4 to 3.2V, the threshold voltage being for example 3.6V.

The measuring means 17 'across the terminals of the first stage 11 therefore measures a voltage V1 of 3.5V, while the other measurement means 17' respectively measure a voltage V2, V3, V4 of 3.2V.

The control device 19 compares the measured voltages in step E2.

The voltage V 1 across the first stage 11 is greater than the voltages V 2 to

V4 of the other stages 11. Consequently, the control device 19 controls the closing of the switches 27 in the step E3. These switches 27 are controlled in a common way and are thus closed at the same time according to a predefined closing time.

The voltage VI of 3.5V is imposed on the primary windings 23. This voltage

VI being greater than the voltages V2, V3, V4 of the other stages 11, the Schottky diodes for the respective voltage stages V2, V3, V4 are blocked, which prevents the discharge of these stages 11. The primary windings 23 are therefore connected to the most charged stage 11 and this results in an increase in the magnetic flux in the transformer 21. As a variant, only the switch 27 associated with the most voltage-loaded stage 11 is closed. This also results in an increase in the magnetic flux in the transformer 21, the primary winding 23 is connected to this stage 11 more loaded.

In addition, the voltage across the secondary is negative thereby blocking the diode 29.

When the switch or switches 27 open, the diode 29 becomes conductive and also allows the recovery of the voltage which is then filtered by the capacitor 31.

The charge of the accumulators 9 is then balanced by transferring the energy of the most charged stage 11 to the auxiliary battery 5.

This balancing can be done at any time of operation of the vehicle when a consumption is observed on the auxiliary battery 5 or it is possible to charge the auxiliary battery 5. 1.2 Second embodiment:

A second embodiment is illustrated schematically in FIG. 6. This second embodiment differs from the first embodiment in that the balancing system 3 completely replaces the DC / DC converter 7 of the first embodiment allowing to supply the auxiliary battery 5 and providing galvanic isolation for the safety of auxiliaries.

The costs of a DC / DC converter being removed, the balancing system may be larger and the balancing more powerful. In this case, the sizing of the components of the balancing system 3 is adapted for such a transfer of energy from the power battery 1 to the auxiliary battery 5.

According to this second embodiment (FIG. 7), the control device 19 comprises at least one processing means for:

- receive the voltage measurements of the measuring means 17 ',

compare the measured voltages with a predefined threshold voltage,

determining a load rate t _x from the comparison results, calculating a closing time t _f for each switch 27 as a function of the charge rate t _x of the associated stage 11, and

- Individually control the closing of the switches 27 according to the closing times t _f calculated.

An example of a combined charge balancing method of the accumulators 9 of the power battery 1 and the supply of the auxiliary battery 5 will now be described with reference to FIGS. 7 and 8.

During a first step El 00, the voltage is measured at the terminals of the accumulator stages 11. Each stage 11 has a respective voltage V1, V2, V3, V4. This measurement of tension can be done at a predefined moment such as the end of charge or at a moment of rest.

In order to simplify the example, we will consider that the voltage of the accumulator reflects its state of charge. This is not always the case but it makes it easier to illustrate the subject. For LiFeP04 technology accumulators, for example, the state of charge differences can only be estimated from the voltage at the end of charging and / or discharging. Otherwise, the voltage differences between accumulators are often too small to be measured at a reasonable cost.

Take the example in which the voltage VI is equal to 3.3V, the voltages V2, V3 to 3.2V, and the voltage V4 to 3.5V, the threshold voltage being for example 3.6V.

The measuring means 17 'across the terminals of the first stage 11 thus measures a voltage V1 of 3.3V, while the second and third measurement means 17' respectively measure a voltage V2, V3 of 3.2V, and the fourth means of measurement 17 'measures a voltage V4 of 3.5V.

The control device 19 compares, at step E200, each voltage measured at the threshold voltage of 3.6V so as to determine the charge rate t _x of each stage 11. It is therefore determined for the first stage 11 of voltage VI of 3.3V, a charge rate of 91%, for the second and third stages 11 of respective voltages V2, V3 of 3.2V a charge rate of 88%, and for the last stage 11 of voltage V4 of 3.5V a charge rate of 97%>.

In step E300, a closing time t _f of the switches 27 is then calculated. associated with these load rates t _x stages 11. The closing time t _f switches 27 associated with the second and third stages 11 of voltage V2 and V3 will therefore be less than the closing time of the switch 27 associated with the first stage 11 voltage VI, itself less than the closing time of the switch 27 associated with the last voltage stage V4.

According to an alternative embodiment, instead of comparing the measured voltages to a threshold voltage in step E200, they are compared with each other so as to identify the most loaded stages.

In the example given, the voltage V4 of 3.5V is greater than the voltage VI of 3.3V, itself higher than the voltages V2, V3 of 3.2V (V4> V1> V2 = V3). As a result, the voltage stage V4 is more charged than the voltage stage VI which is more charged than the voltage stages V2 and V3.

According to this variant, step E300 then calculates a closing time of the associated switches based on these comparison results so as to more unload the most loaded stages 11. As before, the closing time t _f of the switches 27 associated with the second and third voltage stages V 2 and V 3 will therefore be less than the closing time of the switch 27 associated with the first voltage stage VI, itself less than the closing time. of the switch 27 associated with the last stage 11 of voltage V4.

Finally, in step E400, the switches 27 are closed intermittently according to the closing times calculated so as to discharge the most charged accumulator stages 11 until they reach substantially the same level of charge as the stage 11 of accumulator (s) the least loaded.

In the illustrated example, the stages 11 of respective voltages V4 and V1 are discharged more so that they reach substantially the same charge level of the stages 11 less loaded with voltages V2 and V3.

As previously, this results in an increase of the magnetic flux in the transformer 21, and when the switches 27 open, the diode 29 becomes conductive and also allows the recovery of the voltage which is then filtered by the capacitor 31. The auxiliary battery 5 is thus powered while balancing the charge of the accumulator stages (s) 9 by transferring the energy of the most charged stage 11 to the auxiliary battery 5.

In addition, in the case where the battery 1 comprises several modules 13, the powers provided by the balancing systems associated with these modules 13 add up to supply the auxiliary battery 5.

It is thus understood that the energy transferred from the power battery 1 to the auxiliary battery 5 is used to balance the charge level of the accumulator stages 11 of the power battery 1. In addition, a single electronics can realize the two charge balancing functions of the accumulators 9 of the power battery 1 and the power supply of the auxiliary battery 5.

II.1 Third Embodiment: A third embodiment is now described.

Referring to FIGS. 9 and 10, the balancing system 3 comprises, for each accumulator stage (s) 11, a flyback converter 15 framed in dashed line, and a control device 19 for controlling the flyback converters 15 so as to balance the load of stages 11.

This third embodiment therefore differs from the first embodiment, in that the balancing system 3 has a flyback converter 15 for each accumulator stage (s) 11 and not a converter 15 for a module 13 or for the Thus, the balancing system 3 comprises a plurality of converters 15 connected in parallel between the two batteries 1 and 5.

Each converter 15 is made with a galvanic isolation to ensure the safety of auxiliaries Al to An. A flyback converter 15 comprises a transformer 21, with a primary winding 23 associated with a stage 11 of accumulator (s), and a secondary winding 25 connected to the auxiliary battery 5.

The combination of a transformer 21 with a primary winding 23 and a secondary winding 25 per stage 11 rather than a transformer 21 for several stages 11 makes it possible to choose lower power transformers 21.

In particular, transformers 21 may be provided according to the planar technology on a printed circuit. A planar-type transformer comprises a thin magnetic circuit generally machined ferrite, fixed on the printed circuit in which the turns are made.

A flyback converter 15 further comprises on the side of the primary winding 23, a switch 27 made for example by a power transistor for example MOSFET. This switch 27 is connected to the negative terminal (-) of the associated stage 11.

The flyback converter 15 also has on the side of the secondary winding 25 a diode 29 in series.

Each flyback converter 15 associated with a stage 11 is therefore independent of the other flyback converters 15; which allows simultaneous operation of the converters 15 without interaction of a stage 11 on another stage 11.

II.2 Fourth embodiment:

According to a fourth embodiment illustrated schematically in FIG. 11, the balancing system 3 completely replaces the DC / DC converter 7 of the first variant of the second embodiment making it possible to supply the auxiliary battery 5 and ensuring the Galvanic isolation for the safety of auxiliaries Al to An.

The power delivered by the balancing system 3 is sufficient to supply the auxiliary network called 12V network, or low voltage network, in the embodiment described. In addition, the redundancy of the plurality of flyback converters 15 also makes it possible to dispense with the auxiliary battery 5 to power the 12V network.

The balancing system of the third or fourth embodiment may also include a device 17 for monitoring the voltage across the stages 11 of accumulator (s) 9.

This accumulator voltage monitoring device 17 (FIG. 10) comprises, for example, measurement means at the terminals of each stage 11, configured to transmit their measurement results to the control device 19. The control device 19 can control the switches 27 individually, so that the switch 27 associated with the most loaded stage 11 is controlled to be closed.

The control device 19 may further comprise at least one processing means for receiving the voltage measurements of the monitoring device 17, analyzing the measured voltages, and controlling the closing of one or more switches 27 according to the analysis results. measured voltages.

In order to analyze the measured voltages, the control device 19 may comprise a means for comparing the voltages measured between them and a means for determining the most loaded stages from the comparison results.

According to one variant, the control device 19 may comprise means for calculating a product P for each stage 11 according to the following formula (1):

(1) P = Crefi. (1 - SOCI) (where Crefï = reference capacity of stage i, and SOCi = state of charge of stage i)

Or alternatively, a means for calculating a product F for each stage 11 calculated according to a second formula (2):

(2) P '= Cref. SOCi (where Crefï = reference capacity of a stage i, and SOCi = state of charge of stage i).

The capacity corresponds to the electric charge that can provide the battery and is usually expressed in Ah or mAh. This is an intrinsic characteristic for each accumulator. This value can evolve slowly depending on the temperature, aging, and decreases as the life of the battery. The information on the capacity of each stage 11 may be the result of learning during the different cycles. The reference capacity is usually given by the manufacturer, for example 60Ah.

The control device 19 may further comprise means for determining the stage (s) 11 to be discharged so as to equalize the products P or F for each stage 11.

The control device 19 may comprise according to yet another variant:

a means for comparing the measured voltages with a threshold voltage, a means for determining a charge rate from the comparison results, and

a means for calculating a closing time for each switch 27 as a function of the charge rate of the determined stage 11. The control device 19 may further comprise at least one processing means for determining the power to be delivered by each stage 11 so as to supply the network 12V. II.3 Operation

Charge phase of the power battery

With reference to FIGS. 9 and 10, an example of operation of the balancing system 3 of the third embodiment, in the case of the charging of a power battery 1, is described so as to bring all the stages 11 at a nominal voltage level.

This balancing can be done at the same time as the charge of the battery 1.

This balancing can be done at any time of operation of the vehicle when a consumption is observed on the auxiliary battery 5 or it is possible to charge the auxiliary battery 5.

If the consumption is insufficient on the 12V network, additional consumers can be started to increase the consumption on the 12V, such as heating, air conditioning of the vehicle.

In order to simplify the example, we will consider that the voltage of the accumulator reflects its state of charge. This is not always the case but it makes it easier to illustrate the subject. For LiFeP04 technology accumulators, for example, the state of charge differences can only be estimated from the voltage at the end of charging and / or discharging. Otherwise, the voltage differences between accumulators are often too small to be measured at a reasonable cost. · First variant

During a first step E201 (see FIG. 12), the voltage is measured across the stages 11 of accumulator (s). Each stage 11 has a respective voltage V1, V2, V3, V4.

Take the example in which the voltage VI is equal to 3.3V, the voltages V2, V3 at 3.2V, and the voltage V4 at 3.5V, the threshold voltage being for example 3.6V.

The measurement means at the terminals of the first stage 11 thus measures a voltage V1 of 3.3V, the second and third measurement means respectively a voltage V2, V3 of 3.2V, and the fourth measurement means a voltage V4 of 3, 5V.

This measurement can be done at any time of operation of the vehicle, at regular intervals, or at a predefined time such as the end of charge or a rest period of the vehicle.

The control device 19 can compare in step E202 the measured voltages.

The voltage V4 across the fourth stage 11 is greater than the voltage V1 across the first stage, itself higher than the respective voltages V2 and V3 of the second and third stages 11. The control device 19 can determine from this information, by comparing the voltages measured between them, the 11 most loaded stages.

The control device 19 therefore determines from this information that the most heavily loaded stages 11 are the fourth and the first stage 11, and then controls in step E203 the closing of the associated switches 27.

This results in an increase in the magnetic flux in the transformer 21, the primary winding 23 of which is connected to the fourth stage 11 and in the transformer 21, the primary winding 23 of which is connected to the first stage 11.

The voltage across the secondary 25 is negative thereby blocking the diode 29.

When the switches 27 open, the diode 29 becomes busy.

The energy of the associated stage 11 is therefore transferred via the transformer 21 the auxiliary battery 5.

The charge of the accumulators 9 is then balanced by transferring the energy of the most charged stage 11 to the 12V network.

Second variant

It is also possible to discharge each stage 11 as a function of the state of charge of the stage 11, for example so as to equalize the products P for each stage 11 according to the following formula (1):

(1) P = Crefi. (1 - SOCI)

(where Crefi = reference capacity of a stage i, and SOCi = state of charge of stage i)

The product P increases inversely with the state of charge; more a stage 11 is loaded plus the product P is small. Thus, priority is given to the stages 11 whose products P are the weakest.

It is possible to calculate in step E203 a closing time of the switches 27 as a function of these products P. The smaller the product P, the more the stage is loaded, and the longer the closure time is, so as to discharge in priority the 11 most loaded stages.

And, it controls, the closing of the switches 27 according to the closing times calculated so as to equalize the products P. · Third variant

Alternatively, a charge rate can be determined for each stage and a suitable closing time can be deduced according to the determined charge rate.

The charge rate can be determined with respect to a threshold voltage, for example 3.6V. According to the example given, we thus determine:

for the first stage 11 of voltage VI of 3.3V, a charge rate of 91%,

for the second and third stages 11 of respective voltages V2, V3 of 3.2V a charge rate of 88%, and

- For the last stage 11 of V4 voltage of 3.5V a load rate of 97%.

Step E203 then calculates a closing time of the switches 27 as a function of these charge rates.

The closing time of the switches 27 associated with the second and third stages 11 of voltage V2 and V3 will therefore be less than the closing time of the switch 27 associated with the first voltage stage VI, itself lower than the closing time of the switch 27 associated with the last stage 11 of voltage V4.

Finally, it controls, intermittently closing the switches 27 according to the closing times calculated so as to discharge the most charged accumulator stages (s) 11 until they reach substantially the same level of charge as the stage 11 of accumulator (s) the least loaded.

In the illustrated example, the stages 11 of respective voltages V4 and V1 are discharged so that they reach substantially the same level of charge of the stages

11 less loaded voltages V2 and V3.

As before, this results in an increase of the magnetic flux in the transformer 21, and when the switches 27 open, the diode 29 becomes conducting.

This supplies the 12V network while balancing the load of the stages 11 of accumulator (s) 9 by transferring the balancing energy of the stages 11 to the network

12 V.

Of course, if, as a result of the balancing process, the stages 11 have not all reached the desired charge level, the charging of the stages 11 is continued until a charge level of 100% is reached. Phase of discharge of the battery of power

An example of operation of the balancing system 3 following the discharge of the power battery 1 is now described.

Balancing can be done at the same time as the discharge of the battery 1.

The 11 most loaded stages are used primarily to supply the low voltage network 12V.

To determine the most loaded stages 11, the control device 19 can for example compare the products F for each stage 11 according to the following formula (2):

(2) P '= Cref. SOCi (where Crefî = reference capacity of a stage i, and SOCi = state of charge of stage i)

In this case, the product F increases with the state of charge of each stage 11. Thus, the stages 11 whose products F are highest are firstly discharged.

Of course, alternatively, the most loaded stages 11 are determined by comparing the voltage levels measured similarly to the first variant of the charging phase.

Alternatively, according to another variant, the stages 11 charged are determined by calculating a charge rate by comparison with a threshold voltage, similarly to the third variant of the charging phase.

The control device 19 can further control the power delivered by each stage 11 to power the 12V network.

For example, for the 11 most loaded stages, or whose products F calculated are the highest, these stages 11 will deliver a maximum power Pm, for example 20W.

For the other stages 11, the power Pi to be delivered can be calculated for example according to formula (3): (3) Pi (t) = P12 (t) - Pm * x (with P12 (t) = power consumed on the 12V network at a given moment t, Pm = maximum power delivered by the most loaded stages 11, and x = integer part of the P12 (t) / Pm ratio

It is therefore understood that the energy transferred from the power battery 1 to the auxiliary battery 5 serves to balance the charge level of the battery stages 11 of the power battery 1.

In addition, a single electronic can perform the two functions of load balancing accumulators 9 of the power battery 1 and auxiliary battery power 5.

And, in addition the use of several converters 15 instead of a single converter 15 allows for converters of lower power, compared to a single converter of the prior art, and therefore less expensive.

In addition, this redundancy of the converters 15 facilitates the removal of the auxiliary battery 3 because of the redundancy.

The balancing system 3 can furthermore provide a function of supplying the 12 volts accessory to the vehicle when the converters 15 pass sufficient power.

Claims

Load balancing system for a power battery (1) comprising at least two stages (11) of accumulator (s) connected in series, each stage (11) of accumulator (s) comprising at least one accumulator (9) characterized in that said balancing system comprises at least one flyback converter (15) comprising:

a transformer (21) with:

At least one primary winding (23) configured to be connected to the terminals of a stage (11) of accumulator (s) of said power battery (1), and

A secondary winding (25) configured to be connected to an auxiliary battery (5) whose voltage is lower than the voltage of said power battery (1), and

for each stage (11) of accumulator (s), an associated switch (27) connected to a primary winding (23) of said transformer (21) and to the negative terminal (-) of the stage (11) of accumulator (s), and in that said system further comprises:

a device (17) for monitoring the voltage at the terminals of said accumulator stages (11), and

a control device (19) for said flyback converter (15) comprising at least one processing means for:

• receiving the voltage information of said monitoring device (17), and

• when at least one floor has a voltage greater than voltage of the other accumulator stages (s), control the closing of at least one switch (27) associated with a stage (11) of accumulator (s) and the transfer of energy of said stage (11) to said battery auxiliary, so as to balance the charge of the stages (11) of accumulators.

Balancing system according to claim 1, characterized in that it comprises a predefined number of fiyback converters (15) respectively associated with a predefined number of modules (13) in series with said power battery (1), said modules ( 13) comprising stages (11) of accumulator (s) placed in series.

Balancing system according to claim 1, characterized in that it comprises a common fiyback converter (15) connected to a predefined number of modules (13) in series with said power battery (1), said modules (13) comprising stages (11) of accumulator (s) put in series.

Balancing system according to any one of claims 1 to 3, characterized in that it comprises for each stage (11) of accumulator (s), a blocking diode (33):

connected by its anode to the primary winding (23) of the transformer (21), and

- connected by its cathode to the switch (27) associated.

Balancing system according to claim 4, characterized in that the blocking diode (33) is a Schottky diode.

Balancing system according to any one of claims 1 to 3, characterized in that it comprises for each stage (11) of accumulator (s) a diode (35) and a transistor (37) in parallel, such that the diode (35) is connected by its anode to the primary winding (23) of the transformer (21) and connected by its cathode to the switch (27) associated with the stage (11) accumulator (s). Balancing system according to one of claims 1 to 6, characterized in that the switches (27) of said at least one flyback converter (15) are controlled jointly by said control device (19) so as to be closed at the same time when at least one stage (11) of accumulator (s) has a voltage greater than the respective voltages of the other stages (11) accumulator (s).

Balancing system according to claim 1, characterized in that said balancing system comprises at the terminals of each accumulator stage (s) an associated flyback converter (15) comprising:

a transformer (21) with:

A primary winding (23) configured to be connected to the terminals of said associated accumulator stage (11), and

A secondary winding (25) configured to be connected to an auxiliary network whose voltage is lower than the voltage of said power battery (1), and

a control device (19) for said flyback converters (15) comprising at least one processing means for:

• receiving the voltage information of said monitoring device (17), and when at least one stage has a voltage greater than the voltage of the other accumulator stages, the closing of at least one switch (27) of a flyback converter (15) associated with a stage (11) is required ) accumulator (s) and the energy transfer of said stage (11) to the auxiliary network, so as to balance the charge of the stages (11) of accumulators.

9. Balancing system according to claim 8, characterized in that said transformer (21) is a planar technology transformer.

10. Balancing system according to one of claims 8 or 9, characterized in that it comprises comprises a plurality of diodes (29) respectively connected in series with said transformers (21), said diodes being respectively connected by their anode to the secondary winding (25) of a transformer (21) and by their cathode to said auxiliary network.

11. Balancing system according to any one of claims 1 to 6 or 8 to 10, characterized in that said switches (27) are individually controlled by said control device (19), so as to control the closure switch (27) associated with a stage (11) of accumulator (s) whose voltage is greater than the respective voltages of the other stages (11) accumulator (s). Balancing system according to claim 11, characterized in that said control device (19) comprises at least one processing means for:

calculating for each accumulator stage (11) a closing time (t _f ) of the associated switch (27), and

- to control the closing of the switches (27) respectively during the closing times (t _f ) associated.

Balancing system according to one of Claims 8 to 12, characterized in that the at least one flyback converter (15) is sized for power transfer from the power battery (1) to the auxiliary battery (5) to supply the auxiliary battery (5).

Balance system according to claim 8 taken in combination with any one of claims 9 to 13, characterized in that said control device (19) is configured to control said converters (15) so as to transfer the balancing energy of said stages (11) to said auxiliary network, and in that said flyback converters (15) have a galvanic isolation.

15. Balancing system according to claim 8 taken in combination with any one of claims 9 to 14, characterized in that said control device (19) is configured to control said converters (27) so as to supply said network auxiliary from the balancing energy of said power battery (1).

16. Balancing system according to claim 15, characterized in that said control device (19) comprises at least one processing means for determining the power to be delivered respectively by said stages (11).

17. Balancing system according to any one of the preceding claims, characterized in that it is configured for the load balancing of the stages (11) of accumulator (s) of a power battery (1) Lithium -ion.

18. Balancing system according to any one of the preceding claims, characterized in that it is configured for the load balancing of the stages (11) of accumulator (s) of a power battery (1) supplying the engine of an electric and / or hybrid motor vehicle.

Load balancing method for a power battery (1) comprising at least two stages (11) of accumulator (s) placed in series, each stage (11) of accumulator (s) comprising at least one accumulator ( 9), characterized in that said method comprises the following steps: the voltage (V1, V2, V3, V4) is measured at the terminals of each stage (11) of accumulator (s),

the measured voltages (V1, V2, V3, V4) are compared, and

when a measured voltage is higher than the other measured voltages, the closure of at least one switch (27) of a flyback converter (15) whose transformer (21) has at least one primary winding (23) connected at the terminals of an accumulator stage (11) of said power battery (1) and connected to said switch (27), and a secondary winding (25) connected to an auxiliary battery (5) whose voltage is less than the voltage of said power battery (1), for a power transfer of said stage (11) associated with said at least one switch (27) whose closure is controlled to said auxiliary battery, so as to balance the load of the stages (11) of accumulators.

Balancing method according to claim 19, characterized in that said method comprises the following steps:

for each stage (11) of accumulator (s), a closing time (t _f ) of the associated switch (27) of a flyback converter (15) whose transformer (21) has a primary winding (23) is calculated ) connected to the terminals of the accumulator stage (11) and connected to said switch (27), and a secondary winding (25) connected to the auxiliary battery (5), and

- The closing of the switches (27) is controlled respectively during the closing times (t _f ) calculated.

21. The method of claim 20, characterized in that it comprises the following preliminary steps:

the voltage (V1, V2, V3, V4) is measured at the terminals of each stage (11) accumulator (s) of said power battery (1),

the measured voltages (V1, V2, V3, V4) are compared with a predefined threshold voltage,

- The charge rate (t _x ) of each accumulator stage (s) (11) is determined from the comparison results, making it possible to calculate the closing time.

22. The method of claim 21, characterized in that it comprises the following steps:

the voltage (V1, V2, V3, V4) is measured at the terminals of each stage (11) of accumulator (s) of said power battery (1),

the measured voltages (V1, V2, V3, V4) are compared with each other, and

the most charged accumulator stages (11) are determined so as to calculate longer closing times for the more charged accumulator stages (11).

23. Method according to one of claims 21 or 22, characterized in that the voltages (V1, V2, V3, V4) at the terminals of the accumulator stages (11) are measured at a predefined instant, such as that the end of the charge of said power battery (1).