Method of determining the target charging current of a high-voltage battery of an electric vehicle based on a target state of charge and a target charging time set by a user

Abstract

A method (50) of determining the target charging current (ITarget) of a high-voltage battery of an electric vehicle based on a target state of charge (SOCTgt) and a target charging time (Δtusr) is described. The electrical power (PHV_load) absorbed by the active electrical loads during the charge phase, the initial state of charge (SOCAct), and the temperature (TBatt) of the battery are detected by means of vehicle sensors. A first value of charging current (IOpt) is determined (502), based on the electrical power and the electrical resistance of the battery, which minimizes the energy loss due to the active electrical loads and thermal dissipation. A second value of constant charging current is determined (504), based on the battery capacity, the target charging time, the target state of charge, and the initial state of charge, that, if maintained for the target charging time, allows the target state of charge to be reached. A curve indicative of the limit values of the charging current based on the state of charge is determined based on the initial state of charge and the temperature of the battery. If the second current value exceeds the limit values: (i) the duration of a first charging phase during which the second current value is lower than the limit and the duration of a second charging phase during which the second current value is higher than the limit are determined; (ii) a limit state of charge reachable within the first charging phase is determined based on the second current value and the temperature of the battery; and (iii) a third value of constant charging current (In+1) is determined (504) based on the nominal capacity, the target charging time, the target state of charge, the initial state of charge and the limit state of charge that, if maintained during the first charging phase, and if during the second charging phase the charging current tracks the limit curve, allows to reach the target state of charge. It is selected (506), as the target charging current, the maximum between the first current value and the second current value if the second current value does not exceed the limit curve, and the maximum between the first current value and the third current value if the second current value exceeds the limit curve.

Description

[0001] “Method of determining the target charging current of a high-voltage battery of an electric vehicle based on a target state of charge and a target charging time set by a user”

[0002] ****

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the invention

[0005] The present invention relates to electric vehicles equipped with a high-voltage battery, for example an 800 V battery, which supplies energy mainly to the electric powertrain (for this reason also called “traction battery”), and which can be charged by connecting to an external charging infrastructure (so-called charging “columns”). Such vehicles may include battery electric vehicles (BEVs) or hybrid electric vehicles (HEVs).

[0006] The invention was developed with reference to the determination of an optimal value of the charging current (i.e. , the current absorbed by the high-voltage battery) during the so-called “scheduled charging” phases, i.e., charging phases in which the user can set the desired start and end times of charging (from which a desired charging time can be derived, e.g., 8 hours) and a desired target state of charge at the end of charging (e.g., 97% of the total capacity of the high-voltage battery).

[0007] Prior art

[0008] Some modern electric vehicles, in which there is a high-voltage battery (e.g., 800 V - also referred to as “HV battery” in the present disclosure, from the English “High-Voltage”) dedicated primarily to powering the powertrain and other relevant electrical loads (e.g., the air conditioning system of the passenger compartment, the heating and / or cooling system of the battery pack, etc.), allow the user to choose between various charging modes, including the so-called “scheduled charging”. When selecting the scheduled charging mode, the user can set the start and end times of charging and the target State Of Charge (SOC) that he / she wishes to achieve at the end of the scheduled charging operation (e.g., 97%, etc.).

[0009] In conventional solutions, during the execution of a scheduled charging, no particular algorithms are applied to determine the value of the charging current. For example, the vehicle can absorb the maximum current that can be supplied by the charging column, in order to ensure that the state of charge desired by the user is reached within the imposed charging time. This approach, however, is not particularly efficient, because the absorption of an unnecessarily high (or, at the opposite end, excessively low) charging current determines energy losses and inefficiencies, so that the charging operation is carried out in a suboptimal manner.

[0010] Document US 2023 / 0336003 A1 is exemplary of the prior art, and discloses a battery charging management system and method for a battery pack with a plurality of communication-enabled chargeable battery units. The system includes a charging management base configured to transmit charging setting information for the battery units, a plurality of user terminals configured to transmit user preset information related to battery charging, a respective charging control unit in each of the battery units, and a communication connection for transferring data between the charging management base at one end and the battery units at the other end and between the user terminals at one end and the charging management base and / or battery units at the other end. The charging setting information and / or user preset information includes charging mode information related to a plurality of different charging modes for the battery units. The charging setting information and / or user preset information may be transmitted to the charging control unit of the respective battery unit via the communication connection. The respective charging control unit is configured to carry out a charging process of its battery unit coupled to a charger, to define information about the desired value of the associated charging parameters based on the supplied charging setting information and / or user preset information and to communicate this to the charger. If necessary and depending on the application, the user preset information may in particular also contain information useful for various aspects of scheduled charging, whereby the user can make presets for the charging control unit regarding when he / she wants to have a certain battery unit of the battery pack available, and with which state of charge. Such targeted presets may include, for example, information on a desired battery unit or a desired battery type, a desired usage time, a desired purpose of use, i.e. in which work appliance the battery unit is intended to be used, a desired battery voltage and / or a desired amount of energy. The charging setting information may also contain other preset information, in addition to the plain charging mode information, such as the set of an optimal state of charge for relatively long storage of the respective battery unit, and / or the preset of a priority charging mode, such as the gentle charging mode that is optimal for the lifetime of the battery unit or the sustainable charging mode that is optimal with regard to environmental aspects. The charging control unit then determines the optimal charging process in each case for the respective battery unit taking these preset objectives into account.

[0011] Document US 11101677 B2 discloses methods and systems for charging exchangeable energy storage devices positioned in a device exchange station. The method includes: receiving demand information; determining a charging plan for the device swap station at least partially based on a state of charge of each of the exchangeable energy storage devices located in the device swap station, information on demand and the available power of the device swap station; generating a charging command for each of the exchangeable energy storage devices based on the charging rule for each of the exchangeable energy storage devices; and transmitting the charging commands to the device swap station.

[0012] Document US 6979977 B2 discloses a power controller for a vehicle that controls the power supply to an electrical load when the vehicle engine is stopped or the key switch is turned off, so as to prevent the reduction of the residual capacity of the main battery. The control system has a control part that controls the operation of a power generator and an electrical load mounted on an automotive vehicle. The control system also includes residual capacity measuring means for measuring the residual capacity of a battery. The control part operates a predetermined electrical load when the engine is stopped or when a key switch is kept off, and operation of the electrical load is stopped when the residual capacity of the battery measured by the residual capacity measuring means becomes less than a specified value.

[0013] Other documents potentially of interest in the field of the invention are JP 2023-076555 A, US 8922329 B2, and US 9318917 B2.

[0014] Therefore, there is a need in the art to develop a method of determining an optimal value of the charging current of the high-voltage battery in an electric vehicle during a scheduled charging operation, in order to increase the overall efficiency of the charging itself.

[0015] Object of the invention

[0016] The object of the invention is to solve the above-mentioned technical problem. In particular, the object of the invention is to provide a method of determining, based on a charging time and a target state of charge set by a user (i.e., during a scheduled charging operation), an optimal value of the charging current that allows to meet the requests set by the user and at the same time increase (e.g., maximize) the efficiency of the charging process.

[0017] Summary of the invention

[0018] The object of the invention is achieved by a method having the features forming the subject of the following claims, which form an integral part of the technical teaching provided herein in relation to the invention.

[0019] The method may be implemented by one or more electronic control units of a vehicle, for example a control unit of the battery management system (BMS).

[0020] Brief description of the figures

[0021] The invention will now be described with reference to the attached figures, provided purely by way of non-limiting example, in which:

[0022] - Figure 1 is a diagram illustrating the trend of the energy dissipated during the charging of a high-voltage battery of an electric vehicle, based on the charging current;

[0023] - Figure 2 is a diagram illustrating the trend of the limit charging current based on the time elapsed during the charging of the high-voltage battery of an electric vehicle;

[0024] - Figure 3 is a diagram illustrating the trend of the limit charging current based on the state of charge of the high-voltage battery during the charging of the high-voltage battery of an electric vehicle;

[0025] - Figure 4 is a graph illustrating the trend of the limit state of charge of the high-voltage battery based on the charging current, in particular the trend of the limit state of charge which, once reached, no longer allows a constant charging current to be maintained as a limit charging current is reached, for different temperature values of the high-voltage battery; - Figure 5 is a block diagram exemplary of the steps of a process of determining an optimal charging current of a high-voltage battery of an electric vehicle during a scheduled charging phase, according to one or more embodiments of the present disclosure;

[0026] - Figure 6 is a block diagram exemplary of some implementation details of the method illustrated in Figure 5, according to one or more embodiments of the present disclosure; and

[0027] - Figure 7 is a graph illustrating the trend of the limit charging current based on the state of charge of the high-voltage battery for different temperature values of the high-voltage battery.

[0028] Detailed description

[0029] As mentioned, the invention applies to electric vehicles equipped with a high-voltage battery that can be charged via a charging infrastructure external to the vehicle (charging column), and which allow the user to perform so-called “scheduled charges” in which the user can set the initial and final times of the charging (from which a desired charging time can be inferred) and a desired target state of charge (SOC) at the end of the charging. Under these conditions, the object of the present invention is to determine an optimal value of the battery charging current that allows to increase the efficiency of the charging, reducing the dissipated energy (due to the Joule effect and due to the electrical loads of the vehicle that are kept active during the charging) compared to known solutions.

[0030] When charging the high-voltage battery of an electric vehicle, a part of the energy taken from the charging infrastructure (column) is dissipated during the charge itself, rather than being stored in the battery. The efficiency of the charging process can therefore be defined as the ratio between the energy that is actually transferred to the battery and the total energy that is supplied by the column. There are mainly two dissipation factors. The first factor is due to the hourly energy consumption of all the electrical and electronic components of the vehicle that must be powered during charging, i.e. , mainly the DC / DC converter that supplies energy to the low-voltage systems (e.g., electronic control units) that must be powered and functioning to manage the charging process. The second dissipation factor is due to the Joule effect (thermal dissipation), the extent of which depends substantially on the electrical resistance of the high-voltage battery.

[0031] Therefore, the total energy dissipated during a charging process (ELOSS) can be computed according to the following equation 1 which includes two main terms: where HR is the power dissipated by the battery due to the Joule effect (from the English Heat Rejection), Pnvjoad is the power dissipated by the vehicle electrical loads that are active during charging (e.g., the DC / DC converter that powers the low-voltage systems, including the control unit BMS), At is the duration of the charging, R is the electrical resistance of the high-voltage battery, and I is the charging current to the battery, which is assumed to be constant (the expression HR = Rl2is nothing but the law of the Joule effect, for which the thermal dissipation is equal to the product of the resistance of the electrical conductor by the square of the current flowing through it).

[0032] Furthermore, the duration of the charging At (e.g., expressed in hours) can be determined based on the total (nominal) capacitance Cnom of the high-voltage battery (e.g., expressed in Ampere-hours, Ah), the charging current I (e.g., expressed in Ampere, A), which is again assumed to be constant, and the difference ASOC between the target state of charge SOCrgt set by the user and the initial state of charge SOCAct at the start time of charging (dimensionless), according to the following equation 2:

[0033] Substituting this equation into the previous one gives the following equation 3 which allows to express the total energy ELOSS dissipated during a charging process based on the (constant) charging current / :

[0034] As can also be seen from the diagram of Figure 1 , the trend of the dissipated energy ELOSS as a function of the charging current I is controlled:

[0035] - for low values of the current / , by a term inversely proportional to the current / , since the charging times become longer and therefore the constant hourly loads Pnvjoad become predominant; and - for high values of the current / , by a term directly proportional to the current / , since the dissipation due to the Joule effect becomes predominant.

[0036] Therefore, by decreasing the value of the charging current / , the energy dissipated thermally due to the Joule effect is reduced but the energy dissipated over time by the electrical loads is increased (for the simple fact that constant electrical loads will have to be powered for longer), while increasing the value of the charging current I reduces the energy dissipated over time by the electrical loads (reducing the overall charging time) but the energy dissipated thermally due to the Joule effect is increased. It follows that the dissipated energy ELOSS has a minimum point ELossjviin in correspondence of an optimal value loPt of the charging current / , as illustrated in the diagram of Figure 1 . By deriving the previous equation 3 with respect to the charging current I and computing the point where the derivative is zero, the following equation 4 is obtained which determines the value of the optimal current loPt >

[0037] This (constant) value of optimal current loPt, however, does not take into account the user needs imposed with the scheduled charge, i.e. , it does not ensure that the achievement of a certain target state of charge SOCrgt is met within the time limit set by the user. Therefore, it is also appropriate to compute a minimum current value that must be maintained so that the scheduled charge is completed within the time interval set by the user (indicated by Atusr in the present disclosure), possibly also taking into account a time safety margin (indicated by Atsafety in the present disclosure) to be sure that the charging is actually completed within the time limit set by the user. The actual charging time can therefore be indicated by At’usr = Atusr - Atsafety. For example, if the time Atusr (determined by the user by setting the start and end times of the charging) is equal to 8 hours (480 minutes), the safety interval Atsafety (automatically determined by the vehicle) could be equal to 15 minutes or 30 minutes, and the actual charging time At ’usr could be equal to 465 or 450 minutes.

[0038] A first value In of the minimum (constant) charging current can be computed using equation 2 again (inverting it) and imposing that the considered time interval At is equal to the actual charging time At’usr, according to the following equation 5:

[0039] On the other hand, the computation of the minimum current In according to equation 5 does not take into account the fact that, as the battery charging progresses (and therefore as time passes and the battery charge level increases), the effective charging current is progressively limited to an increasingly smaller value, in order to comply with a certain limit current curve imposed (for safety reasons) by the battery supplier. This condition is illustrated in the diagram of Figure 2, where the current value In is indicated and the curve representing the trend of the limit charging current lum based on the time elapsed from the initial charging time tstart is indicated. As can be observed, it is possible that, before reaching the end of the charging (i.e., before the end of the time interval At ’usr which occurs at the time tend — tstart + At’ usr = tstart + Atusr - Atsafety), the current In intersects the curve lum (at the time tcross) and therefore, in the last charging phase indicated by ECP (End Charge Phase) and having a duration indicated by Atn, the effective charging current is limited to a value lower than In. It follows that, by carrying out the charging at a constant current value equal to In, the amount of charge approximated by the triangle Q1 illustrated in Figure 2 (assuming that lum has a decreasing linear trend in the final time interval Atn) may not be transferred to the vehicle battery within the time expected by the user, and therefore the state of charge at the end of the scheduled charging may be lower than that requested by the user.

[0040] It is therefore appropriate to compute more precisely (at least) another value ln+i of the minimum (constant) charging current, which is slightly higher than In and which substantially allows the transfer of the quantity of charge corresponding to the triangle Q1 in the time interval between the start of charging (tstart) and the time tcross in which the charging current would be limited. This value of the current ln+i is also indicated in the diagram of Figure 2: it will be noted that the area of the rectangle Q2, which indicates the surplus of charge that the current ln+i allows to transfer with respect to the current In in the time interval between tstart and tcross, is substantially equal to the area of the triangle Q1. The difference between the current ln+i and the current In is indicated by Al. Using a minimum charging current of ln+i ensures that all the energy needed to charge the battery up to the state of charge required by the user is transferred within the maximum time set by the user (i.e. within the time tend), and at the same time ensures that the current limit lum set by the battery cell supplier is not exceeded. In particular, charging is performed at a constant current of ln+i between tstart and tcross, and with a current that decreases over time

[0041] (approximately linearly) following the trend of the limit curve lum in the time interval Atn between tcross and tend. The average current in the time interval Atn can therefore be approximated with the value ln / 2.

[0042] The condition described above is also illustrated in the diagram of Figure 3, where the current value In is indicated and the curve of the limit charging current lum is indicated based on the state of charge SOC of the battery. Here, SOCAct indicates the initial state of charge of the battery, SOCrgt indicates the final state of charge set by the user, S0Cum,n indicates the state of charge reached at the time tcross if charging is performed with a constant current equal to In, and C1 indicates the remaining capacity of the battery that is charged at a limited current to reach the target state of charge SOCrgt.

[0043] The following equation 6 expresses the value of the current ln+i

[0044] In+1= In+ I (6)

[0045] The equation 6 can therefore be rewritten as follows (equation 7): where Cnom is the nominal capacity of the battery and Atn is the duration of the charging phase ECP (between tcross and tend), whose value is given by the following equation 8:

[0046] Considering the combination of equations 7 and 8, it can be observed that the determination of the value of the current ln+i can be carried out starting from the values of the parameters S0Cum,n, SOCAct, SOCrgt, Cnom, Atusr and Atsafety. The parameters Atusr and SOCrgt are input parameters in the method according to the present disclosure, as they are set by the user as target parameters of the programmed charge. The parameter SOCAct is also an input parameter, as it is detected by a sensor of the state of charge of the high-voltage battery. The value of the parameter Cnom is stored internally by a vehicle control unit, and the value of the parameter Atsafety is either stored or computed internally by a vehicle control unit (e.g., it can be fixed or vary based on the charging time Atusr). The value of the parameter SOCum,n can instead be determined by a vehicle control unit based on the current In (and therefore, in turn, based on SOCAct, SOCrgt, Cnom, Atusr and Atsafety see equation 5) and based on the high-voltage battery temperature TBatt (detected by a dedicated temperature sensor), using one or more stored characteristic maps (e.g., implemented by analytical or piecewise functions, or look-up table), which are usually provided by the battery cell supplier or manufacturer. The dependence of the limit state of charge SOCum,n (i.e., the state of charge that can be reached before a current limitation occurs, charging the battery with the constant current In) on the current In and the temperature TBatt is qualitatively represented by graph 40 of Figure 4, which illustrates the trend of S0Cum,n as a function of In for different values of TBatt, specifically for four different values Tsatti, TBatt2, Tsatts, Tsatt4. Generally, the state of charge S0Cum,n increases as the temperature TBatt increases. Therefore, in the example of Figure 4, we could have TBatti>TBatt2>TBatt3>TBatt4. Furthermore, generally the state of charge S0Cum,n decreases as the current In increases.

[0047] It will be understood that the method for computing the charging current ln+i described herein can be repeated iteratively, starting each time from the previously computed value, to increase the precision of the value of target charging current (thus, computing subsequent values ln+2, ln+3, etc. using the same approach).

[0048] Therefore, the method according to this invention can be schematized by the block diagram of Figure 5. In particular, method 50 comprises a step 502 in which the value of the optimal charging current loPt is computed using the equation 4 presented above, based on the current power Pnvjoad absorbed by the active electrical loads of the vehicle (measured by one or more vehicle sensors) and based on the electrical resistance R of the high-voltage battery (not indicated as an input parameter at block 502, as it is a value that can be stored in a vehicle control unit). Method 50 also includes a step 504 in which the value of the charging current ln+i is computed, using the equations 7, 8 and 5 presented previously, based on the input parameters SOCrgt and Atusr set by the user, and the detected parameters SOCAct and TBatt. Method 50 also includes a step 506 in which the values loPt and ln+i are received as input and additional boundary conditions are considered, as further described below, to determine the final value / Target of the charging current to be used during the scheduled charging phase.

[0049] Further details of method 50 can be described by referring to the block diagram of Figure 6. In block 602, the nominal capacity Cnom is multiplied by the ASOC requested by the user (i.e. , SOCrgt - SOCAct), and in block 604 this product is divided by the actual charging time At ’usr or, in other words, Atusr - Atsafety, thus obtaining the current value In at the output of block 604. In block 606, the current value In is compared with the limit curve lum. if In exceeds the curve lum, a control signal of a selector 608 is asserted, while if In does not exceed the curve lum, the control signal of the selector 608 remains deasserted. The curve lum can be determined by a vehicle control unit based on the initial state of charge SOCAct (detected by a respective sensor) and based on the temperature TBatt of the high-voltage battery (detected by a dedicated temperature sensor), using one or more stored characteristic maps (e.g., implemented by analytical or piecewise functions, or look-up table), which are usually provided by the supplier or manufacturer of the battery cells. The dependence of the limit current lum on the state of charge SOCAct and the temperature TBatt is qualitatively represented by graph 70 of Figure 7, which illustrates the trend of lum based on SOCAct for different values of TBatt, specifically for four different values TBatti, TBatt2, TBatt3, TBatt4. Typically, the limit current lum increases with increasing temperature TBatt up to a threshold temperature (e.g., around 50°C), while once the threshold temperature is exceeded the limit current lum decreases with increasing temperature TBatt to implement thermal protection of the battery component. Thus, in the example in Figure 7, one could have TBatt3<TBatti<TBatt2<TBatt4, with TBatt3 and TBatti less than the threshold temperature and Tsatt2 and Tsatt4 greater than the threshold temperature. Additionally, typically the limit current lum decreases with increasing state of charge SOCAct.

[0050] The selector 608 outputs the current value ln+i if In > lum, and outputs the current value In otherwise. In a block 610, the maximum value is selected amongst the value provided by the selector 608 and the optimal current value lopt (already computed), outputting a raw target current value lTarget_Raw. At this point, it is possible to carry out further checks of certain boundary conditions, to determine the final target current value / Target. In particular, in block 612, the real-time value of the state of charge (during charging) SOC is compared with a minimum critical SOC value SOCMin, i.e. , a value that ensures that the vehicle can be moved in emergency situations for a certain distance (e.g., SOCiviin can be equal to 30% or 20%). If the realtime state of charge SOC is lower than the critical value SOCiviin, a control signal of a selector 614 is asserted, while if the real-time state of charge SOC is higher than the critical value SOCiviin the control signal of the selector 608 remains deasserted. The selector 614 outputs the minimum value between lum and IchargerMax (determined by block 616) if SOC < SOCiviin, and outputs the current value lTarget_Raw otherwise. In particular, the current IchargerMax is the maximum current that the charging infrastructure can supply. Essentially, therefore, the selector 614 allows the following logic to be followed in real time during charging:

[0051] - if the current state of charge SOC is lower than the critical value SOCMin, the battery is charged with the highest possible current, while preserving both the operating limits of the battery (i.e., lum) and the operating limits of the charging station (i.e. , IchargerMax), to the detriment of losses due to the Joule effect, but thus ensuring that, in the event of disconnection from the charging station earlier than expected, the vehicle has been charged as much as possible to reach the “minimum” safety charge level;

[0052] - if the current state of charge SOC has exceeded the critical value SOCMin, then the charging logic switches to an operation based on maximum efficiency, charging the battery with a constant current equal to / rarge Raw determined as previously discussed.

[0053] In a block 618 the current value output from the selector 614 is then limited to zero at the lower end and to the minimum value between lum and IchargerMax at the upper end to produce the final target current value / Target while ensuring compliance with the operating limits of the vehicle and the external charging infrastructure.

[0054] The method of determining the optimal charging current described herein thus allows for increasing the efficiency of scheduled charging, improving the charging performance of the vehicle and reducing energy losses, and at the same time preserving the operating limits of both the vehicle (in particular, the high-voltage battery) and the charging infrastructure.

[0055] Of course, the details of construction and the embodiments may be widely varied with respect to what is described and illustrated without thereby departing from the scope of the invention as defined by the attached claims.

Claims

CLAIMS1. A method (50) of determining a target charging current ( / Target) of a high-voltage battery of an electric vehicle based on a target state of charge (SOCrgt) of the high-voltage battery and a target charging time (Atusr) set by a user, said method (50) comprising:- sensing, via one or more sensors of said vehicle, the electrical power (Pnvjoad) absorbed by the electrical loads of said vehicle that are active during said charging phase, the initial state of charge (SOCAct) of the high-voltage battery, and the temperature (Tsaff) of the high-voltage battery;- determining (502), based on said electrical power (Pnvjoad) and a stored resistance value of said high-voltage battery, a first value of charging current (loPt) that minimizes the energy loss (ELOSS) due to said active electrical loads and to the thermal dissipation of said high-voltage battery;- determining (504; 602, 604), based on a stored nominal capacity value (Cnom) of said high-voltage battery, on the target charging time (Atusr), on the target state of charge (SOCrgt), and on the initial state of charge (SOCAct), a second value of constant charging current (In) that, if maintained for said target charging time (Atusr), allows to reach said target state of charge (SOCrgt)’,- determining (70), based on the initial state of charge (SOCAct) and on the temperature (TBatt) of the high-voltage battery, a curve indicative of limit values of the charging current (lum) as a function of the state of charge;- if said second value of charging current (In) exceeds said curve indicative of limit values of the charging current (lum)(i) determining the duration of a first charging phase during which said second value of charging current (In) is lower than said limit curve (lum), and the duration (Atn) of a second charging phase during which said second value of charging current (In) is higher than said limit curve (lum),(ii) determining (40), based on the second value of charging current (In) and on the temperature (TBatt) of the high-voltage battery, a limit state of charge (S0Cum,n) reachable within said first charge phase, and(iii) determining (504), based on the nominal capacity value(Cnom) of said high-voltage battery, on the target charging time (Atusr), on the target state of charge (SOCrgt), on the initial state of charge (SOCAct) and on the limit state of charge (SOCum,n), a third value of constant charging current (ln+i) that, if maintained during said first charge phase, and if during said second charging phase the charging current tracks said limit curve (lum), allows to reach said target state of charge (SOCrgt) and- selecting (506, 610), as target charging current (Irarget), the maximum value amongst said first value of charging current (loPt) and said second value of charging current (In) if said second value of charging current (In) does not exceed said limit curve (lum), or the maximum value amongst said first value of charging current (loPt) and said third value of charging current (ln+i) if said second value of charging current (in) exceeds said limit curve (lum).

2. The method (50) of claim 1 , wherein said first value of charging current (loPt) is determined (502) computing the square root of the ratio between said electrical power (Pnvjoad) and said stored resistance value of said high-voltage battery.

3. The method (50) of any of the previous claims, wherein said second value of constant charging current (In) is determined (504; 602, 604) multiplying the nominal capacity value (Cnom) by the difference between the target state of charge (SOCrgt) and the initial state of charge (SOCAct), and dividing said product by the target charging time (Atusr).

4. The method (50) of any of the previous claims, wherein said third value of constant charging current (ln+i) is determined (504) carrying out the following operations:- adding up the difference between the limit state of charge (S0Cum,n) and the initial state of charge (SOCAct), and half of the difference between the target state of charge (SOCrgt) and the limit state of charge (S0Cum,n)- multiplying said sum by the nominal capacity (Cnom) of said high- voltage battery; and- dividing said product by the difference between the target charging time (Atusr) and the duration (Atn) of the second charge phase.

5. The method (50) of any of the previous claims, wherein the duration (Atn) of the second charging phase is determined multiplying thenominal capacity value ( Cnom) by the difference between the target state of charge (SOCrgt) and the limit state of charge (SOCum,n), and dividing said product by said second value of charging current (In).

6. The method (50) of any of the previous claims, comprising setting (612, 614, 616) the value of said target charging current (Irarget) equal to the minimum value selected amongst a current limit value of the charging current determined via said limit curve (lum) and a maximum current value (IchargerMax) that can be provided by the charging infrastructure, as long as the current value of the state of charge (SOC) of the high-voltage battery is lower than a minimum threshold value ( SOC / vnn) of the state of charge.

7. The method (50) of any of the previous claims, comprising limiting (618) the value of said target charging current (Irarget) to zero at the lower end and to the minimum value selected amongst a current limit value of the charging current determined via said limit curve (lum) and a maximum current value (IchargerMax) that can be provided by the charging infrastructure at the upper end.

8. The method (50) of any of the previous claims, wherein said target charging time (Atusr) is reduced by a certain time safety margin (Atsafety) to determine an actual charging time (At’usr), and wherein said actual charging time (At’usr) is used in the place of said target charging time (Atusr) to determine (504; 602, 604) said second value of charging current (In) and said third value of charging current (ln+i).

9. The method (50) of claim 8, wherein said time safety margin (Atsafety) is determined based on the target charging time (Atusr) set by the user.

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