Method for estimating the state of health of a battery and vehicle suitable for implementing this method

Abstract

The invention relates to a method for estimating a state of health related to the resistance of electrochemical cells of a storage battery (6) equipping a motor vehicle (1) and configured to power an inverter (5) of an electric machine of the motor vehicle, said inverter being controlled, in a Park frame linked to a rotor of the electric machine, by a direct stator current, a quadratic stator current, and a rotor current, the method comprising: - a step of generation, by the storage battery, of a step of direct stator current, - a step of determining an internal resistance value, - a step of estimating a value representative of the state of health as a function of the determined internal resistance value, The invention further relates to a motor vehicle configured to implement this method. Figure for abstract: Fig.1

Description

Title of the invention: Method for estimating the state of health of a battery and vehicle suitable for implementing this method Technical field of the invention

[0001] The present invention relates generally to storage batteries, in particular storage batteries fitted to motor vehicles, for example electric or hybrid vehicles.

[0002] The invention relates in particular to a method for estimating the state of health linked to the resistance of electrochemical cells of an accumulator battery equipping a motor vehicle. State of the art

[0003] The aging of the electrochemical cells of a storage battery equipping electric or hybrid motor vehicles is manifested in particular by a loss of charging capacity and power. It significantly affects the overall performance of the storage battery, and therefore of the vehicle equipped with it.

[0004] For example, the aging of an electrochemical cell causes an increase in its internal resistance, which contributes to the loss of power. The increase in this internal resistance can be characterized by a parameter called "state of health resistance", commonly abbreviated SOHR (for "State Of Health Resistance", in English). The state of health resistance is expressed as a percentage increase in the resistance of the electrochemical cells compared to the initial resistance of the cells (called "at the beginning of life"). Thus, the SOHR will be equal to 100% at the beginning of the life of the cells, and will increase as the cells age (for example, it will be equal to 130% after five years).

[0005] There are different methods for estimating the state of health related to resistance. Some are based on an a priori estimation of the electrochemical evolution of the battery which takes into account in particular pre-established models of durability, the time spent by the battery in different states of charge and at different temperatures. These methods have the disadvantage of not allowing detection of abnormal phenomena which appear with the aging of the battery, such as an internal short circuit. Other methods are based on electrochemical impedance spectroscopy (EIS). These methods have the disadvantage of having to be carried out outside the operation of the vehicle (in a garage or laboratory), possibly with removal of the storage battery, and therefore do not allow on-board operation.

[0006] Generally speaking, existing SOHR estimation methods lack precision. They do not take into account factors such as charging speeds or the type of vehicle driving, nor the different temperature gradients within the battery. Presentation of the invention

[0007] In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes a method for estimating the SOHR which is precise and allows for on-board implementation in the vehicle.

[0008] More particularly, according to the invention, there is proposed a method for estimating a state of health linked to the resistance of electrochemical cells of a storage battery configured to power an inverter of an electrical machine, said inverter being controlled, in a Park frame linked to a rotor of the electrical machine, by a direct stator current, a quadratic stator current, and a rotor current, the method comprising: - a step of generation, by the accumulator battery, of a current step supplying said inverter, - a step of determining, for at least one electrochemical cell of the storage battery, an internal resistance value of the electrochemical cell from a voltage measured at the terminals of the electrochemical cell and the value of the current step, - a step of estimating, for said at least one electrochemical cell, the state of health as a function of the determined internal resistance value, the current step being generated from the direct stator current, while the quadratic stator current is zero.

[0009] Generating the current step from the direct stator current advantageously allows the method to be implemented on board the vehicle. This therefore eliminates the need for tedious maintenance operations, such as removing the battery. This also allows a greater number of measurements to be taken and therefore a more precise estimate of the state of health related to the resistance to be obtained. Furthermore, performing the voltage step when the quadratic stator current is zero has the advantage of not creating any motor torque.

[0010] Other advantageous and non-limiting characteristics of the method according to the invention, taken individually or in all technically possible combinations, are the following: - the current step has a minimum amplitude of 10 amperes. - the process is implemented automatically by a control system of the electric motor vehicle while the vehicle is stationary. - the accumulator battery equips a motor vehicle comprising said electric machine, the method is implemented upon detection of activation of a parking mode of the electric motor vehicle or upon detection of a request to start the motor vehicle. - prior to generating the current step, the method comprises a step of determining a state of charge, the step of estimating the state of health being implemented only for a state of charge included in a predetermined range of acceptable values. - the predetermined acceptable range of values ​​for the state of charge includes any state of charge value greater than or equal to 25% of the maximum state of charge. - the method comprises a step of recording, in a computer memory, the determined value of internal resistance, the step of estimating the state of health linked to the resistance being a function of said determined value recorded in the computer memory as well as at least one other determined value recorded in the computer memory during a previous iteration of the method. - the step of determining the health status linked to the resistance involves establishing an average of the determined values ​​of the internal resistance recorded in the computer memory. - the accumulator battery equips a motor vehicle comprising said electric machine the motor vehicle is equipped with a plurality of computers, including a first computer configured to control and supervise the inverter, a second computer is configured to control and supervise the battery, the step of generating the current step being implemented by the first computer upon receipt of a control signal from the second computer, the step of calculating the internal resistance and the step of estimating the state of health linked to the resistance being implemented by the second computer.

[0011] The invention also proposes an electric or hybrid motor vehicle equipped with a storage battery and comprising a control system configured to implement the method according to the invention.

[0012] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0013] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0014] In the attached drawings:

[0015] [Fig-1] is a schematic view of an architecture of a motor vehicle according to the invention;

[0016] [Fig.2] illustrates a mode of implementation of the method according to the invention;

[0017] [Fig.3] represents, on a first graph, the generation of a current step by the accumulator battery of the motor vehicle according to the invention and, on a second graph, the voltage response of this battery.

[0018] The method according to the invention aims to estimate a state of health linked to the resistance of electrochemical cells of a storage battery of an electric or hybrid motor vehicle. Such a motor vehicle, designated by the general reference 1 in [Fig.l], can be of any type (car, truck, bus, ship, airplane, etc.). It comprises a powertrain 3 and a control system 2 for this powertrain 3.

[0019] The powertrain 3 comprises in particular an electric machine 4, an inverter 5 and a storage battery 6. The inverter 5 is configured to transform and transmit the electric current supplied by the storage battery 6 to the electric machine 4. It will be noted that the powertrain 3 could possibly comprise an internal combustion engine and / or another electric machine.

[0020] The electrical machine 4 can be of any type (axial or radial flux, wound rotor or permanent magnets, etc.). In any case, it comprises at least one stator fixedly mounted on the chassis of the motor vehicle, and a rotor adapted to rotate relative to the stator around an axis of rotation.

[0021] In this example, the control system 2 comprises several computers conventionally present in motor vehicles or hybrid vehicles, but which are here configured for the implementation of the method according to the invention. Each computer comprises a processor and a computer memory, as well as communication interfaces, for example connected to an analog / digital conversion network (CAN) of the motor vehicle 1. A first computer 7 (commonly referred to as HEVC, for “Hybrid and Electric Vehicle Controller”) is configured to supervise the powertrain 3. A second computer 8 (commonly referred to as “Inverter Electronic Control Unit”, or “Inverter ECU”) is configured to control and supervise the inverter 5.A third computer 9 (commonly referred to by the English acronym BMS, for “Battery Management System”) is configured to control and supervise the accumulator battery 6. A fourth computer 10 (commonly referred to by the English acronym BCM, for “Body Control Module”) is configured to control and supervise the systems (not shown) associated with the bodywork of the . vehicle 1 or, more generally, systems which do not directly concern the powertrain (electric windows, alarms, mirror controls, door locks, etc.)

[0022] The control of the electrical machine 4 is here considered in a Park frame of axes d, q. The Park transform makes it possible to model the three-phase system of the electrical machine 4, conventionally presented in a fixed frame linked to the stator, by a two-phase system in a rotating frame linked to the rotor. Thus, the control of the stator is not presented as a triplet of alternating currents phase-shifted by 120°, but as a pair of direct currents. A first stator current, or direct stator current Id, corresponds to the stator current projected onto the direct axis of the rotor (conventionally called the “d axis”) which is parallel to the rotor coil. A second stator current, or quadratic stator current Iq, corresponds to the stator current projected onto the quadrature axis of the rotor (conventionally called the “q axis”) which is perpendicular to the rotor coil. The control of the rotor is presented by a single rotor current If.

[0023] In this Park frame, the torque Ce applied to the rotor is given by the following equation:

[0024] [Math.l] Ce = ^(cd IdJ q - LqIdJq + MflfJq}

[0025] With Ld and Lq the stator inductances on the d and q axes of the Park frame (not equal in a salient pole machine), Mf the mutual inductance between the rotor and the stator and p the number of stator pole pairs.

[0026] As illustrated in [Fig. 2], the motor vehicle 1 equipped with the control system 2 is particularly suitable for implementing the method according to the invention. According to the example illustrated, an initial step E1 of the method comprises a detection, here by the first computer 7, of an end of mission of the vehicle. By "mission of the vehicle" is meant here a journey made by the motor vehicle or, in other words, a period of driving. For example, the end of mission corresponds to the activation of a parking mode of the motor vehicle. The engine of the motor vehicle (or, where appropriate, the engines) is therefore switched off. Upon detection of the end of mission, the first computer 7 sends a control signal to the third computer 9.

[0027] During a second step E2, upon receipt of the control signal, the third computer 9 evaluates the state of charge of the storage battery 6. Indeed, the inventors have observed that when the storage battery 6 has a low state of charge (SOC), for example a state of charge less than 25% of the maximum charge, then the internal resistance DCR of the cells electrochemical varies very strongly with the state of charge. Thus, the implementation of the method can be inhibited when the state of charge is lower than the predetermined threshold (in other words, a state of charge value at least equal to the predetermined threshold is a necessary condition for the implementation of the method as a whole). If the conditions are favorable to the continuation of the method, for example if the state of charge is higher than a predetermined charge threshold, then the method continues with a third step E3 which includes sending, by the second computer 8, a request for estimation of the SOHR to the third computer 9.

[0028] During a fourth step E4, in response to the estimation request, the third computer 9 commands a generation, by the accumulator battery 6, of a current step supplying said inverter, here a direct stator current step Id. Since the vehicle 1 is stationary, the quadratic stator current Iq is zero; the torque Ce applied to the rotor therefore remains zero regardless of the value of the direct stator current Id. Here, the rotor current If is also zero.

[0029] The amplitude of the current step is for example chosen so as to respect a compromise between a large amplitude step, which would allow great precision, and a smaller amplitude step, which would allow the current consumption to be reduced. This compromise takes into account in particular the maximum current of use of electrochemical cells, which varies according to the configuration of the motor vehicle and the envisaged applications. The current step has an amplitude of at least 10 amperes in absolute value and preferably less than or equal to 30 amperes in absolute value, and a duration of at least 500 milliseconds. For example, as illustrated in the upper graph of [Fig.3], the current step has a value of -30 amperes and a duration of 30 seconds.

[0030] The current step is used to determine the internal resistance, or direct current resistance (DCR) of each electrochemical cell of the storage battery, from the voltage across the terminals of the electrochemical cell during the current step Id, which is illustrated here in the lower graph of [Fig.3]. A voltage drop of approximately 0.3 volts is observed during the current step.

[0031] A fifth step E5 comprises a detection and an acquisition, by the third computer 9, of the current step Id and the voltages at the terminals of each of the electrochemical cells. For example, the acquisition of the voltage is carried out after a duration equal to a fraction of the duration of the step, for example 25%, or after a duration substantially equal to the duration of the voltage step. The third computer 9 then calculates (step E6) the respective internal resistances DCR of the cells. Here, the internal resistance DCR of any electrochemical cell i of the storage battery is given by the following formula:

[0032] [Math.2]

[0033] With AV(i) the voltage variation at the terminals of this cell during the duration of the step and AI the amplitude of the current step Id.

[0034] The health states linked to the resistance are then estimated (step E7) as a function of the calculated internal resistances DCRi and a predetermined value of DCR, called the “beginning of life” value, or DCRbol (“Beginning Of Life”, in English), according to the following formula:

[0035] [Math.3]

[0036] The values ​​of internal resistance DCR and state of health linked to the resistance SOHR are for example stored, during an eighth step E8, in a computer memory of the control system 2 of the motor vehicle 1.

[0037] In a final step E9, the third computer 9 calculates a state of health related to the overall SOHR resistance of the storage battery 6 from the state of health values ​​related to the SOHR resistance recorded in the computer memory, for example by averaging operations. Alternatively, the final step E9 is only implemented if the number of values ​​recorded in the computer memory is sufficient to calculate the state of health related to the overall SOHR resistance. For example, a predetermined number can be defined, which corresponds to a number of prior implementations of the method.

[0038] Thanks to the method described above, in particular thanks to its implementation at the end of each mission, a large number of measurements are available making it possible to improve the precision of the estimation of the state of health linked to the resistance, the SOHR state of health of each cell and that of the battery being able to be updated according to the new measurements.

[0039] The present invention is in no way limited to the embodiment described and represented above in connection with figures 1 to 3, and those skilled in the art will be able to provide any variant in accordance with the invention.

[0040] For example, an implementation of the method has been described at the end of the period of driving of the motor vehicle (end of mission). According to a variant, the method can be implemented after a period of stopping of the vehicle, for example when starting the motor vehicle or when detecting the unlocking of the doors of the motor vehicle. In this case, in order not to delay the starting of the vehicle, the duration of the current step can be chosen to be shorter, for example equal to 500 milliseconds.

[0041] An implementation of the method conditioned on a state of charge of the battery above a predetermined threshold. Alternatively, it is possible for the method to be implemented regardless of the battery state of charge, but for the values ​​measured while the battery state of charge is below the predetermined threshold not to be recorded in the computer memory

[0042] According to a variant, the method according to the invention is implemented at the end of a predetermined time after a period of stopping of the motor vehicle. In the case of stopping of the vehicle, the control system 9, with the exception of the fourth computer 10, is switched off. The fourth computer 10 is then configured to wake up the control system at the end of the predetermined time in order to start the implementation of the method. The initial step E1 therefore comprises in this case the sending by the fourth computer 10 of a wake-up signal, or switching on signal, to the first computer 7, which itself will command the switching on of the other computers 8, 9 of the motor vehicle 1.

[0043] The inventors have observed that the internal resistance value DCR increases with the decrease in the temperature of the battery. Thus, according to one embodiment, the measured internal resistance values ​​DCR are grouped, at the time of their recording in the computer memory, according to the temperature of the battery, for example grouped by predetermined temperature ranges (for example ranges of three degrees). The estimation of the state of health linked to the SOHR resistance can then be carried out separately for each temperature or each temperature range.

Claims

Claims

1. Method for estimating a state of health (SOHR) linked to the resistance of electrochemical cells of a storage battery (6) configured to power an inverter (5) of an electric machine (4), said inverter (5) being controlled, in a Park frame linked to a rotor of the electric machine, by a direct stator current (Id), a quadratic stator current (Iq), and a rotor current (If), the method comprising: - a step of generating, by the storage battery (6), a current step supplying said inverter (5), - a step of determining, for at least one electrochemical cell of the storage battery (6), an internal resistance value (DCR) of the electrochemical cell from a voltage measured at the terminals of the electrochemical cell and the value of the current step, - a step of estimating, for said at least one electrochemical cell,of a value representative of the state of health (SOHR) as a function of the determined internal resistance value (DCR), characterized in that the current step is generated from the direct stator current (Id), while the quadratic stator current (Iq) is zero.,

2. The method of claim 1, wherein the current step has a minimum amplitude of 10 amperes.

3. Method according to claim 1 or 2, wherein the accumulator battery (6) equips a motor vehicle (1) comprising said electric machine (4), the method being implemented automatically by a control system (2) of the motor vehicle (1) while the motor vehicle (1) is stationary.

4. Method according to claim 3, which is implemented upon detection of activation of a parking mode of the electric motor vehicle or upon detection of a request to start the motor vehicle.

5. Method according to any one of claims 1 to 4, comprising, prior to the generation of the current step, a step (E2) of determining a state of charge of the accumulator battery (6), the step of estimating the state of health (SOHR) being implemented only for a state of charge included in a range of values predetermined acceptable.

6. The method of claim 5, wherein the predetermined acceptable range of values ​​for the state of charge includes any state of charge value greater than or equal to 25% of the maximum state of charge.

7. Method according to any one of claims 1 to 6, comprising a step of recording, in a computer memory, the determined value of internal resistance (DCR), the step of estimating the state of health linked to the resistance being a function of said determined value recorded in the computer memory as well as at least one other determined value recorded in the computer memory during a previous iteration of the method.

8. Method according to claim 7, in which the step (E7) of determining the state of health (SOHR) comprises establishing an average of the determined values ​​of the internal resistance recorded in the computer memory.

9. Method according to any one of claims 1 to 8, in which the accumulator battery (6) equips a motor vehicle (1) comprising said electric machine (4), the motor vehicle (1) being equipped with a plurality of computers (7, 8, 9), including a first computer (8) configured to control and supervise the inverter, and a second computer (9) configured to control and supervise the battery, the step of generating the current step being implemented by the first computer (8) upon receipt of a control signal from the second computer (9), the step of calculating the internal resistance and the step of estimating the SOHR being implemented by the second computer (9).

10. Electric or hybrid motor vehicle equipped with an accumulator battery (6) and comprising a control system (2) configured to implement the method according to any one of claims 1 to 9.

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