Battery control method

Abstract

Method for controlling at least one electric battery (1) for an aircraft, each battery (1) comprising a plurality of electrical energy storage cells (2) arranged in an enclosure (3), the method comprising steps of: - detecting the start of thermal runaway in the enclosure (3) by means of at least one sensor (11) arranged in the enclosure (3), - supplying heat to the enclosure (3) so as to increase a temperature in the enclosure (3), by means of at least one heating device (6, 7). Figure to be published with the abstract: 1

Description

Title of the invention: Battery control method Technical field of the invention

[0001] The invention relates to a method for controlling at least one electric battery for an aircraft. State of the prior art

[0002] The use of on-board batteries in an aircraft allows the supply of electrical energy to secondary systems such as on-board computers, lighting and ventilation of the passenger compartment, etc. These functions are very important for flight safety and it is desirable that the electrical supply is maintained even in the event of a malfunction of some of the batteries.

[0003] In addition, the development of electrically powered aircraft places emphasis on the management of said batteries, which in this case are responsible for powering the propulsion systems. Maintaining the proper functioning of these propulsion systems is therefore particularly critical.

[0004] On-board battery systems are generally composed of a plurality of battery packs contained in separate protective and insulating enclosures. Such a battery comprises several electrochemical cells, in particular Li-ion cells, electrically connected in parallel and making it possible to store electrical energy.

[0005] These cells may be subject to thermal runaway, during which the internal temperature of the cell increases sharply, which leads to emissions of heated gases and a melting of certain constituents of the cell leading to its destruction and the ejection of debris. This thermal runaway presents a risk of propagation to neighboring cells, then to the entire battery pack, and may even propagate in certain cases to neighboring batteries.

[0006] This runaway phenomenon can be triggered by three types of initiation: thermal (for example following an increase in temperature in the enclosure due to an external cause), electrical (for example due to an overload due to a malfunction of the aircraft's electrical system), mechanical (for example following an impact or deformation of the enclosure) or even following an internal defect in the Li-ion cell.

[0007] Once the runaway of the first cell has been initiated, a significant production of heat and hot gas is induced, which can lead to more abrupt phenomena such as combustion and explosion of the initiated cell. All of this leads to the propagation of the thermal runaway to neighboring cells.

[0008] Thermal runaway is based on several degradation mechanisms at the cell level such as degradation of the interface at the anode of the cell, then degradation of the electrolyte at the electrodes and melting of the separator inducing a new internal short circuit. Other mechanisms, for example oxygen crossover, can be added to these, for example in the case of lithium metal cells.

[0009] These mechanisms induce the high production of heat, hot liquids and gases. These gases can be degraded by combustion, or lead to explosions in the event of uncontrolled combustion.

[0010] Currently, during thermal runaway of a Li-ion battery, battery cooling procedures are implemented in order to limit the thermal runaway. These methods tend to slow down the propagation of the thermal runaway most of the time in order to reduce its intensity or in some cases even make it possible to stop it (in particular in the case where Li-ion cells with low reactive chemistry are used because their critical temperature for triggering the thermal runaway is high).

[0011] These active countermeasures are generally implemented upon detection of the onset of thermal runaway, which is detected by sudden variations in temperature or electrical voltage in the battery.

[0012] Other solutions are used to enable the control and / or reduction of thermal runaway such as cutting off the power supply (to limit the energy input), the use of thermal insulating walls to limit the propagation of heat or even anti-debris walls in order to protect the cells from debris and jets of molten material emitted by a Li-ion cell undergoing thermal runaway.

[0013] However, thermal runaway is a random phenomenon, which makes it difficult to control. Indeed, during tests aimed at determining the temperatures at which thermal runaway triggers or the propagation speed depending on the characteristics of the batteries and external conditions, a very large dispersion of values ​​is observed.

[0014] This strong dispersion makes it very difficult to design mitigation solutions to contain thermal runaway and limit its propagation. Presentation of the invention

[0015] The invention aims to remedy these drawbacks, by enabling mitigation of the effects of thermal runaway and by controlling propagation in the battery.

[0016] To this end, the invention relates to a method for controlling at least one electric battery for an aircraft, each battery comprising a plurality of cells of electrical energy storage arranged in an enclosure, the method comprising steps of:

[0017] - detection of the start of thermal runaway in the enclosure by means of at least one at least one sensor placed in the enclosure,

[0018] - supply of heat into the enclosure so as to increase a temperature in the enclosure, by means of at least one heating device.

[0019] Such a method makes it possible to reduce the criticality of thermal runaway by the controlled supply of heat to the battery. Thus, the control of thermal runaway is simplified and its consequences are less serious.

[0020] The heating device is adapted to provide heat into the enclosure on command.

[0021] The heating device is for example adapted to provide a heat flow towards the enclosure, determined in such a way that an average temperature variation in the enclosure is greater than or equal to 5°C per minute, for the duration of the heat supply step.

[0022] The cells are in particular electrochemical type cells, for example lithium-ion cells.

[0023] The method is for example implemented by an electronic control module, comprising a processor and a memory and controlling each sensor.

[0024] Each sensor may be selected from a temperature sensor, a pressure sensor, an electric current sensor, an electric voltage sensor, a gas flow detector and a gas detector.

[0025] Such a sensor makes it possible to detect the start of thermal runaway in the battery quickly and reliably.

[0026] The gas detector is for example a CO, CO2, H2 and / or HF detector.

[0027] Each sensor is for example controlled by the control module.

[0028] The heating device may comprise a pipe connecting the enclosure to a hot air duct, said pipe being provided with a closing member.

[0029] Such a feature makes it possible to sweep the enclosure with a flow of hot air so as to bring heat to the battery and to purge gases emitted by the cells during racing.

[0030] The shut-off member is, for example, a solenoid valve controlled by the control module.

[0031] The closure member may comprise a fusible closure element, capable of breaking under the action of a high temperature and / or pressure in the enclosure.

[0032] Such a feature allows the heat supply to be triggered mechanically, without requiring electrical or electronic control.

[0033] The heating device may comprise at least one heat pipe thermally connecting the enclosure and a heat source.

[0034] Such a feature allows heat input without requiring gas flow into and out of the enclosure.

[0035] The heat pipes are for example isolated from the heat source by insulation means controllable by the control module.

[0036] The heating device may comprise at least one active heat supply element arranged in the enclosure.

[0037] Such a feature makes it possible to bring heat directly into the enclosure without using an external device.

[0038] The active heat supply element is for example a heating resistor or a heating panel, controlled by the control module.

[0039] The active heat supply element may comprise a chemical filler capable of reacting exothermically once initiated.

[0040] Such a characteristic allows the heat supply to be maintained even in the event of deterioration of the contents of the enclosure preventing the supply of electricity.

[0041] A heat flux to the enclosure may be determined such that an average temperature variation in the enclosure is greater than or equal to 20°C per minute for the duration of the heat supply step.

[0042] Such a temperature variation value makes it possible to better reduce the criticality of the thermal runaway by limiting the total energy emitted, the maximum heat emitted and / or the maximum temperature reached in the enclosure during the thermal runaway.

[0043] The invention also relates to a device for implementing the preceding method, the device comprising:

[0044] - at least one electric battery for aircraft, each battery comprising a plurality of electrical energy storage cells arranged in an enclosure,

[0045] - at least one sensor arranged in the enclosure,

[0046] - a heating device capable of providing heat into the enclosure on order, and

[0047] - a control module configured to control the heating device and / or each sensor. Brief description of the figures

[0048] [Fig-1] [Fig.l] is a schematic view of a battery and control system configured to implement a method according to the invention,

[0049] [Fig.2] [Fig.2] is a schematic view of the implementation of the method according to the invention on the battery of [Fig.l],

[0050] [Fig.3] [Fig.3] is a graphical representation of a total energy released and a maximum heat reached in a battery, as a function of a heating rate, during the implementation of a method according to the invention,

[0051] [Fig.4] [Fig.4] is a graphical representation of a maximum temperature reached in a battery, as a function of a heating rate, during the implementation of a method according to the invention,

[0052] [Fig.5] [Fig.5] is a schematic view of a battery and a control system for implementing a method according to a second embodiment of the invention,

[0053] [Fig.6] [Fig.6] is a schematic view of a battery and a control system for implementing a method according to a third embodiment of the invention,

[0054] [Fig.7] [Fig.7] is a schematic view of the implementation of the method according to the third embodiment of the invention on the battery of [Fig.6],

[0055] [Fig.8] [Fig.8] is a schematic view of a battery and a control system for implementing a method according to a fourth embodiment of the invention, Detailed description of the invention

[0056] A first embodiment of a control method according to the invention is described with reference to Figures 1 and 2.

[0057] [Fig.l] represents a battery 1 comprising a plurality of lithium-ion (Li-ion) type cells 2 arranged in an enclosure 3. This battery 1 is for example installed on an aircraft for the supply of electrical energy to propulsion and / or support functions.

[0058] A first opening 4 is provided in the enclosure 3 and connected to a hot air passage conduit 5 by a pipe 6 provided with a first valve 7, so as to allow the entry of hot air into the enclosure 3 by opening said first valve 7. The pipe 6 and the valve 7 thus constitute a controllable heating device for the enclosure 3.

[0059] The duct 5 is for example a hot air duct of the avionics system, usually present on an aircraft.

[0060] A second opening 8 provided with a second valve 9 opens in the enclosure 3 and opens outside the enclosure 3, so as to purge the gases contained in the enclosure 3 and to allow the circulation of hot air through the enclosure 3 when the first valve 7 is also open.

[0061] A control module 10 is connected to the first valve 7 and to the second valve 9, which are for example solenoid valves, so as to control their opening and closing automatically.

[0062] The control module 10 is also connected to at least one sensor 11 configured to measure at least one parameter characteristic of the thermal runaway of the battery 1.

[0063] In the example shown, the control module 10 is connected to a temperature sensor 11 and a pressure sensor 11 arranged in the enclosure 3.

[0064] These sensors 11 are capable of detecting the start of thermal runaway of the battery 11, the thermal runaway causing a rise in the temperature in the enclosure 3 and an emission of gas increasing the pressure in the enclosure 3.

[0065] Other types of sensors allow thermal runaway to be detected by measuring characteristic parameters.

[0066] For example, gas detector type sensors, configured to detect significant levels of CO, CO2, H2 and / or HF in the enclosure 3 make it possible to detect the emission of gas characteristic of thermal runaway.

[0067] Alternatively, a voltage sensor 11 measuring the variations in the voltage at the terminals of the battery 1, or a current sensor 11 measuring the delivered electric current, can make it possible to detect the start of thermal runaway.

[0068] Alternatively, sensors 11 for measuring voltage or temperature directly at the level of the cells 2 or the cell lines 2 can make it possible to detect the start of thermal runaway.

[0069] Increasing the number of sensors 11 and associated measured parameters allows for finer and faster detection of thermal runaway, and allows for reducing the number of cases of erroneous detection.

[0070] The control module 10 is configured to monitor the evolution of the characteristic parameters measured by the sensors 11, detect the start of thermal runaway of the battery 11 from this evolution, and trigger a heat supply into the enclosure 3 when the start of thermal runaway is detected.

[0071] This heat input is shown in [Fig.2]. A faulty cell 2a experiences the start of thermal runaway and releases heat and heated gases into the enclosure 3. The associated temperature rise and overpressure are detected by the temperature and pressure sensors 11 and the control module determines the presence of the start of thermal runaway in the enclosure.

[0072] The control module 10 then commands the opening of the first valve 7 and the second valve 9, which allows the entry into the enclosure 3 of hot air coming from the conduit 5, and the exit through the second opening 8 of this hot air after it has circulated in the enclosure, as well as the purging of the heated gases emitted by the faulty cell 11.

[0073] The introduction of a flow of hot air into the enclosure 3 makes it possible, in addition to purging part of the gases, to supply heat regularly to the cells 2 of battery 1. Such a regular and controlled supply of heat allows control of the thermal runaway phenomenon by removing its random effects.

[0074] Indeed, in cases of uncontrolled runaway, very varied propagation durations can be obtained with the same battery and therefore the battery could in certain cases see sustained high temperatures over a very long time, which then makes it difficult to contain the runaway.

[0075] Conversely, rapid and controlled initiation of thermal runaway makes it possible to reduce the occurrence of critical phenomena, such as explosions or very high temperatures.

[0076] Furthermore, a rapid increase in temperature during controlled runaway further reduces runaway responsiveness, counterintuitively even for those skilled in the art.

[0077] These effects are highlighted by the experimental results shown in Figures 3 and 4.

[0078] [Fig.3] is a graphical representation of a total energy E emitted by a Li-ion cell during the entire thermal runaway (solid curve with round dots, in kilojoules) and a maximum heat release HR (dotted curve with square dots, in kilowatts) during this thermal runaway, as a function of a temperature increase rate dT / dt (in °C per minute) in the battery.

[0079] The rate of increase in temperature dT / dt is a variation in the average temperature in the battery, directly proportional to the heat flux supplied to the battery during thermal runaway.

[0080] There is a clear trend towards a reduction in both the total energy E and the peak heat emitted HR when the temperature increase rate dT / dt is high. Thermal runaway is therefore better controlled and presents less acute criticality with a significant external heat input.

[0081] [Fig.4] is a graphical representation of the maximum temperature Tmax (in °C) measured in the battery during thermal runaway, as a function of the previously defined temperature increase rate dT / dt.

[0082] A reduction in the maximum temperatures reached during thermal runaway is observed with a rapid increase in the average temperature of the battery, with maximum temperatures maintained below 600°C for a very rapid initiation of runaway.

[0083] These developments show that significant external heat inputs, resulting in average temperature ramps greater than or equal to 20°C / min, greatly limit the criticality of thermal runaway and facilitate its control.

[0084] A proposed mechanism for this phenomenon is that the contribution of significant heating makes it possible to bypass the stages of degradation of the solid electrolytic interphase (or SEI, for Solid Electrolyte Interphase in English) and of decomposition of the electrolyte to directly trigger the melting phase of the separator between electrodes. A temperature peak is thus reached more quickly, limiting the energy supplied to the rest of the system over all the preceding exothermic stages and therefore reducing the overall quantity of energy to be contained and the protection time to be ensured.

[0085] The reduction in the maximum temperatures reached makes it possible to reduce the size and mass of the thermal protections of the enclosure, which will be exposed to extreme temperatures for a shorter time.

[0086] A second embodiment of the control method according to the invention is described with reference to [Fig.5], with a different method of supplying external thermal energy.

[0087] In this second embodiment, the first valve 7 controlled by the control module 10 is replaced by a fusible plug element 12 plugging the pipe 6. The fusible plug element 12 is for example a membrane made from a material having a predetermined melting temperature so that the fusible plug element 12 does not melt at the temperature of the hot air in the pipe 6, but melts when it is exposed to heated gases emitted during thermal runaway of one of the cells 2.

[0088] The melting of the fusible plug element 12 allows the entry of hot air from the conduit 5 through the pipe 6, as in the previous embodiment.

[0089] Such a fusible plug element 12 makes it possible to trigger the mitigation even in the event of failure of the control module 10 or the sensors 11.

[0090] The second valve 9 can also be replaced by a similar fusible shut-off element.

[0091] A third embodiment of the method according to the invention is shown in Figures 6 and 7, implementing another means of supplying external heat.

[0092] In this third embodiment, the opening 4, the pipe 6 and the valve 7 are not present.

[0093] Instead, a hot source 13 located near the enclosure 3 is connected to said enclosure 3 by a plurality of heat pipes 14. The hot source 13 is a hot part of the aircraft, for example an avionics system or an electronic power source.

[0094] The heat pipes 14 are made of thermally conductive material, for example metallic, and extend through the walls of the hot source 13 and those of enclosure 3, so as to conduct the heat from the hot source towards the interior of enclosure 3.

[0095] Each heat pipe 14 comprises a first end 15 extending inside the walls of the heat source 13, insulated from the heat by a secondary wall 16. The secondary wall 16 surrounds the first ends 15 so as to thermally insulate them from the heat source 13, as shown in [Fig.6].

[0096] This secondary wall 16 can open under control of the control system 10, for example by means of a valve, a flap or a sliding panel.

[0097] In the method according to the third embodiment, the detection of the start of thermal runaway by the control system 10 by means of the sensor 11 causes the said control system 10 to issue a command to open the secondary wall 16, as shown in [Fig.7].

[0098] The first end 15 of each heat pipe 14 is then exposed to the heat from the heat source 13. This heat is conveyed through the heat pipes 14 to the interior of the enclosure 3, constituting the external heat supply to the battery 1.

[0099] A fourth embodiment is shown in [Fig.8].

[0100] In this embodiment, an active heat supply element 19 is arranged inside the enclosure 3, and is controlled by the control system 10.

[0101] The active heat supply element 19 is for example a heating resistor or a heating pad, installed in the enclosure in order to implement the method according to the invention or forming part of a pre-existing temperature control system in the enclosure 3.

[0102] Such a temperature control system of the enclosure 3 is sometimes installed in battery enclosures arranged in a cold environment of the aircraft, because such batteries exhibit optimal operation above a minimum temperature.

[0103] In the method according to the invention, the active heat supply element 19 is triggered by the control system 10 in response to the detection of the start of thermal runaway in the enclosure 3, as previously described, so as to allow an external heat supply reducing the criticality of the thermal runaway.

[0104] Several active heat supply elements 19 can be arranged in the enclosure 3 if necessary, in order to increase the heat supply in the enclosure 3 and / or to make it more regular.

[0105] According to a variant of the fourth embodiment, the active heat supply element 19 is a consumable element, for example a chemical charge capable of undergoing an exothermic chemical reaction on command from the control module 10. Such a chemical charge makes it possible to maintain the heat supply throughout the duration of the thermal runaway, even in the event of damage to the contents of the enclosure by the runaway, since no electricity supply is necessary once the chemical reaction has started.

[0106] Each of the heat supply methods and the associated heating devices can be used independently of each other and in combination, depending on the operational conditions, in a manner determined by a person skilled in the art.

Claims

Claims

1. Method for controlling at least one electric battery (1) for an aircraft, each battery (1) comprising a plurality of electrical energy storage cells (2) arranged in an enclosure (3), the method comprising steps of: - detecting the start of thermal runaway in the enclosure (3) by means of at least one sensor (11) arranged in the enclosure (3), - supplying heat to the enclosure (3) so as to increase a temperature in the enclosure (3), by means of at least one heating device (6, 7, 14, 19).

2. Method according to the preceding claim, in which each sensor (11) is chosen from a temperature sensor, a pressure sensor, an electric current sensor, an electric voltage sensor, a gas flow detector and a gas detector.

3. Method according to one of the preceding claims, in which the heating device (6, 7) comprises a pipe (6) connecting the enclosure to a hot air duct, said pipe (6) being provided with a closing member (7).

4. Method according to the preceding claim, in which the closure member (7) comprises a fusible closure element (12), capable of breaking under the action of a high temperature and / or pressure in the enclosure.

5. Method according to one of the preceding claims, in which the heating device comprises at least one heat pipe (15) thermally connecting the enclosure (3) and a heat source (13).

6. Method according to one of the preceding claims, wherein the heating device (19) comprises at least one active heat supply element (19) arranged in the enclosure (3).

7. A method according to the preceding claim, wherein the active heat supply element (19) comprises a chemical filler capable of reacting exothermically once initiated.

8. Method according to one of the preceding claims, in which a heat flow towards the enclosure (3) is determined so that an average temperature variation in the enclosure (3) is greater than or equal to 20°C per minute, for the duration of the heat supply step.

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