Battery management system and method for balancing the charges of the battery cells.

Abstract

This battery management system (1) for an electric vehicle comprises a plurality of slave controllers (7) coupled respectively to a plurality of cells (10) of the battery (2) and a master controller (6) configured to determine charge balancing terms for the cells (10) in an active mode of the management system (1). The management system (1) includes an inactive mode in which the charge balancing terms are determined solely by the slave controllers (7). Figure for abbreviation: Fig 1

Description

Title of the invention: Battery management system and method for balancing the charges of the battery accumulators. Technical field

[0001] The invention relates, in general, to systems for managing a storage battery.

[0002] In particular, the invention relates to wireless management systems for an accumulator battery of an electric vehicle. Previous techniques

[0003] Electric vehicles such as motor vehicles comprise a traction battery and a service battery. The traction battery is the high-voltage battery powering the vehicle's electric motor, while the service battery is the low-voltage battery common to all vehicles, generally 12 or 14 volts, intended to power other functions, such as various on-board equipment of the vehicle.

[0004] A traction battery of an electric vehicle comprises a plurality of accumulators also called cells. Typically, the battery of an electric motor vehicle comprises 96 or more accumulators, grouped into nodes of 8 accumulators. For example, the accumulators of electric or hybrid vehicles are Li-Ion accumulators.

[0005] In order to optimize the life and maintenance of the traction battery as well as its performance, a storage battery management system is used to manage the balancing of the charges of the battery accumulators by discharging the most charged accumulators into a resistor. The objective is for all of the accumulators to be at the same charge level.

[0006] Accumulator battery management systems generally comprise a master controller powered by the low-voltage battery of the vehicle and a plurality of slave controllers. Each slave controller is coupled to a node of a plurality of accumulators which provide its power supply and the master controller comprises a computer determining balancing terms to be applied by each slave controller on the node with which it is coupled in order to balance the charges of the accumulators of the battery.

[0007] In order to limit heating of the resistors, the dissipated power is reduced and the balancing duration is extended. To increase this duration, it is known to carry out periodic wake-ups of the system, in order to restart the balancing of the accumulators. Current management systems therefore include an active mode and a inactive mode. Active mode generally corresponds to turning on the vehicle's ignition and inactive mode corresponds to turning off the vehicle's ignition.

[0008] Document WO2019 / 017595 describes a management system comprising a plurality of slave controllers configured to operate in an active mode and an inactive mode using energy supplied by the battery node to which they are coupled. In the active mode, the slave controllers wirelessly transmit a detection signal indicating a state of the battery node to which they are coupled, and a master controller wirelessly transmits a control signal comprising a balancing term indicating the scanning period and the scanning duration to be performed by the slave controller to discharge the battery node to which it is coupled.

[0009] Generally, the system operation is the same in active and inactive modes. In inactive mode, the master controller sends signals to the slave controllers, but at a lower frequency. Therefore, during inactive mode, the low-voltage battery reduces its autonomy to power the master controller.

[0010] The present invention therefore aims to overcome the aforementioned drawbacks and to propose a system for managing the traction accumulator battery of an electric vehicle comprising an inactive mode which does not cause discharge of the low-voltage battery without losing efficiency.

[0011] The subject of the invention is therefore a system for managing a battery of accumulators of an electric vehicle comprising a plurality of slave controllers coupled respectively to a plurality of accumulators of the battery and a master controller configured to determine terms for balancing the charge of the accumulators in an active mode of the management system, the management system comprising an inactive mode in which the charge balancing terms are determined solely by the slave controllers.

[0012] Advantageously, during the inactive mode each slave controller determines the balancing term of the plurality of accumulators to which it is coupled.

[0013] Advantageously, the master controller is powered by a low-voltage battery and the slave controllers are powered by the traction battery.

[0014] Preferably, the master and slave controllers use wireless communication means.

[0015] The invention also relates to a method for balancing respective charges of accumulators of an accumulator battery of an electric vehicle capable of being implemented by a management system as defined above.

[0016] Advantageously, the master controller communicates the current flowing in the battery to the slave controllers in the active mode, and the method comprises the following steps in an inactive mode:

[0017] - A slave controller becomes a slave-master controller;

[0018] - The slave-master controller requests the other slave controllers the transmission of a minimum voltage among their plurality of accumulators;

[0019] - The slave-master controller sends to each of the other slave controllers a minimum battery voltage among the minimum voltages of the pluralities of accumulators of each slave controller;

[0020] - Each slave controller determines a balancing requirement and a term balancing for its plurality of accumulators;

[0021] Preferably, the method is implemented periodically at very low frequency during inactive mode.

[0022] Advantageously, the step of determining a balancing requirement comprises the determination of state indicators of the plurality of accumulators by said slave controller.

[0023] Preferably, the status indicators include the health status and the charge status of the battery.

[0024] Advantageously, the slave controller becoming the slave-master controller changes with each implementation of the method.

[0025] Thus, the charges of the accumulators associated with each slave controller remain balanced during inactive mode.

[0026] The invention also relates to an electric vehicle comprising a traction battery, a low-voltage battery and a traction battery management system as defined above, the system being capable of implementing a method as defined previously.

[0027] Advantageously, the management system comprises a master controller powered by the low-voltage battery of the vehicle and slave controllers powered by the traction battery.

[0028] Preferably, the active mode corresponds to switching on the vehicle's ignition and the inactive mode corresponds to switching off the vehicle's ignition. Brief description of the drawings

[0029] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0030] [Fig.l] schematically illustrates a management system according to the invention powered by the batteries of an electric vehicle;

[0031] [Fig.2] schematically illustrates the topology of the management system of [Fig.l] in active mode;

[0032] [Fig.3] schematically illustrates the temporal organization of exchanges in active mode of the management system according to [Fig.l] in active mode;

[0033] [Fig.4] schematically illustrates the temporal organization of exchanges in inactive mode of a management system according to the state of the art;

[0034] [Fig.5] schematically illustrates the topology of a management system of [Fig.l] in inactive mode;

[0035] [Fig.6] schematically illustrates the temporal organization of exchanges in inactive mode of the management system according to the invention; and

[0036] [Fig.7] schematically illustrates a balancing method according to the invention. Detailed description of at least one embodiment

[0037] [Fig.l] schematically shows a management system 1 for an accumulator battery 2 according to the invention.

[0038] The storage battery 2 is a storage battery of an electric vehicle, for example an electric traction motor vehicle.

[0039] More precisely, the storage battery 2 is a traction battery of the electric vehicle, that is to say it is the battery powering an electric motor of the electric vehicle. In particular, the traction battery 2 is a high-voltage battery commonly called a battery pack.

[0040] The electric vehicle comprises a low-voltage battery 3 in addition to the traction battery 2.

[0041] The low-voltage battery 3 is a conventional battery present in all vehicles with electric, thermal or hybrid engines, and supplying the various on-board equipment, also called a service battery. The low-voltage battery 3 is generally a 12 Volt battery.

[0042] The electric vehicle comprises a BCM 4, an acronym for the Anglo-Saxon term Body Control Module, which means Vehicle Body Control Module and which is a common name designating an on-board computer controlling electronic accessories of the vehicle such as the air conditioning or the central locking. The electric vehicle further comprises a powertrain supervisor 5 which is controlled by the BCM 4.

[0043] The management system 1 comprises a master controller 6 and a plurality of slave controllers 7.

[0044] The powertrain supervisor 5 controls the powering up of the master controller 6.

[0045] The BCM 4, the supervisor 5 and the master controller 6 are powered by the low-voltage battery 3 via a CAN bus 8, and the plurality of slave controllers 7 are powered by the traction battery 2.

[0046] The management system 1 comprises an active mode corresponding to the ignition of the vehicle being switched on and an inactive mode corresponding to the ignition of the vehicle being switched off. The management system 1 is capable of switching between the active and inactive modes upon the occurrence of a triggering event. For example, the triggering event may be the vehicle stopping at the end of use, i.e. the vehicle being switched off by the user, which causes the switch from active mode to inactive mode. Another triggering event may be the occurrence of the end of charging of the vehicle's traction battery 2.

[0047] [Fig.2] illustrates the topology of the management system 1 in active mode.

[0048] The topology of the management system 1 in active mode is star-shaped around a central gateway 9 coupled to the master controller 6 by the CAN bus 8, and which is powered by the low-voltage battery 3.

[0049] The assembly comprising the master controller 6 and the central gateway 9 communicates wirelessly with the slave controllers 7.

[0050] The traction battery 2 comprises a set of accumulators 10 grouped into several nodes 11. Each slave controller 7 is coupled to a plurality of accumulators 10 forming a node 11.

[0051] For example, the traction battery 2 comprises 96 or 100 accumulators grouped into 12 nodes of 8 accumulators.

[0052] Each slave controller 7 communicates only with the assembly comprising the gateway 9 and the master controller 6.

[0053] In the active mode, the master controller 6 is configured to determine terms for balancing the charge of the accumulators 10. More precisely, the master controller 6 calculates state indicators using data measurements such as the voltage or the temperature in the accumulators 10, and deduces therefrom a balancing term 10 to be applied for each accumulator 10 so as to balance all of the charges of the accumulators 10 of the traction battery 2.

[0054] More precisely, the balancing term intended to balance an accumulator 10 is applied to this accumulator 10 by the slave controller 7 to which it is coupled.

[0055] [Fig.3] illustrates a temporal organization of the exchanges between the controllers of the management system 1 in the active mode. The abscissa axis is a time axis.

[0056] In active mode, the exchanges are chained together at a given PI periodicity, for example 100 milliseconds. The PI period of an exchange is divided into a plurality of time slots, for example equal in duration, typically 3 milliseconds. Synchronization is achieved by sending an initial beacon 6a which is emitted by the master controller 6 via the gateway 9 to all the slave controllers 7. Following this initial beacon 6a, each slot is dedicated to sending information to the assembly comprising the gateway 9 and the master controller 6. This information is sent in a beacon 7a, 7b,... by a slave controller 7 and includes the voltage and temperature measurements of the accumulators to which the slave controller 7 is coupled. Each slave controller 7 therefore knows in which slot it must transmit its information.

[0057] In parallel, the master controller 6 receives the information from each slave controller 7 and determines a balancing term for each accumulator 10 of the battery 2. This balancing term is determined in particular by calculating state indicators relating to the accumulator 10 in question and to the battery 2. These state indicators include the SOH and the SOC, respective acronyms of the English terms “State Of Health” and “State Of Charge”, designating respectively the states of health and charge of the battery 2.

[0058] After determining the balancing term of an accumulator 10, the master controller 6 sends this term to the slave controller 7 to which the accumulator 10 is coupled. This sending is not shown in [Fig.3]. The slave controller 7 then applies this balancing term to the accumulator 10 in question.

[0059] Thus, the charges of the different accumulators 10 of the traction battery 2 are balanced during the active mode.

[0060] The operation of the management system 1 in the active mode is similar to the operation of state-of-the-art management systems in active mode.

[0061] In the example illustrated in [Fig.3], the traction battery 2 comprises 12 accumulator nodes 10, the period PI is 100 milliseconds and the slots are of an equal duration of 3 milliseconds.

[0062] [Fig.4] illustrates a temporal organization of the exchanges between the controllers of a management system according to the state of the art in the inactive mode. The abscissa axis represents the time axis.

[0063] State-of-the-art management systems maintain in the inactive mode the topology illustrated in [Fig.2].

[0064] In the inactive mode of a management system according to the state of the art, the periodicity of the exchanges is extended, for example to a duration P2 of 300 milliseconds. In addition, the exchanges now only include an initial synchronization beacon 6a sent by the master controller 6 to all the slave controllers 7. As long as the beacon 6a does not include a wake-up order, the slave controllers 7 do not send any information. On the other hand, when the beacon 6a includes a wake-up order, the management system of the state of the art carries out an exchange similar to that of the active mode, even if the ignition of the car is switched off. Typically, during the inactive mode, the beacons 6a transmitted do not include a wake-up order for several hours. For example, the wake-up order may occur every eight hours.

[0065] Thus, the inactive mode makes it possible to extend the balancing of the charges of the accumulators and therefore to limit the heating of resistors in which the accumulators discharge according to their balancing term.

[0066] Nevertheless, this inactive mode according to the state of the art requires keeping the gateway 9 switched on and periodically waking up the master controller 6 in order to send the beacons 6a. To wake up the master controller 6, it is necessary to wake up the BCM 4 which wakes up the supervisor 5 which wakes up the master controller 6. The BCM 4, the supervisor 5 and the master controller 6 being powered by the low-voltage battery 3, an overconsumption of the autonomy of this low-voltage battery 3 is induced during the inactive mode.

[0067] [Fig.5] illustrates the topology of the management system 1 according to the invention in inactive mode.

[0068] More specifically, when the management system 1 switches from active mode to inactive mode, its topology is changed from the topology illustrated in [Fig.2] to the topology illustrated in [Fig.5].

[0069] In the inactive mode, the master controller 6 is no longer the coordinator of the network formed by the controllers. Indeed, one of the slave controllers 7 becomes the coordinator of the network and is thus responsible for orchestrating the exchanges in the management system 1. In the following, this slave controller will be called the slave-master controller 12.

[0070] Preferably, the slave controller 7 elected to become the slave-master controller 12 in the inactive mode is chosen according to its position in the battery pack 2. More precisely, it is a slave controller 7 coupled to a central node 11.

[0071] Alternatively, the role of slave-master 12 may change periodically between the slave controllers 7. More specifically, it is possible that at each period of implementation of the method, a different slave controller 7 becomes slave-master controller 12 and sends the synchronization beacon to the other slave controllers 7. Similarly, it is possible that each slave controller 7 must have exercised the role of slave-master controller 12 once before a slave controller 7 becomes master-slave controller 12 a second time. More generally, the slave controller 7 becoming slave-master controller 12 may be designated so that each slave controller successively becomes master slave controller over the course of periodic implementations of the method, and so that each slave controller 7 becomes slave-master controller 12 an equivalent number of times during the inactive mode.This prevents an imbalance between the battery charges of different slave controllers 7, and ensures that all slave controllers 7 have the same power consumption in idle mode. Thus, the battery balance is not affected.

[0072] [Fig.6] illustrates a temporal organization of the exchanges between the controllers of the management system 1 in the inactive mode, and [Fig.7] illustrates a method of balancing the respective charges of the accumulators 10 of the traction battery 2 capable of being implemented by a management system 1.

[0073] The balancing method is implemented by the management system 1 in inactive mode at very low frequency, for example with frames respecting a periodicity P3 of 10 minutes, because the balancing needs evolve very slowly. In this way, the use of the traction battery 2 is economical in the inactive mode.

[0074] In a first step 13, a slave controller 7 becomes a master-slave controller 12. The term "master-slave controller" means that it is one of the slave controllers 7 which becomes the coordinator of the network and of the balancing in inactive mode, this role being occupied by the master controller 6 in the active mode. Thus, in the inactive mode, the slave controllers 7 do not communicate with the master controller 6 but with the master-slave controller 12, and conversely the master controller 6 does not communicate with the slave controllers 7, it is the master-slave controller 12 which does so.

[0075] In a second step 14, the slave-master controller 12 requests the other slave controllers 7 to transmit a minimum voltage among their plurality of accumulators 10.

[0076] More precisely, the slave-master controller 12 sends an initial beacon 15 to all the slave controllers 7 requesting to carry out the voltage measurements of the plurality of accumulators 10 to which they are coupled and to send to the master slave controller 12 the minimum voltage among these measured voltages.

[0077] Each slave controller 7 of the management system is equipped with a computer and sensors enabling it to carry out such operations.

[0078] In a third step 16, the slave-master controller 12 sends to each of the other slave controllers 7 a minimum voltage of the traction battery 2 among the minimum voltages of the pluralities of accumulators of each slave controller 7.

[0079] More precisely, during step 14, the slave-master controller 12 receives all the minimum voltages 17 from each of the accumulator nodes 10 coupled to a slave controller 7, determines the minimum of these received voltages and returns this minimum in a beacon 18 to all the slave controllers 7. In the temporal organization illustrated in [Fig.6], the step of sending the minimum voltages 17 by all the slave controllers 7 takes place in the periodic frame following that of the first initial beacon 15. But it can also take place later or directly following the reception of the first initial beacon 15, each slave controller 7 having to respect its sending slot. The same applies to sending the beacon 18.

[0080] In a fourth step 19, each slave controller 7 determines a balancing requirement and possibly a balancing term for the plurality of accumulators 10 to which it is coupled.

[0081] More precisely, each slave controller 7 receives the minimum voltage of the traction battery 2 in the beacon 18. Furthermore, in the active mode, unlike the state of the art, the master controller 6 transmits the current flowing in the traction battery 2 via the gateway 9 to all the slave controllers 7. The master controller 6 comprises sensors 20 which allow it to determine the current flowing in the battery 2.

[0082] Thus, the slave controllers 7 have the information necessary to determine the status indicators of the plurality of accumulators 10 to which they are coupled. These status indicators are, for example, the state of health or the state of charge of the battery 2.

[0083] To determine whether an accumulator 10 to which a slave controller 7 is coupled needs balancing, the slave controller 7 can perform a comparison between the voltage of the accumulator and the minimum voltage of the battery 2 received in the beacon 18. In the case where the difference between the voltage of the accumulator 10 and the minimum voltage is less than a predetermined threshold S, there is no need for balancing of said accumulator 10 and the balancing term is therefore zero. Conversely, when the difference is greater than the threshold S, there is a need for balancing and the balancing term is determined and then applied by the slave controller 7.

[0084] The threshold S is for example 5 millivolts if the measurement precision is less than 2 millivolts.

[0085] Thus, the balancing requirement and the balancing term are determined in inactive mode only by the slave controllers 7 and not by the master controller 6. In this way, since the slave controllers 7 are powered by the traction battery 2 and not by the low-voltage battery 3, the autonomy of the low-voltage battery 3 is not reduced in inactive mode, since the master controller 6 is not used. In addition, since the traction battery 2 has a long autonomy, it is not a handicap to use it in inactive mode for the use of the slave controllers 7.

Claims

Claims

1. Method for balancing respective charges of accumulators (10) of an accumulator battery (2) of an electric vehicle capable of being implemented by a management system (1) of the accumulator battery (2) of the electric vehicle comprising a plurality of slave controllers (7) respectively coupled to the plurality of accumulators (10) of the battery (2) and a master controller (6) configured to determine terms for balancing the charge of the accumulators (10) in an active mode of the management system (1), the management system (1) comprising an inactive mode in which the balancing terms are determined solely by the slave controllers (7), method in which the master controller (6) communicates the current flowing in the battery (2) to the slave controllers (7) in the active mode, the method comprising the following steps in an inactive mode: - A slave controller (7) becomes a slave-master controller (12);- The slave-master controller (12) requests the other slave controllers (7) to transmit a minimum voltage (17) among their plurality of accumulators (10); - The slave-master controller (12) receives all of the minimum voltages (17), determines the minimum of these received voltages, and returns this minimum in a beacon (18) to each of the other slave controllers (7); and - Each slave controller (7) determines a balancing requirement and a balancing term for its plurality of accumulators (10) by making a comparison between the voltage of the accumulator (10) and the minimum voltage received in the beacon (18); method in which the slave controller (7) becoming the slave-master controller (12) changes at each implementation of the method.;

2. The method of claim 1, wherein the step (19) of determining a balancing need comprises determining status indicators of the plurality of accumulators (10) by said slave controller (7).

3. The method of claim 2, wherein the status indicators comprise the health status and the charge status of the battery (2).

4. A method according to any one of claims 1 to 3, wherein the slave controller (7) becoming a slave-master controller (12) is designated such that each slave controller (7) successively becomes a slave-master controller (12) over the course of periodic implementations of the method, each slave controller (7) becoming an equivalent number of times a slave-master controller (12) during the inactive mode.

5. Electric motor vehicle comprising a traction battery (2), a low-voltage battery (3) and a management system (1) of the traction battery (2) comprising a plurality of slave controllers (7) coupled respectively to the plurality of accumulators (10) of the battery (2) and a master controller (6) configured to determine terms for balancing the charge of the accumulators (10) in an active mode of the management system (1), the management system (1) comprising an inactive mode in which the balancing terms are determined solely by the slave controllers (7), the system (1) being capable of implementing a method according to one of claims 1 to 4.

6. Vehicle according to claim 5, in which the active mode corresponds to the ignition of the vehicle being switched on and the inactive mode corresponds to the ignition of the vehicle being switched off.

7. A vehicle according to claim 5 or 6, wherein the master controller (6) is powered by the low-voltage battery (3) and the slave controllers (7) are powered by the traction battery (2).

8. A vehicle according to any one of claims 5 to 7, wherein the master (6) and slave (7) controllers use wireless communication means.

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