AUTOMOBILE VEHICLE LIMITING CHARGING CURRENT TO PREVENT OVERHEATING AND OVERVOLTAGE, AND TO LITHIUM PLATING, PROCESS AND PROGRAM BASED ON SUCH A VEHICLE

Abstract

The invention relates to a motor vehicle comprising a battery equipped with cells having at least one negative electrode, and a battery controller comprising: - means for measuring the current (MC), voltage (MV), and temperature (MTC) of the cells; - a means for estimating a maximum negative electrode potential (NR) from a model of said potential (NM) as a function of the current (MC) and temperature of the cells (MTC); - a means for estimating the overheating (MTR) of the cells as a function of a temperature threshold; - a means for estimating the overvoltage (VR) of the cells as a function of a voltage threshold; - a means for evaluating a minimum charging current (MIN) corresponding to both the negative electrode potential threshold, the temperature threshold, and the voltage threshold. The invention also relates to a method and a program based on such a vehicle. Figure 2

Description

Title of the invention: MOTOR VEHICLE LIMITING CHARGING CURRENT TO AVOID OVERHEATING AND OVERVOLTAGE, AND LIMITING LITHIUM PLATING, PROCESS AND PROGRAM BASED ON SUCH A VEHICLE

[0001] The invention relates to the field of battery management systems with the objective of diagnosing and controlling a motor vehicle battery.

[0002] The charging capacity of a battery is limited by various factors, and the charging current is defined as described in [Fig. 1]. In this figure, the operations in white boxes represent system operations. Those with dots represent information provided by the equipment supplier.

[0003] The controller is supplied with a CM charging card that limits the charging rate (C-rate – where IC corresponds to the current required to charge a cell for one hour, for example) either based on the state of charge of the cell and the temperature of cells TB1, TBx; or based on the voltage of cells VC1, VCX and the temperature of cells TB1, TBx. This CM charging card generally considers one or more limiting factors (function referenced by "MIN, LV") such as maximum voltage, maximum temperature, and lithium plating generation.

[0004] Reference numerals 1, 2, and X designate different battery cells. VC1 designates the voltage of one of the cells. Reference numerals CCI, CC2, CCX, and CCX-1 designate charging currents. CCM designates a charging current module. LV designates a limiter relative to a maximum voltage VM. LEE designates an electronic limitation based on electronic parameters TE. LCP designates a current I and power P limitation.

[0005] For each cell for which temperature, voltage, and state of charge are available, the CM charging map is interpolated to provide a charging rate (C-rate). The charging rate is multiplied by the corresponding cell capacity.

[0006] The minimum charging current between each cell is then selected. This charging current is then limited by other factors at the module level and at the battery level to calculate the current applied to the cell.

[0007] The current approach has three elements that can be improved: - The cell temperature used to interpolate the CM charging card is based on a bus bar temperature associated with a margin (function M). This method This is not the most accurate approach because a safety margin must be defined. This approach could lead to a loss of performance; - the CM charging board of the cell is only defined by the supplier and uses several limiting factors (voltage, temperature, lithium plating) and assumptions (thermal environment, maximum charging station current, battery architecture) to be built; - The evolution of the CM charging card during aging is based solely on the fact that its capacity decreases, as it provides a charging rate (C-rate) multiplied by the updated capacity. This approach does not guarantee control over the health trajectory to meet the warranty and lifespan objectives.

[0008] An objective of the present invention is to remedy the defects of the prior art, and in particular to improve the efficiency of charge controls and limit premature deteriorations related to lithium plating, overheating or overvoltages.

[0009] To achieve this objective, the invention proposes a motor vehicle comprising a battery equipped with cells having at least one negative electrode, and a battery controller which includes: - at least one means of current measurement measuring a current from the cells; - at least one means of voltage measurement measuring a voltage of the cells; - at least one means of temperature estimation estimating the temperature of the cells; - at least one lithium plating estimation method estimating a potential of said negative electrode from an electrode potential model as a function of current and preferably cell temperature, being below a negative electrode potential threshold; - at least one means of estimating overheating that estimates a maximum cell temperature as a function of a temperature threshold; - at least one means of overvoltage estimation estimating a maximum cell voltage as a function of a voltage threshold; - at least one means of evaluating a minimum charging current corresponding to both the negative electrode potential threshold, the temperature threshold, and the voltage threshold.

[0010] Advantageously, the invention makes it possible to limit the charging current with respect to the estimated negative electrode potential threshold of the cells (to avoid lithium plating), the temperature threshold (to avoid overheating), the voltage threshold (to avoid overvoltage).

[0011] From the user's point of view, the invention makes it possible to reduce charging time and control the health status trajectory (to increase battery life, for example). From the supplier's point of view, the invention provides a generic and adaptive approach to the load controller to reduce development time.

[0012] Preferably, the evaluation means evaluates the minimum charging current corresponding in addition to a maximum power of a charging station or a maximum current of a charging station.

[0013] This allows the use of a minimum charging current, which also preserves the charging station.

[0014] Preferably, the cells further have at least one positive electrode, and the lithium plating estimation means estimates a potential of said positive electrode, and subtracts it from the cell voltage to obtain the potential of the negative electrode.

[0015] This allows the potential of the negative electrode to be evaluated, and therefore the lithium plating, from the potential of the positive electrode.

[0016] Preferably, the motor vehicle includes a means for determining a battery health slope, and said lithium plating estimation means further estimates the negative electrode potential threshold as a function of the battery health slope.

[0017] This allows the negative electrode potential threshold to be calibrated according to an optimized health state trajectory.

[0018] Preferably, the motor vehicle includes a means for measuring the temperature of a coolant, and a means for estimating an open-circuit voltage of the cells, and said overheating estimation means estimates the temperature of the cells from the temperature of the coolant, the voltage, the current and the open-circuit voltage.

[0019] This allows for an accurate estimation of cell temperature from parameters already available in conventional vehicles.

[0020] The invention also relates to a method for controlling the charging current of a motor vehicle according to the invention, comprising the following steps: - at least one current measurement step in which a current from the cells is measured; - at least one voltage measurement step in which cell voltage is measured; - at least one temperature estimation step in which the temperature of the cells is estimated; - at least one lithium plating estimation step in which a potential of said negative electrode is estimated from an electrode potential model in function of the current and preferably the temperature of the cells while being below a negative electrode potential threshold; - at least one overheating estimation step in which a maximum cell temperature is estimated as a function of a temperature threshold; - at least one overvoltage estimation step in which a maximum cell voltage is estimated as a function of a voltage threshold; - at least one evaluation step in which a minimum charging current is evaluated corresponding to both the negative electrode potential threshold, the temperature threshold, and the voltage threshold.

[0021] Preferably, in which, in the evaluation step, the minimum charging current is evaluated, in addition to a maximum power of a charging station or a maximum current of a charging station.

[0022] Preferably, the control method further includes a step of determining a slope of the battery health state, and in the lithium plating estimation step, the negative electrode potential threshold is further estimated as a function of the slope of the battery health state.

[0023] Preferably, the control method further includes a step of measuring the temperature of a coolant, and a step of estimating an open-circuit voltage of the cells, and in the overheating estimation step, the maximum temperature of the cells is estimated from the temperature of the coolant, the voltage, the current and the open-circuit voltage.

[0024] Another object of the invention relates to a computer program comprising program code instructions for executing the steps of the control process according to the invention, when said program is running on a computer.

[0025] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating embodiments of the invention, including: - [Fig.l] schematically illustrates a load control architecture of a motor vehicle according to the prior art; - [Fig.2] schematically illustrates elements of a load control architecture of a motor vehicle according to an embodiment of the invention; - [Fig. 3] schematically illustrates a control architecture according to a first embodiment of the invention; and - [Fig.4] schematically illustrates a control architecture according to a second embodiment of the invention.

[0026] The invention proposes to control the charging current based on the most limiting factors between the estimated negative electrode potential of the cells (to avoid The invention also considers the lithium plating, the internal cell temperature (to prevent overheating and as input for the negative electrode potential estimator), the measured voltage (to prevent overvoltage), and charging station limits. Furthermore, the invention proposes to adjust the margin on the negative electrode potential as a control lever for the health trajectory and charging time. The negative electrode potential can also be deduced by subtracting the positive electrode potential from the cell voltage.

[0027] There are several ways to integrate the invention into the existing solution. As shown in [Fig. 2], the solution consists of the following at the cell level: - a first Brl brick which includes the core temperature estimator TE: it allows to have a precise information of the cell temperature; it includes means of measuring current Mc, coolant temperature MTC, open circuit voltage MOvc, and voltage Mv; - A second component, Br2, concerns a fast charging controller: it calculates the charging current based on all physical limits, including the negative electrode potential; it includes a temperature controller TR with an input of an internal cell temperature TIC (or alternatively a bus bar temperature, a cell wall or tab temperature, or a temperature of a neighboring cell) and an internal temperature request RTC, and an output of an external cell temperature TEC; the external TEC temperature is the input of the NM model as well as the current measured by the Mc means; the output is the value of the negative electrode potential and the internal cell temperature TIC (used by the temperature controller TR); the estimated NEP potential is the input of an NEP potential controller NR as well as an NEP potential request, to determine an allowed CNEP current respecting an NEP potential limit;A temperature regulator MTR receives as input the maximum measured temperature MTmax and a temperature limit LimT and determines an allowed current CTmax respecting a maximum temperature limit LimT; a voltage regulator VR receives as input the cell voltage and a voltage limit and determines an allowed current Cv max respecting a maximum voltage limit; a charging station limiter STR receives as input a power limit Limsip and a current limit LimST c as well as the cell voltage Vceii, and determines an allowed current respecting the power limits LimSTp and current limits LimST c; - A third component, Br3, concerns a health status slope controller, CTSoh-H, which defines the negative electrode potential margin to be considered in the load to influence the health status trajectory. It determines the NEP potential limit used by the NEP NR potential regulator.

[0028] There are several options for integrating the building blocks into the existing solution.

[0029] The second and third bricks can be replaced as illustrated in [Fig.3]. This reduces charging time and controls the health state trajectory.

[0030] The first brick can be replaced as illustrated in [Fig.4]. This allows the charging time to be reduced by providing more information on cell temperatures (in particular a higher thermal degradation current, and a more precise temperature as input data to the charging board).

[0031] The majority of the prior art algorithm can also be replaced by the three building blocks. This makes it possible to combine the two groups of benefits described above.

[0032] The first technical advantage of this invention is that it considers the physical limits of the cell through measurements or estimates instead of a supplier's load chart, which is not fully representative of the application. This makes it possible to reduce charging time while maintaining safe operation.

[0033] The second technical advantage is to use the negative electrode potential limit as a lever to control the trade-off between cell aging and charging time.

[0034] The third advantage is that this approach is generic. For different applications with the same cooling plate and the same cell, only a few simple parameters (number of cells in series and in parallel in the pack) need to be defined to adapt the charge controller to the new application.

[0035] Regarding lithium plating, it is avoided by estimating the potential of the negative electrode NEP and maintaining it above the negative electrode potential limit during charging. The charging current is reduced if the negative electrode potential is too close to its limit.

[0036] In the reference case, the negative electrode potential is derived from an NM model (single-particle model, Newman model, neural network, electrical equivalent circuit model, etc.) with an input current and external cell temperature TEC. The output is the negative electrode potential NEP and the internal cell temperature TIC. The model is initialized with a given initial internal TIC temperature and aging and state-of-charge parameters. The external TEC temperature is regulated so that the internal cell temperature of the negative electrode potential model is equal to the internal temperature derived from the central temperature estimator TR.

[0037] Lithium plating is created more easily at a lower temperature. Therefore, it is proposed to use the minimum internal temperature of the core temperature estimator as the internal temperature.

[0038] Regarding the maximum temperature, the temperature regulation uses an internal temperature estimator whose output is a maximum temperature as very precise information to avoid overheating.

[0039] If the temperature of the cells gets too close to the maximum allowed temperature, the charging current is reduced.

[0040] Regarding the maximum voltage, the voltage regulation uses a cell voltage measurement to avoid overvoltages.

[0041] If this voltage gets too close to the maximum allowed voltage, the charging current is reduced.

[0042] Regarding the maximum performance of the charging station, charging stations are generally limited in current and power. The maximum current and the maximum current reduced by the maximum power are compared, and the lower of the two is the limiting factor.

[0043] To deduce the maximum current from the maximum power, information on the cell voltage can be used, either from the voltage measurement, or from a model or estimator.

[0044] Each of these limiting factors is considered in a minimization function MIN which selects the most limiting factor and applies the corresponding current.

[0045] Brick 3 adds a feedback loop between the health state and the negative electrode potential limit and therefore the charging time.

[0046] To this end, several cell capacity measurements and / or estimates are used to calculate a health trajectory and slope. This trajectory or slope is then compared to a requested trajectory or slope. If the measured trajectory does not match the request, the potential limit is modified.

[0047] For example, if the health state trajectory is faster than the required trajectory to the end-of-life (EOL) health state, the potential limit is increased. This results in an increase in charging time but also a slower transition from the health state to the end-of-life state.

[0048] A health status projection can also be made to predict the health status corresponding to the end of life, and increasing the potential limit of the projection leads to an premature end of life.

[0049] Within the scope of the invention, any regulator can be used.

[0050] A combination of one, several or all of the regulators and limiters may be used.

[0051] Estimation can be used instead of measurement, or vice versa. Measurement can be used instead of the model, or vice versa. The model can be used instead of estimation, or vice versa.

[0052] Additional limitations and regulations may be added to the approach, such as the inclusion of current and thermal limits of bus bars, connectors, power converters or any other equipment between the battery and the charging station.

[0053] This approach can also be adapted for use in energy recovery during driving. In this case, the limitations of charging stations do not apply.

[0054] The health status slope controller is based on the variation of capacity, but can also rely on other methodologies to determine cell aging (e.g., variation of resistance).

[0055] The advantages of this invention include: - a product with better charging performance while retaining the usual components; - to allow control of battery aging, and therefore to delay the slope of battery health status, and increase usage time; - A generic approach to charge control, where recalibration is limited to the component that has changed within the battery. For example, if the cell chemistry is the same, but the battery architecture (x cells in parallel, y cells in series) is different, only one parameter needs to be changed. If the cooler becomes more powerful, the fast-charging controller does not need to be recalibrated.

Claims

Demands

1. A motor vehicle comprising a battery equipped with cells having at least one negative electrode, and a battery controller comprising: - at least one current measurement means (Mc) measuring a current from the cells; - at least one voltage measurement means (Mv) measuring a voltage from the cells; - at least one temperature estimation means (MTC) estimating the temperature of the cells; - at least one lithium plating estimation means estimating a potential of said negative electrode (NR) from an electrode potential model (NM) as a function of the current (Mc), and preferably of the cell temperature (MTC), being less than a negative electrode potential threshold; - at least one overheat estimation means (MTR) estimating a maximum cell temperature as a function of a temperature threshold;- at least one means of overvoltage estimation (VR) estimating a maximum cell voltage as a function of a voltage threshold; - at least one means of evaluating a minimum charging current (MIN) corresponding to both the negative electrode potential threshold, the temperature threshold, and the voltage threshold.

2. Motor vehicle according to claim 1, characterized in that the evaluation means (MIN) evaluates the minimum charging current corresponding further to a maximum power of a charging station (LimSTp) or a maximum current of a charging station (Lim Sic)*

3. Motor vehicle according to any one of claims 1 to 2, wherein the cells further have at least one positive electrode, characterized in that the lithium plating estimation means estimates a potential of said positive electrode, and subtracts it from the cell voltage to obtain the potential of the negative electrode.

4. A motor vehicle according to any one of claims 1 to 3, comprising a means for determining a battery health slope (MSoh), characterized in that said means Lithium plating estimation further estimates the negative electrode potential threshold based on the battery health status slope.

5. Motor vehicle according to any one of claims 1 to 4, comprising a means for measuring the temperature of a coolant (MTC), and a means for estimating an open-circuit voltage of the cells (MOcv), characterized in that said overheating estimation means (MTR) evaluates the maximum temperature of the cells from the temperature of the coolant, the voltage, the current and the open-circuit voltage.

6. A method for controlling the charging current of a motor vehicle according to any one of claims 1 to 5, comprising the following steps: - at least one current measurement step in which a current of the cells is measured; - at least one voltage measurement step in which a voltage of the cells is measured; - at least one temperature estimation step in which the temperature of the cells is estimated; - at least one lithium plating estimation step in which a potential of said negative electrode is estimated from an electrode potential model as a function of the current and preferably the temperature of the cells, being below a negative electrode potential threshold; - at least one overheating estimation step in which a maximum temperature of the cells is estimated as a function of a temperature threshold;- at least one overvoltage estimation step in which a maximum cell voltage is estimated as a function of a voltage threshold; - at least one evaluation step in which a minimum charging current is evaluated corresponding to both the negative electrode potential threshold, the temperature threshold, and the voltage threshold.

7. A control method according to claim 6, wherein in the evaluation step, the minimum charging current corresponding further to a maximum power of a charging station or a maximum current of a charging station is evaluated.

8. A control method according to any one of claims 6 to 7, further comprising a step of determining a battery health slope, characterized in that in the lithium plating estimation step, the negative electrode potential threshold is further estimated as a function of the battery health slope.

9. A control method according to any one of claims 6 to 8, further comprising a step of measuring the temperature of a coolant, and a step of estimating an open-circuit voltage of the cells, characterized in that in the overheating estimation step, the maximum temperature of the cells is estimated from the temperature of the coolant, the voltage, the current and the open-circuit voltage.

10. Computer program comprising program code instructions for performing the steps of the control process according to any one of claims 6 to 9, when said program is running on a computer.

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