WO1999025053A1

WO1999025053A1 - Method and system for charging a battery with storage cell modules

Info

Publication number: WO1999025053A1
Application number: PCT/FR1997/002004
Authority: WO
Inventors: Wolfgang Bogel; Jean-Pierre Buchel; Christian Hiron; Serge Torelli
Original assignee: Renault
Priority date: 1996-09-26
Filing date: 1997-11-07
Publication date: 1999-05-20
Also published as: FR2753838B1; FR2753838A1

Abstract

The invention concerns a method and a system for charging a battery with storage cell modules (M1-M20). The invention is characterised in that it consists in defining in the battery groups (G1-G5) of storage cell modules, and in breaking down at least one charging phase of the battery into a plurality of successive and recurrent microcycles for charging each group of the storage cell modules. The invention enables to charge the battery with a strong current while maintaining a charging power compatible with the domestic electric system. It is particularly applicable for producing an on-board charging system in electric motor vehicles.

Description

METHOD AND SYSTEM FOR CHARGING A MODULE BATTERY

ACCUMULATORS

The present invention relates to a method and a system for charging a battery of accumulator modules.

The present invention relates in particular but not exclusively to the field of motor vehicles with electric traction motor.

FIG. 1 is the electrical diagram of a battery of accumulator modules 1 of an electric vehicle and its charging system 2. In order to present a high energy capacity necessary for the traction of the vehicle, the battery comprises a large number of accumulator modules , here twenty modules Ml to M20 arranged in series. The modules are for example with a nominal voltage of 12 V and a capacity of 60 Ah (Ampere Hours), the battery thus delivering on its terminals B ⁺ and B ^" a nominal voltage Unom of 240 V. The charging system 2 of the battery, generally on board the vehicle, is supplied by an alternating voltage source Va and essentially comprises a charger 3 controlled by a programmed sequencer 4. Sensors 5, 6, 7 are provided for detecting respectively the charging current I , the voltage U and the temperature T of the battery, the outputs of the sensors being sent to inputs of the sequencer 4. In practice, the efficiency of the charging system 2 lies in the programming of the sequencer 4. Each type of battery requires effect a specific load profile which must be strictly observed in order not to damage the battery and guarantee its lifespan. The charge profile of a battery is thus conventionally broken down into a succession of phases at constant current, voltage, or power. In particular, for a certain battery technology, it is conventional to provide an initial charging phase carried out at constant current or power. Such an initial charging phase can extend in this case until the moment when the voltage U of the battery, at a low value at the start of charging, reaches a switching value Uc generally: greater than the nominal voltage Unom .

Work carried out by the applicant has shown that accelerating the initial charging phase, that is to say carrying out this phase with a charging current at least twice greater than that delivered by a conventional on-board charger, improves the charging efficiency and the lifespan of a battery as well as the thermal behavior and consequently the availability of the vehicle (the charging efficiency being the ratio between the quantity of actual electricity accumulated by the battery and the quantity of electricity Q supplied to it).

However, a high charging power is required for this. For example, the supply of a charging current of 40 A to the battery of nominal voltage of 240 V previously described represents a considerable charging power of 12000 W (the switching voltage Uc being greater than the nominal voltage Unom). While it is technically possible to deliver such power from a high-power charger with a fixed station, it is not the same with an on-board charger, which must be light, compact and cost returns reduced. In addition, it is desirable that an on-board charger can be powered from an outlet on the domestic electrical network of the most widespread, for example a 220V / 16A socket. However, such an electrical outlet cannot deliver a power greater than 3500 W.

Thus, conventional charging methods and systems do not allow a large capacity storage battery to be charged with a high current from a household electrical outlet.

The present invention aims, in particular, to overcome this drawback. In particular, an objective of the present invention is to charge a battery of accumulator modules with a high current while maintaining a reasonable charging power and compatible with a household electrical outlet. Another objective of the present invention is to provide a medium power charging system capable of delivering a high current while having a cost price and a space comparable to those of a conventional on-board charging system. These and other objectives are achieved by a method for charging a battery of accumulator modules, comprising the steps of defining groups of accumulator modules in the battery, and breaking down at least one phase of a charge cycle. of the battery into a plurality of successive and recurrent partial charge microcycles of each of the groups of accumulator modules.

Preferably, groups of accumulator modules of the same voltage are defined. As the accumulator modules constituting a battery are generally chosen to have the same voltage, this means that the accumulator groups comprise the same number of accumulator modules.

According to one embodiment, a first charging phase is provided at constant power or current, decomposed into a plurality of partial charge microcycles, and a second charge phase at constant voltage.

Advantageously, the first charging phase is carried out with a high current, in accordance with one of the objectives of the present invention.

According to one embodiment, all or part of the second charging phase is broken down into a plurality of successive and recurrent microcycles of partial charge of each of the groups of accumulator modules. According to one embodiment, a third low-current charging phase is also provided, carried out collectively on all of the modules of the battery. The present invention also relates to a system for charging a battery of accumulator modules, comprising a battery charger, switch means arranged to delimit in the battery groups of accumulator modules which can be individually connected to the charger, and means for controlling the switch means, arranged for, during at least one phase of charging the battery, successively and repeatedly connecting each of the accumulator groups to the battery charger.

According to one embodiment, the system can further comprise a second low-power charger connected to the terminals of the battery.

The present invention also relates to an electric motor vehicle comprising a battery of accumulator modules and a charging system according to the invention.

These and other objectives, features and advantages of the present invention will be explained in more detail in the following description of the charging method according to the invention and various examples of realization of charging systems according to the invention, in relation to the attached figures among which: FIG. 1 previously described represents a series type storage battery and a conventional charging system for this battery, FIG. 2 represents a charging system charge according to the invention applied to the battery of FIG. 1,

FIGS. 3A to 3G are curves of various electrical signals illustrating the operation of the charging system of FIG. 2, FIG. 4 represents a charging system according to the invention applied to a battery of the series-parallel type,

- Figure 5 is a current and voltage curve illustrating an example of load profile according to

The invention,

- Figure 6 shows an alternative embodiment of the charging system of Figure 2, allowing in particular the implementation of the charging profile of Figure 5, and - Figure 7 shows an alternative embodiment of the charging system of Figure 4, allowing in particular the implementation of the load profile of FIG. 5.

FIG. 2 represents a charging system 10 according to the invention applied to the battery already described in the preamble, comprising twenty accumulator modules Ml to M20 in series. The charging system 10 conventionally comprises a charger 11 which can be connected to a household electrical outlet of the 220V / 16A or 220 V / 32A type, a programmed sequencer 12, and sensors 13, 14, 15 for detecting, respectively, the current I delivered by the charger 11, the charging voltage V and the temperature T of the battery.

According to the invention, the charging system 10 further comprises eight switches SI to S8 controlled by signals C1 to C8 delivered by the sequencer 12. The switches SI to S8 are arranged so as to delimit in the battery groups of accumulator modules which can be individually connected to the charger 11. Here, the eight switches show four groups Gl, G2, G3, G4 of five modules each, represented by lines dashed in FIG. 2. The group Gl comprises the modules M1 to M5 and its positive and negative terminals can be connected to the positive and negative terminals of the charger 11 by means of the switches SI and S2 when these switches are closed and the other switches S3 to S8 open. In the same way, the group G2 includes the modules M6 to M10 and can be connected to the charger 11 thanks to the switches S3 and S4. Group G3 includes modules Mil to M15 and can be connected to charger 11 using switches S5 and S6. Finally, group G4 includes modules M16 to M20 and can be connected to charger 11 by means of switches S7 and S8.

According to the method of the invention, at least one phase of a cycle of charging the battery is broken down into a plurality of microcycles mcl, mc2, mc3, mc4 of partial charge of each of the groups Gl to G4, the microcycles succeeding each other and repeating until the considered charging phase is completed. As illustrated in FIG. 3A, the sequencing over time of the microcycles can for example be as follows: mcl, mc2, mc3, mc, mcl, mc2, mc3, mc4, etc. The duration Tm of the microcycles is preferably chosen relatively short compared to the total duration of the charging phase, for example of the order of ten seconds. The time interval separating the microcycles is not shown to scale in FIG. 3A and can be reduced to the minimum necessary for the switching of the switches SI to S8.

To fix the ideas, FIG. 3B represents the distribution of the charging voltage V delivered by the charger 1 on the groups G1 to G4 during the microcycles mcl to mc4 (in a simplifying approximation, it is assumed that the charging voltage V is constant and identical for all the groups of modules). FIG. 3C represents the voltage V _sa at the terminals of the switch S8, that is to say the difference in voltage appearing between the negative terminal of the battery and the negative terminal of the charger 11. FIG. 3D represents the signals Cl , C2, Figure 3E the signals C3, C4, Figure 3F the signals C5, C6, and Figure 3G the signals C7, C8. A switch being by convention closed when its control signal is at 1, it can be seen that the switches SI, S2 are closed during the microcycles mcl, the switches S3, S4 closed during the microcycles mc2, etc.

A first advantage of the method of the invention is that the charge power applied to the battery is shared by a limited number of modules, so that it becomes possible, for a given charge power, to distribute a charge current more Student. For example, when the modules Ml to M20 are 12V / 60Ah each, the groups Gl to G4 according to the invention have a nominal voltage of 60 V and can be charged with a current close to 40 A under a load power of 3000 W compatible with the domestic electrical network. According to the prior art, the supply of such a current to a battery with a nominal voltage of 240 V would require a charging power of the order of 12000 W, as indicated in the preamble, and a charging power of 3000 W allowed to distribute only a current close to 10 A. In summary, if the number n represents the number of groups of modules (n being here equal to 4), the intensity that can be delivered using the process of the invention is equal to n times the intensity that can be delivered by a conventional charging process. In addition, the Applicant has found that the charging method according to the invention makes it possible to extend the life of a battery. This advantage, independent of that resulting from the application of a high charging current, comes from the fact that each module, after having undergone a charging microcycle, benefits from a rest period Tr of a duration equal to

Tr = (n-l) Tm

Such a rest period allows a "relaxation" of the electrolyte of the accumulators of each module and the elimination of electrochemical phenomena harmful to the accumulators appearing during uninterrupted charge cycles.

Finally, it can be noted that the total charging time of a battery by the method of the invention is not longer than with a conventional charging method, the increase in the charging current compensating for the division of time load of each group in microcycles followed by the rest period Tr.

Given these various advantages, it will be clear to those skilled in the art that the scope of the present invention is broad and exceeds the objective initially described in the preamble. In particular, a charging phase carried out with a current of medium intensity but broken down into partial charge microcycles according to the method of the invention better preserves a battery than an uninterrupted charging phase according to the prior art, carried out with the same current . The fact of carrying out such a charging phase with a high current, in accordance with another aspect of the present invention, makes it possible to further extend the life of the battery. Of course, the application of the present invention is not only reserved for the series type battery previously described. By way of example, FIG. 4 represents a charging system 20 according to the invention provided for a series-parallel type battery. In this battery, the modules Ml to M20 are arranged in two parallel branches, the first branch comprising the modules Ml to M10 in series and the second branch the modules Mil to M20 in series. We find in the charging system 20 the groups Gl to G4 defined by the switches SI, S2, S3, S5, S6, S7, the switches S4 and S8 being replaced by a common switch S48 making it possible to connect the negative terminals of the groups G2 and G4 to the negative terminal of the charger 11. An electromechanical switch S9 is also arranged between the branch M1-M10 and the branch M11-M20. This switch is kept open during charging periods to prevent a possible voltage imbalance between the two branches from leading to the appearance of a current which would tend to restore this balance.

It will be noted that the charging systems which have just been described make it possible to carry out charge phases broken down into microcycles as well as overall charge phases of the battery. To carry out overall charge phases, it is necessary to close the switches SI and S8 in the case of the diagram in FIG. 1 or to close the switches SI, S5, S9 and S48 in the case of the diagram in FIG. 4. The figure 5 is a diagram as a function of the time of the charging current I and of the voltage U of a battery, illustrating an example of a complete charging cycle according to the invention. The charging cycle firstly comprises a high power PI phase carried out in this example with a constant current according to the method of the invention, for example a current of 50 A if the battery includes modules of 12V / 60Ah. The phase PI is stopped at an instant tl, for example when the voltage U of the battery reaches the switching value Uc mentioned in the preamble and generally greater than its nominal voltage Unom. It is followed by a phase PU at constant voltage where a charge voltage equal to Uc is imposed on the battery and during which the charge current I decreases. Instead of continuing the phase PU until the charging current I is canceled, the charging cycle can advantageously be completed from an instant t2, as illustrated in FIG. 5, by a third low-power phase Pi , or overload phase, carried out with a constant charging current of low value ic causing the voltage U of the battery to increase beyond the switching value Uc.

The practical implementation of such a Pl-PU-Pi charge cycle by means of the charge systems shown in FIGS. 2 and 4 implies the provision of a charger 11 capable of operating in very different power ranges. However, in practice, it turns out that such a charger is complex and expensive to produce. To overcome this drawback, the present invention proposes to carry out the charging cycle Pl-PU-Pi by means of two separate chargers, one medium power charger for the PI phase and the other of low power for the Pi phase.

Thus, FIGS. 6 and 7 respectively represent alternative embodiments 10 ′ and 20 ′ of the charging systems shown in FIGS. 2 and 4, in which the charger 11 is relayed at least during the phase Pi by a low power charger 16. The charger 11 is for example a 3000 W charger sized to deliver a charging current of 40 A at a voltage up to 72 V, and the charger II

16 a 400 W charger sized to deliver an ic current of 1 A at an increasing voltage which can reach a limit value of the order of 320 V. The charger 16 is directly connected to the terminals B ⁺ , B ^~ of the battery and is controlled, like the charger 11, by the sequencer 12. In addition to the parameters I, V, T previously described, the sequencer 12 can control, using sensors 17 and 18, the voltage U of the battery and the current I 'delivered by the generator of low power 16. Furthermore, in FIG. 6, the switches S2 to S6 of FIG. 2 take the form of thyristors T2 to T6 triggered by the signals C2 to C6 and the switches SI and S8 are replaced for the sake of economy by diodes Dl and D8. In FIG. 7, the switches S2, S3 and S6, S7 of FIG. 4 also take the form of thyristors T2, T3 and T6, T7 and the switches SI, S5 and S48 are replaced by diodes D1, D5 and D48.

As far as the PU phase is concerned, two operating variants can be envisaged. The first variant consists in carrying out the PU phase entirely by means of the power charger 11. The second variant consists in carrying out a first part of the PU phase by means of the charger 11, as long as the power consumed by the battery is high, then toggling on the low power charger 16 when the power demanded by the battery becomes compatible with this charger. Part or all of the PU phase produced by the charger 11 can optionally be broken down into microcycles according to the invention, initially provided for the PI phase because of the high current it requires.

Those skilled in the art will note that the method of the invention can be advantageously applied to any type of battery (lead, nickel / cadmium, nickel / metal hydrides, sodium / nickel chloride, lithium, ...) whatever the arrangement of the modules (series, series-parallel, parallel) and their nominal voltage. Thus, in the above, we defined in a battery of twenty accumulator modules four groups of five modules each. We could have defined five groups of four modules (by providing two additional switches), or ten groups of two modules, etc. Among all the possible arrangements, one will preferably define arrangements of modules showing groups of the same voltage, that is to say comprising the same number of modules.

For the sake of simplicity, we have not described in the foregoing various characteristics of implementation of the present invention which are within the reach of ordinary skill in the art. In particular, the initial PI charging phase ends for a group of modules when the criterion for stopping this phase is reached. This stopping criterion can be chosen collective (for example the fact that the battery voltage U reaches the switching value Uc) or individual (for example the fact that the voltage of each group of modules reaches its own switching value Ugc) . If a group of modules reaches the individual stop criterion before the end of the charge microcycle which is applied to it, two solutions can be provided: one where the sequencer 12 switches the charge current to the next group of modules in the 'cyclic order chosen, the other where the sequencer switches the charging current to the next group of modules which has not yet reached the stopping criterion during the previous microcycles. The second solution requires that the charging system be more "intelligent" and memorize the state of charge of each group at the end of each microcycle. A microprocessor sequencer 12 can then be provided. Those skilled in the art will also note that in practice, the effective charging time of each group of modules during the PI phase can vary significantly. Such a dispersion of the charging energy efficiency can have various causes and be taken into account when programming the sequencer 12 by providing a charging subroutine intended for lagging groups and ensuring corrective action. Such a corrective action may for example consist in carrying out a homogenization preload for the groups of modules which have shown during previous cycles a depth of discharge higher than the average, in order to bring them back to the charge level of the other groups. Those skilled in the art may also consider, as another corrective action, charging each of the groups of modules with personalized microcycles having for example different durations or different charge currents I.

As regards the sequence of the phases PI and PU in the case where the criterion for stopping the phase PI is applied individually, those skilled in the art can program the sequencer 12 according to two different methods. The first consists in waiting until all the groups of modules have reached the criterion for stopping the PI phase before engaging the PU phase. The second consists in applying the PI-PU load profile to each group without taking the other groups into account, one group being able to be in the PU phase while the other is still in the PI phase. The present invention is thus susceptible of numerous variants and embodiments within the reach of those skilled in the art. Of course, the present invention is also capable of applying to any accumulator system other than a vehicle battery with an electric traction motor.

Claims

1. Method for charging a battery (1) of accumulator modules (M1-M20), comprising the operations consisting in: defining groups of accumulator modules (G1-G4) in the battery,

- decompose at least one phase (PI) of a charge cycle (Pl-PU-pi) of the battery into a plurality of successive and recurrent microcycles (mcl-mc4) of partial charge of each of the groups of accumulator modules.

2. Method according to claim 1, in which groups (G1-G4) of accumulator modules of the same voltage are defined.

3. Method according to one of claims 1 and 2, successively comprising a first charging phase (PI) at constant power or current, broken down into a plurality of microcycles (mcl-mc4) partial charge, and a second charging phase (PU) at constant voltage (Unom).

4. The method of claim 3, wherein the first charging phase (PI) is carried out with a high current.

5. Method according to one of claims 3 and 4, wherein all or part of the second charging phase

(PU) is broken down into a plurality of successive and recurrent partial charge microcycles of each of the groups of accumulator modules.

6. Method according to one of claims 3 to 5, comprising a third charging phase (Pi) at low current carried out collectively on all of the modules (M1-M20) of the battery.

7. Charging system (10, 10 ', 20, 20') for a battery (1) of accumulator modules, comprising a 15

battery charger (11), characterized in that it further comprises:

switch means (S1-S9, T2-T6, Dl, D8, D48) arranged to delimit in the battery groups of accumulator modules (G1-G4) which can be individually connected to the charger (11), and

- control means (12) of the switch means, arranged for, during at least one charging phase (PI, PU) of the battery, successively and repeatedly connecting each of the accumulator groups to the battery charger (11 ).

8. Charging system (10 ', 20') according to claim 7, further comprising a second charger (16) of low power connected to the terminals (B ⁺ , B ^~ ) of the battery.

9. Charging system according to one of claims 7 and 8, wherein the switch means comprise diodes (Dl, D5, D8, D48).

10. Electric motor vehicle comprising a battery of accumulator modules and a charging system according to one of claims 7 to 9.