FR2778281A1 - Protection of battery modules without increasing internal resistance, particularly applicable to Li-ion elements used in electric vehicle secondary generation - Google Patents

Abstract

A battery module consists of six electrochemical elements (11, ..16 ) each having a pressure sensitive sensor which closes a corresponding contact (51,...56) when the element pressure exceeds a threshold. A relay coil (7) is then energized and the relay contact (9) short circuits the battery module and the module protection (3) which may consist of a fuse or alternatively a transistor or thirster

Description

I

PROTECTION FOR BATTERY MODULE

  The subject of the present invention is a battery module, comprising at least one electrochemical cell, and at least one malfunction sensor for one or more of the electrochemical cells. The invention relates to the protection of battery cells against malfunctions, such as overpressures for sealed cells,

  excessive temperatures, overvoltages, or undervoltage, short-

circuits, and others.

  US-A-5 488 285 describes a circuit making it possible to cut the automatic charge of an alkaline battery formed by a set of sealed elements connected in series. At least one element is provided with a pressure detector, which controls the opening of a switch when the pressure in the element exceeds a predetermined pressure. The opening of the switch controls a relay, which itself controls another relay located on the battery usage circuit. This device has the following drawback: the relay

  opening of the operating circuit is arranged on the operating circuit itself -

  even and operates under the total power and total intensity of the circuit. This can cause electric arc problems when the number of elements is large and the operating voltage becomes large. In addition, the relay contacts operate continuously on the operating circuit, which can damage them. Finally, the relay is permanently placed on the

  operating circuit, which can induce additional resistance.

  US-A-3,622,397 describes a Ni-Cd battery formed by a set of

  sealed cells mounted in series. Each cell is provided with a cutter

  mechanical circuit, formed by a wall deformable under the effect of pressure; when the circuit breaker of one of the cells is actuated, this cell is charged by a leakage load current through a resistor. A bimetallic strip acting as a temperature sensitive circuit breaker is placed between neighboring cells; when the temperature increases, the bimetallic strip opens the charging circuit, and the cells are charged by a weaker current, through a resistor mounted in parallel with the circuit breaker. This device presents the

  same drawbacks as the above.

  There are also pressure circuit breakers for small capacity elements, for example on elements marketed by Sony under the reference VL18650. These elements include a circuit breaker on the line of use with a pressure sensor in the element; this solution presents

  again the disadvantage of resistance on the line of use.

  The invention proposes a solution to the problem of protecting a battery module, using a circuit breaker arranged in or on the module, and in particular proposes a solution to the problem of protection.

  of a module, without increasing its internal resistance.

  More specifically, the invention proposes a battery module, comprising at least one electrochemical element, at least one sensor, and means for electrically isolating the electrochemical elements controlled by the sensor, the module remaining conductive when the sensor controls the

so-called means of insulation.

  Advantageously, the module remains conductive after the sensor has

  ordered the said means of insulation.

  In one embodiment, said isolation means comprise a fuse mounted in series with the electrochemical elements, and a relay controlled by said sensor and the power circuit of which closes the circuit.

  series of elements and fuse.

  Advantageously, the sensors include a pressure switch, preferably a pressure switch for each element. The sensor switches are preferably mounted in parallel, and the assembly is mounted in

series with the relay coil.

  In one embodiment, the assembly mounted in series with the coil

  of said relay is mounted across said elements.

  In one embodiment, the switches of the sensors are mounted in series, closed at rest and open in the control position, and the assembly controls the coil of said relay by means of a

transistor.

  In another embodiment, said sensors are electrically powered sensors. They can be chosen from temperature sensors, pressure sensors, sensors detecting overvoltages,

  undervoltage or short circuits.

  Advantageously, the sensor or sensors include a timing circuit. Preferably, the sensor (s) control the relay by

  through a seesaw. The relay can be a bi-stable relay.

  In one embodiment, the isolation means comprise a fuse mounted in series with the electrochemical elements, and an electronic switch controlled by said sensor which closes the series mounting of the elements and the fuse. The switch can be chosen from MOS, transistor,

thyristor, IGBT.

  The invention also provides a method for protecting against a malfunction of a battery module comprising at least one electrochemical element mounted in series with a fuse, at least one sensor and a switch controlled by said sensor, the method comprising controlling the switch by the sensor when the sensor detects a malfunction, the switch then closing the series mounting of the elements

and the fuse.

  Advantageously, the switch remains closed after being controlled by a sensor. Preferably, the switch is controlled by the sensor if the

  malfunction persists after a timeout period.

  The invention provides protection for the contacts of the relay, which is only subjected to the voltage of a module, regardless of the number of modules mounted in battery; it prevents the relay contacts from working permanently on the power line. It limits the presence of organs on the power line, and therefore does not disturb the operation of the battery,

  and does not significantly increase the resistance of an element.

  Other characteristics and advantages of the invention will become apparent on

  reading the following description of embodiments of the invention,

  given by way of example and with reference to the appended drawings which show: - Figure 1 a schematic representation of a module according to an embodiment of the invention; - Figure 2 a schematic representation of a module according to another mode

for carrying out the invention.

  Figure 1 shows a schematic representation of a module according to the invention. Such a module is intended to be assembled in series with other modules on a power line, to form a battery. In the embodiment of FIG. 1, the invention provides protection against overpressure in the various elements of the module. In this embodiment, as in that of FIG. 2, the electrochemical elements are protected by isolating them in the event of malfunctions; however, the module remains electrically conductive, before, during or after the

  security system operation.

  The module of FIG. 1 is formed by several electrochemical elements - six elements 11 to 16 in the case of the figure - mounted in series on a power line 2. A fuse 3 is mounted in series with the elements, on the line of power 2. In at least one element, a pressure switch is provided, formed by a pressure detector not shown, which controls the closing of a switch; in the embodiment of Figure 1, each element is provided with a pressure switch; the switches 51 to 56 of each of the pressure switches are mounted in parallel; the switches 51 to 56 are connected in series with the coil 7 of a relay 8; the series mounting of the switches 51 to 56 and of the relay coil is mounted in parallel at the terminals of the elements 1 1 to 16. The terminals of the power circuit 9 of the relay are connected to the terminals of the serial mounting of the elements and the fuse, the relay coil controls the short-circuiting of the elements 1 1 to

16 and fuse 3.

  The operation of the module in FIG. 1 is as follows. In the position shown in the figure, which is the normal load position, the pressure in each element is lower than the set pressure of the pressure switch; each pressure switch is therefore open, and the module elements are loaded by the power line. In this state, the relay power circuit contacts are not placed on the power line, and therefore

don't work all the time.

  When the pressure in at least one element, for example element 12, exceeds the set pressure, the switch 52 of the corresponding pressure switch closes; in this way, the coil 7 of the relay 8 is supplied, and

  controls the short-circuiting of the elements 1 1 to 16 through the fuse 3.

  The fuse blows, and isolates the elements 1 1 to 16, which avoids any overpressure.

  We are then in degraded mode, and the current flowing in the other modules constituting the battery is maintained through the relay, while the

  electrochemical elements of the defective module are isolated from the battery.

  The invention provides protection of the elements, without increasing the internal resistance of the module in normal operation; in fact, only the fuse, in normal operation, is added to the power line, and it has a low resistance compared to the resistance of the elements. The relay coil, in the assembly, is supplied by the elements themselves, so that the proposed circuit is autonomous, and does not require an external voltage source; to protect the relay against the current flowing in degraded mode in the power line, which may be too large, a protection resistor can be provided, in series with the relay. Again, in normal operation, the relay coil is not energized, and this

  resistance is crossed by no current.

  In addition, the relay, when it closes, is only subjected to the voltage of the elements which it insulates, and not to the voltage of the entire battery; the invention thus provides protection for the relay, whatever the number of modules forming the battery, and therefore whatever the voltage of the latter. Similarly, the fuse, when opened, is only subjected to the voltage of the module elements; in either case, the phenomena of electric arcs are avoided. The system can easily be adapted by choosing the fuse. In a preferred embodiment, the relay 8 is a two-stage relay intended to remain closed, even if the pressure in the element or elements decreases and drops below the set value. In this case, the module remains conductive through the power circuit of the relay; the relay can then be

  reset by opening the power circuit when replacing the fuse.

  In this embodiment, the module of the invention is particularly suitable for use for batteries of electric vehicles. It makes it possible, when charging the vehicle battery while driving, to avoid the problems linked to an overpressure in an element of a module, by ensuring that the other modules remain charged. This ensures that the vehicle can

  continue to operate in degraded mode, until the fuse is replaced.

  In another embodiment, the power circuit of the relay can open when the pressure value decreases, following the isolation of the module. This application ensures the complete opening of the circuit when the

  pressure drops below the set value.

  In any case, the embodiment of FIG. 1 ensures a passive and self-sufficient system, which operates without an external power source, and which

  can simply be mounted in the module housing.

  Figure 2 shows another embodiment of the invention. The embodiment of Figure 2 is intended to provide protection against malfunctions of one or more of the module elements, using sensors requiring a clean power supply. To this end, the module of Figure 2 is associated with an external power supply, for example an external battery 1 1; such a battery can in particular be common to several modules. This battery supplies one or more sensors 12, which control the coil 14 of a relay 13. As in the embodiment of FIG. 1, the power circuit 15 of the relay closes the serial circuit of the fuse and of the electrochemical elements of the module . In this embodiment, insofar as there is in any event an external supply, it is also simple to supply the relay with this supply; a solution of the type of that of FIG. 1 nevertheless remains possible. The fact of ensuring the supply of the relay by the elements of the module has the advantage that the electrochemical elements of the module, after opening of the fuse, self-discharge slowly from the supply of the coil; this ensures slow discharge of the elements, which do not remain

  overloaded, and are no longer dangerous in the long term.

  In the embodiment of FIG. 2, sensors of all kinds can be used. For example, it is possible to provide temperature sensors, so as to detect if the temperature of one or more elements of the module exceeds a set value. For this, it is advantageous to use as temperature sensors resistors with positive temperature coefficient (PTC) connected in series, as explained for example in

US-A-4,967,176.

  Sensors can be used to measure the voltage, and thus detect overvoltage or undervoltage at the terminals of the module or its elements. It is enough for that to use operational amplifiers

  mounted in comparators. This solution also makes it possible to detect short-

  circuits in the module; indeed, such short circuits would cause undervoltage. You can also use one or more sensors dedicated to

short circuit detection.

  In the embodiment of FIG. 2, provision can be made for the sensors to control the relay via a rocker; this solution ensures that the relay remains energized, and its power circuit closed, even when the sensors no longer detect the malfunction; this provides a solution comparable to that described with reference to Figure 1, where the module remains conductive after the fuse blows, regardless of the results of the sensor measurements. If a bi-stable relay is used, such

tipping is not essential.

  We can combine the embodiments of Figures 1 and 2. In this case, we can for example control the relay by pressure switches mounted in parallel on the one hand, and on the other hand by the sensors of Figure 2. We can also use electrically controlled pressure detectors, for example strain gauge pressure sensors, the output signal of which is used as in the embodiment of FIG. 2. It appears in any event that one can multiply the number of sensors; and mount these in parallel with the relay terminals to detect the occurrence of a malfunction. It would also be possible to mount sensors in series at the relay terminals, insofar as one wishes not to command closing

  of the relay only in the event of multiple malfunctions.

  In one embodiment as in the other, it is possible to provide time delay means, for example a time delay circuit. Such a circuit makes it possible to command the closing of the relay only if the malfunction (s) detected by the sensor (s) persist for one

  certain duration. This avoids nuisance trips.

  It is possible to provide that the sensors - in particular the pressure switches -

  are conductors in normal operation of the elements, and open in the event of a malfunction; in this case, the sensors are connected in series, and control the relay via a transistor. This solution has the advantage of greater reliability: if one of the sensors fails, the series circuit of the sensors opens and controls the insulation of the

elements.

  The invention applies in particular to electric vehicles, and very particularly to Li-ion elements, for secondary generators intended for such vehicles. Preferably, an electrochemical Li-ion couple is used, and planar or spiral electrodes, i. e. prismatic or cylindrical elements. The invention applies for example to the

  protection of a module formed by six cylindrical elements.

  In the two embodiments described, and in particular in the application to electric vehicles, it is advantageous for the module to remain conductive after the sensor has commanded the isolation means; this

  can be ensured, in the embodiment of FIG. 1, by a two-way relay

  stable; one can also provide that the sensors, once closed, remain closed.

  In the embodiment of FIG. 2, this can be ensured by a rocker, or by an appropriate choice of the components. In all these examples, there is a memory function in the command chain; this function ensures that the module remains conductive, as soon as the sensors have

  detected a malfunction, and regardless of the subsequent condition of the elements.

  Of course, the present invention is not limited to the examples and embodiments described and shown, but it is susceptible of numerous variants accessible to those skilled in the art. In the assembly of figure 1, the switches of the pressure switches and the coil of the relay could be assembled at the terminals of the series assembly of the elements and the fuse, and not

not across the elements.

  We could not use a single relay, but two or more relays connected in parallel, depending on the current intended to pass through the module; these parallel relays functionally constitute a single relay. One could also use in place of the relay or relays an electronic switch, such as MOS, transistor, thyristor, IGBT or other; this solution has the advantage of

  compactness, and avoids any mechanical movement.

Claims (14)

  1.- A battery module, comprising at least one electrochemical element (11-16), at least one sensor (51-56, 12), and means (8, 9, 13, 15) for electrical insulation of the elements electrochemical controlled by the sensor, the module remaining conductive when the sensor controls the said means of insulation.   2.- The module according to claim 1, characterized in that the module remains conductive after the sensor has ordered the said insulation means 3.- The module according to claim 1 or 2, characterized in that the said means d insulation include a fuse (3) mounted in series with the electrochemical elements, and a relay (8, 13) controlled by said sensor and whose power circuit (9, 15) closes the series mounting of the elements and the fuse. 4.- The module according to claim 1, 2 or 3, characterized in that this   that the sensors include a pressure switch.   5.- The module according to one of claims 1 to 4, characterized in that   that the sensors include a pressure switch for each element.   6.- The module according to one of claims 3 to 5, characterized in that   the sensors switches are connected in parallel, and in that   the assembly is mounted in series with the coil (7) of said relay (8).   7.- The module according to claim 6, characterized in that the assembly mounted in series with the coil (7) of said relay (8) is mounted at the terminals of said elements.   8.- The module according to one of claims 3 to 5, characterized in that   the sensor switches are connected in series, closed at rest and open in the control position, and in that the assembly controls the coil (7)   of said relay (8) via a transistor.   9.- The module according to one of claims 1 to 8, characterized in that   said sensors are electrically powered sensors.   10.- The module according to claim 9, characterized in that the sensors are chosen from temperature sensors, pressure sensors, sensors detecting overvoltages, undervoltage or short-circuits.   1 1.- The module according to one of claims 1 to 10, characterized in   that the said sensor or sensors comprise a timing circuit.   12.- The module according to one of claims 1, 2, 9 to 11, characterized in that said insulation means comprise a fuse (3) mounted in series with the electrochemical elements, and an electronic controlled switch   by said sensor which closes the series mounting of the elements and the fuse.   13.- The module according to claim 12, characterized in that   the switch is chosen from MOS, transistor, thyristor, IGBT.   14.- The module according to one of claims 3 to 13, characterized in that   that the relay is a bi-stable relay.   15.- Method of protection against malfunction of a battery module comprising at least one electrochemical element (11-16) mounted in series with a fuse (3), at least one sensor (51-56) and a switch controlled by said sensor, the method comprising controlling the switch by the sensor when the sensor detects a malfunction, the switch then closing the series mounting of the elements and the fuse.   16.- The method according to claim 15, characterized in that   The switch remains closed after being controlled by a sensor.   17.- The method according to claim 15 or 16, characterized in that the switch is controlled by the sensor if the malfunction persists   after a timeout period.