Method for estimating the health status of a battery and vehicle adapted to the implementation of this method

Abstract

The invention relates to a method for estimating the health status of electrochemical cells in a battery (6) fitted to a motor vehicle (1) and configured to power an inverter (5) of an electric machine in the motor vehicle. The inverter is driven, in a Park reference frame linked to a rotor of the electric machine, by a direct stator current, a quadratic stator current, and a rotor current. The method comprises: - a step of generating a step of direct stator current from the battery, - a step of determining an internal resistance value, - a step of estimating a value representative of the health status based on the determined internal resistance value. The invention further relates to a motor vehicle configured to implement this method. Figure 1

Description

Title of the invention: Method for estimating the health status of a battery and vehicle adapted to the implementation of this method Technical field of the invention

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

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

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

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

[0005] There are various methods for estimating the health status related to resistance. Some are based on an a priori estimation of the battery's electrochemical evolution, which notably takes into account pre-established durability models, the time spent by the battery in different states of charge, and at different temperatures. These methods have the disadvantage of not allowing the detection of abnormal phenomena that appear with battery aging, 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 when the vehicle is not in operation (in a garage or laboratory), possibly requiring removal of the battery. the battery, and therefore do not allow for on-board operation.

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

[0007] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes a method for estimating SOHR that is accurate and allows for implementation on-board in the vehicle.

[0008] More particularly, the invention proposes a method for estimating a state of health related to the resistance of electrochemical cells in a battery of accumulators configured to power an inverter of an electrical machine, said inverter being driven, in a Park reference 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 generation stage, using the battery, of a current step supplying said inverter, - a step of determining, for at least one electrochemical cell of the accumulator battery, an internal resistance value of the electrochemical cell from a voltage measured across the terminals of the electrochemical cell and the value of the current step, - an estimation step, for said at least one electrochemical cell, of 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 process to be implemented on-board in the vehicle. This eliminates the need for tedious maintenance operations, such as removing the battery. Furthermore, it allows for a greater number of measurements to be taken, thus providing a more precise assessment of the vehicle's condition related to its resistance. In addition, generating 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 features of the process according to the invention, taken individually or in all technically possible combinations, are as follows: - 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 process is implemented upon detection of an activation of a parking mode of the electric motor vehicle or upon detection of a request to start the motor vehicle. - prior to the generation of the current step, the process includes a step of determining a state of charge, the step of estimating the state of health being implemented only for a state of charge within a predetermined range of acceptable values. - the predetermined range of acceptable 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 process includes a step of recording, in a computer memory, the determined value of internal resistance, the step of estimating the state of health related 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 process. - the step of determining the state of health related to resistance involves establishing an average of the determined values ​​of internal resistance recorded in 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 receiving a control signal from the second computer, the step of calculating the internal resistance and the step of estimating the health status related to the resistance being implemented by the second computer.

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

[0012] Of course, the various features, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0013] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0014] On the attached drawings:

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

[0016] [Fig.2] illustrates one method of implementing the process according to the invention;

[0017] [Fig.3] represents, in a first graph, the generation of a current step by the vehicle's accumulator battery 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 the health status related to the resistance of electrochemical cells in a battery pack of an electric or hybrid motor vehicle. Such a motor vehicle, designated by general reference numeral 1 in [Fig. 1], 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 includes in particular an electric machine 4, an inverter 5 and a battery of accumulators 6. The inverter 5 is configured to transform and transmit the electric current supplied by the battery of accumulators 6 to the electric machine 4. It should be noted that the powertrain 3 could optionally include an internal combustion engine and / or another electric machine.

[0020] The electric machine 4 can be of any type (axial or radial flux, wound rotor or permanent magnet...). 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 typically found in motor vehicles or hybrid vehicles, but which are configured here for the implementation of the method according to the invention. Each computer comprises a processor and computer memory, as well as communication interfaces, for example connected to an analog-to-digital converter (ADC) network of the motor vehicle 1. A first computer 7 (commonly referred to by the English term HEVC, for "Hybrid and Electric Vehicle Controller") is configured to monitor the powertrain 3. A second computer 8 (commonly referred to by the English term "Inverter Electronic Control Unit", or "Inverter ECU") is configured to control and monitor 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 storage 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 body of the vehicle. vehicle 1 or, more generally, systems that do not directly concern the powertrain (electric windows, alarms, mirror control, door locks...

[0022] The control of the electric machine 4 is considered here in a Park frame with axes d and q. The Park transform allows the three-phase system of the electric machine 4, classically presented in a fixed frame attached to the stator, to be modeled as a two-phase system in a rotating frame attached to the rotor. Thus, the stator control 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 (classically 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 (classically called the "q-axis") which is perpendicular to the rotor coil. The rotor control is represented by a single rotor current If.

[0023] In this Park frame of reference, 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 pole pairs of the stator.

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

[0027] In a second step E2, upon receiving the control signal, the third computer 9 evaluates the state of charge of the battery 6. Indeed, the inventors observed that when the battery 6 has a low state of charge (SOC), for example, a state of charge below 25% of the maximum charge, then the internal resistance DCR of the cells Electrochemical properties vary greatly with the state of charge. Therefore, the process can be inhibited when the state of charge is below the predetermined threshold (in other words, a state of charge value at least equal to the predetermined threshold is a necessary condition for the process to proceed). If conditions are favorable for the process to continue, for example, if the state of charge is above a predetermined charge threshold, then the process proceeds with a third step E3, which involves the second computer 8 sending a SOHR estimation request to the third computer 9.

[0028] In a fourth step E4, in response to the estimation request, the third computer 9 commands the generation, by the battery 6, of a current step supplying said inverter, here a step of direct stator current 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 to strike a balance between a large step amplitude, which would allow for high accuracy, and a smaller step amplitude, which would reduce current consumption. This balance takes into account, in particular, the maximum operating current of electrochemical cells, which varies depending on the configuration of the motor vehicle and the intended 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 in the battery, from the voltage across 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 involves the detection and acquisition, by the third computer 9, of the current step Id and the voltages across each of the electrochemical cells. For example, the voltage acquisition is carried out after a duration equal to a fraction of the step duration, for example 25%, or after a duration substantially equal to the voltage step duration. 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 battery is given by the following formula

[0032] [Math.2]

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

[0034] Health states related to resistance are then estimated (step E7) based on the calculated internal resistances DCRi and a predetermined value of DCR, referred to as the "beginning of life" value, or DCRbol ("Beginning Of Life" in English), according to the following formula

[0035] [Math.3]

[0036] The internal resistance values ​​DCR and the resistance-related health status 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 calculator 9 calculates a health status related to the overall SOHR resistance of the battery 6 from the SOHR-related health status values ​​stored in the computer memory, for example, by averaging operations. Alternatively, the final step E9 is only implemented if the number of values ​​stored in the computer memory is sufficient to calculate the overall SOHR-related health status. For example, a predetermined number can be defined, which corresponds to a number of previous implementations of the method.

[0038] Thanks to the process described above, in particular thanks to its implementation at the end of each mission, a significant number of measurements are available to improve the accuracy of the health status estimation related to resistance, the SOHR health status 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 a person skilled in the art will be able to make any variant in accordance with the invention.

[0040] For example, an implementation of the method at the end of the vehicle's driving period (end of mission) has been described. According to one embodiment, the method can be implemented after a period of vehicle standstill, for example, when the vehicle is started or when the vehicle doors are unlocked. In this case, in order not to delay the vehicle's start, the duration of the current step can be chosen to be shorter, for example, 500 milliseconds.

[0041] An implementation of the process conditioned on a state of charge of the battery charge level exceeding a predetermined threshold. Alternatively, the process can be implemented regardless of the battery's state of charge, but values ​​measured when the battery's state of charge is below the predetermined threshold are not recorded in the computer memory.

[0042] According to one embodiment, the method according to the invention is implemented after a predetermined delay following a period of vehicle shutdown. In the event of a vehicle shutdown, the control system 9, with the exception of the fourth control unit 10, is switched off. The fourth control unit 10 is then configured to reactivate the control system upon expiration of the predetermined delay in order to initiate the implementation of the method. The initial step 11 therefore involves the fourth control unit 10 sending a wake-up, or power-up, signal to the first control unit 7, which in turn controls the power-up of the other control units 8, 9 of the vehicle 1.

[0043] The inventors observed that the internal resistance value (DCR) increases as the battery temperature decreases. Therefore, according to one embodiment, the measured internal resistance values ​​(DCR) are grouped, at the time of their recording in computer memory, according to the battery temperature, for example, grouped into predetermined temperature ranges (e.g., ranges of three degrees). The health status estimation related to the SOHR resistance can then be performed separately for each temperature or temperature range.

Claims

Demands

1. A method for estimating a state of health (SOHR) related to the resistance of electrochemical cells in a battery (6) configured to power an inverter (5) of an electrical machine (4), said inverter (5) being driven, in a Park frame linked to a rotor of the electrical 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 battery (6), a current step supplying said inverter (5), - a step of determining, for at least one electrochemical cell of the battery (6), an internal resistance value (DCR) of the electrochemical cell from a voltage measured across 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 representative value 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. A method according to claim 1, wherein the current step has a minimum amplitude of 10 amperes.

3. A method according to claim 1 or 2, wherein the accumulator battery (6) is fitted to 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. A method according to claim 3, which is implemented to detect an activation of a parking mode of the electric motor vehicle or to detect a request to start the motor vehicle.

5. A method according to any one of claims 1 to 4, comprising, prior to the generation of the current step, a step (E2) for determining a state of charge of the rechargeable battery (6), the state of health (SOHR) estimation step being implemented only for a state of charge within a range of values predetermined acceptable values.

6. A method according to claim 5, wherein the predetermined range of acceptable 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. A 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 health status related to 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. A method according to claim 7, wherein 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. A method according to any one of claims 1 to 8, wherein the storage battery (6) is fitted to a motor vehicle (1) comprising said electric machine (4), the motor vehicle (1) being fitted 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 a battery of accumulators (6) and comprising a control system (2) configured to implement the method according to any one of claims 1 to 9.

Images