FR3099098A1 - Charging and discharging process of an accumulator battery - Google Patents

Abstract

The invention relates to a method of charging and discharging an accumulator battery (12) of a motor vehicle (10) which is electrically connected to a charging station (20), said method comprising steps: a) receiving data relating to the evolution over time of the electric power for charging and discharging available on the charging station and the associated costs, b) selection of at least a first time slot for charging the battery so that the final charge level is equal to a target charge level, c) selection of at least a second time slot to discharge the battery, d) selection of at least a third time slot to compensate for this discharge, and f ) for charging the accumulator battery. Figure for the abstract: Fig. 1

Description

Method of charging and discharging an accumulator battery

Technical field of the invention

The present invention generally relates to the two-way exchange of electrical energy between a global electrical network and a storage battery, allowing the global electrical network to charge the storage battery or to draw electrical energy from this battery. of accumulators.

It relates more particularly to a method for charging and discharging a motor vehicle storage battery which is electrically connected to a charging terminal, this method comprising steps:
a) receiving data relating to the evolution over time of an electrical charging power available on the charging terminal and of a charging cost,
b) selection of at least a first time slot as a function of the cost of charging and of an electrical charging power for each first time slot selected, so that the final charge level of the storage battery can be, at the end of all the selected time slots, greater than or preferably equal to a target load level, and
f) charging the accumulator battery via the charging terminal during each time slot selected according to the electrical charging power associated with each of these time slots.

It also relates to a motor vehicle equipped so as to be able to implement this method.

State of the art

A hybrid or electric-powered car usually includes a high-capacity storage battery, making it possible to supply current to the electric motors designed to propel the vehicle.

Such a storage battery must be recharged regularly. One solution for this is to electrically connect the car battery to a public charging station.

The ISO 15118 standard was then developed to define a standard communication protocol between a charging station and any car that is likely to connect to it.

To optimize the management of electrical energy, this standard must be used in such a way as to meet various constraints. One of these constraints consists in ensuring that the user has his battery sufficiently charged when he wishes to leave. For this, it is expected that the user defines two first parameters which are, on the one hand, the time at which he wishes to resume his vehicle, and, on the other hand, the level of battery charge desired at this time. -there.

We thus know from the patent document filed under the reference FR1859928 (not yet published on the date of filing of the present document) a method for selecting time slots for charging the battery.

Currently, the electric current used to recharge the batteries of vehicles comes in particular from so-called renewable energies, and in particular from wind energy and solar energy. It turns out that the production of these renewable energies varies a lot depending on the weather conditions. It also turns out that the consumption of electrical energy varies and shows intensity peaks, especially on winter evenings.

A known solution for storing electrical energy in order to be able to restore it at times of peak consumption is then to use the batteries of vehicles connected to the electrical network. This technology, more commonly referred to by its initials V2G (from the English “Vehicle To Grid”), requires the use of reversible chargers and the control of charging and discharging operations by a global monitoring system. This system is indeed necessary to indicate to the charging stations of the electrical network the electrical powers that it can develop or receive at any time of the day.

It then turns out to be necessary to find a time slot selection method which can be implanted in a motor vehicle so as to allow it to communicate with the charging terminal to reserve slots for charging and discharging the storage battery, this method must be simple and quick to implement so as not to slow down the communication protocol between the vehicle and the charging station.

Presentation of the invention

For this, according to the invention, a charging and discharging method as defined in the introduction is proposed, in which, in step a), it is provided to receive data relating to the evolution over time of an electrical discharge power that the storage battery can send back to the charging terminal and a discharge cost, and in which, between steps b) and f), steps are provided:
c) selection of at least one second time slot as a function of the discharge cost and of an electrical discharge power associated with each second time slot selected with a view to discharging the storage battery, and
d) selection of at least a third time slot and of an electrical charging power associated with each third time slot in order to compensate for the discharge of the accumulator battery, so that the final charge level of the accumulator battery can be, at the end of all of the first, second and third time slots selected, greater than or preferably equal to the target charge level.

Thus, thanks to the invention, the vehicle can communicate with the charging terminal so as to reserve first slots for charging its battery, as well as second and third slots to allow the battery to return electrical energy on the global electrical network and then to recharge the battery at other times to compensate for this loss of charge level, the objective remaining to achieve a financial gain by exchanging energy with the electrical network during the second and third slots .

This process is simple to implement and can be implemented very easily in motor vehicle ECUs. It is indeed based on the protocol defined by the ISO 15118 standard, so that it can be deployed easily. It can also be deployed at the level of a global electrical network of any size (district, region, country, etc.).

Other advantageous and non-limiting characteristics of the process in accordance with the invention, taken individually or according to all the technically possible combinations, are the following:
- between steps d) and f), there is provided a step e1) for checking that the charge level of the storage battery remains, during all of the first, second and third time slots selected, greater than a minimum charge level and, if such is not the case, a step e2) of reducing the discharge power of the accumulator battery during said second time slot;
- after step e2), there is provided a step e3) of reducing the charging power during at least the third time slot for which the associated charging cost is the lowest, so as to compensate for the power reduction discharge provided in step e2);
- the accumulator battery being connected to at least one auxiliary device consuming electric current, during steps c) and d), provision is made to neglect the consumption of each auxiliary device and the variation in the temperature of the battery d 'Accumulators ;
- in step e1), the verification is carried out taking into account the consumption of each auxiliary device and the variation in the temperature of the storage battery;
- in step c), the second time slot is distinct from each first time slot and is the one for which the discharge cost is the highest;
- in step d), the number of third time slots is determined so that the sum of the charging powers associated with the third selected time slots is greater than or equal to the sum of the discharge powers associated with the second selected time slots;
- after steps c) and d), provision is made to check that discharging the storage battery is beneficial (relative to the charging and discharging costs) by successively considering each time slot as a second time slot and calculating each time at least one expected profit indicator, the second time slot finally selected being the one for which the expected profit indicator is the greatest, provided that this indicator is positive;
- said expected profit indicator is a function of the difference between, on the one hand, the product of the discharge cost and the discharge power associated with the second slot, and, on the other hand, the product or the sum of the products of the charging cost and charging power associated with each third slot;
- a single third time slot having been selected, said expected benefit indicator is equal to the difference between, on the one hand, the product of the discharge cost associated with the second time slot and the charging power associated with the third time slot, and, d on the other hand, the product of the charging cost and the charging power associated with the third slot;
- it is planned to calculate two expected profit indicators and in which the second time slot finally selected is the one for which the expected profit indicator is the greatest, provided that it is strictly positive;
- During steps c) and d), the selection of the time slots and the electrical power for charging and discharging is carried out according to a charging and discharging cycle efficiency.

The invention also proposes a motor vehicle comprising at least one electric propulsion motor, a storage battery suitable for supplying each electric motor with electric current, a charger suitable for being connected to a charging terminal for charging and discharging the battery of accumulators, and a computer programmed to implement a charging and discharging method as mentioned above.

Of course, the different characteristics, variants and embodiments of the invention can be associated with each other in various combinations insofar as they are not incompatible or exclusive of each other.

Detailed description of the invention

The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

On the attached drawings:

is a schematic view of a vehicle according to the invention, connected to a charging terminal;

are graphs illustrating the temporal variations of powers and costs of a charge and a discharge of an accumulator battery;

are graphs illustrating the temporal variations, discretized by time slots, of the powers and of the charging and discharging costs;

is a flowchart illustrating a first part of a charging and discharging method according to the invention;

is a flowchart illustrating a second part of a charging and discharging method according to the invention;

is a graph illustrating the evolution of the maximum power that the storage battery of the vehicle represented in FIG. 1 can receive as a function of its level of charge, this graph also illustrating the maximum power that the charging terminal can deliver and the maximum power that a motor vehicle charger can receive.

In Figure 1, there is shown a motor vehicle with electric propulsion.

This is a car but it could be another type of motor vehicle (motorcycle, truck, boat, etc.).

This car is here described as electric in the sense that it does not have an internal combustion engine. Alternatively, it could be a plug-in hybrid vehicle.

The electric car 10 conventionally comprises a chassis and wheels. More specifically here it includes:
- at least one electric motor 11 allowing the electric car 10 to move forward,
- an accumulator battery (hereinafter called traction battery 12) connected to each electric motor 11 to supply it with current,
- auxiliary devices 13 consumers of electrical current (air conditioning, multimedia console, etc.),
- a charger 14, and
- a calculator 15.

The charger 14 has a power outlet to which a charging terminal electrical plug 20 can be connected.

This charging terminal 20 is itself connected to a global electrical network.

This electrical network is qualified as global in the sense that it comprises a plurality of charging terminals and in the sense that it is connected to a plurality of current-consuming buildings (homes, offices, factories, etc.) and to a plurality of power sources (wind turbines, electrical panels, electric dam, etc.). It therefore makes it possible to draw electrical energy from current sources to transmit it to buildings and charging stations.

The charging terminal 20 is then designed to deliver an electric current when the traction battery 12 needs to be recharged. It is also provided here to draw an electric current from this traction battery 12 in the event of a peak in consumption on the global electric network, if the conditions allow it.

A regulator is then provided to monitor the overall electrical network and to send messages to the charging terminal 20 in order to inform it of variations in its ability to deliver or draw an electrical current.

At this stage, a charge of the traction battery can be defined as being a phase during which the charging terminal 20 delivers an electric current to the traction battery 12. A discharge will be defined as being a phase during which the charging terminal 20 draws an electric current from the traction battery 12 in order to send it back to the global electrical network.

The charger 14 on board the electric car 10 is connected to the traction battery 12 to charge or discharge it. It is also connected here to the auxiliary devices 13 so as to be able to supply them with current when the electric car 10 is connected to the charging terminal 20.

The computer 15 embedded in the electric car 10 comprises for its part a processor (CPU), a memory and various input and output interfaces.

Thanks to its input and output interfaces, the computer is suitable for receiving input signals from sensors or other devices. It is in particular suitable for receiving the instantaneous charge level SOC ₀ of the traction battery 12.

As shown in Figure 2, it is also adapted to communicate with the charging terminal 20 via the charger 14 to receive data relating to the evolution over time t of:
- the electrical charging power Pc0 available on the charging terminal 20,
- the electrical discharge power Pd0 that the charging terminal 20 can absorb and return to the global electrical network,
- the charging cost Cc0 corresponding to the cost of the electricity available on the charging terminal 20,
- the discharge cost Cd0 corresponding to the resale price of the electricity.

The computer 15 is also adapted to communicate with this same charging terminal 20 to reserve vehicle charging time slots, by selecting an electrical charging power.

Thanks to its memory, the computer 15 stores data used in the context of the method described below.

It stores in particular a computer application, consisting of computer programs comprising instructions whose execution by the processor allows the implementation by the computer 15 of the charging method illustrated in FIGS. 4 and 5 and described below.

This charging process comprises several steps, which can be repeated in a loop.

This process is specially designed to allow the charging of the traction battery 12 by the charging terminal 20 at time slots which assure the user that the traction battery 12 of his electric vehicle 10 will be sufficiently recharged when he has enough. necessary, which make it possible to reduce the cost of this recharging as much as possible, and which possibly also make it possible to resell the electricity stored in the battery in order to make savings (here saving money).

This process is automatically initiated when the electric car 10 is connected to the charging station 20.

The first step EA0 of this process consists in checking that the traction battery 12 is not excessively discharged (which would risk causing premature wear of this battery or which would not allow the user to take his car in an emergency to a predefined route such as the nearest home-to-hospital route).

For this, during this first step EA0, the computer 15 notes the instantaneous charge level SOC ₀ of the traction battery 12. This instantaneous charge level SOC ₀ is here transmitted to the computer 15 by a third-party processor which is in charge of the calculation of this level of charge. As a variant, it could be calculated by the computer 15, according to the voltage at the terminals of the traction battery 12.

The computer 15 then compares this instantaneous charge level SOC ₀ with a predetermined charge level threshold SOCmin recorded in its ROM. This charge level threshold SOCmin is preferably between 10% and 30%. It is here equal to 20%.

If the instantaneous load level SOC ₀ is greater than or equal to the load level threshold SOCmin, the method continues in a step EA1 described below.

Otherwise, the computer 15 sends to the charging terminal 20 a request to recharge the traction battery 12 at the first time slots available, until the instantaneous charge level SOC ₀ reaches the charge level threshold SOCmin . Once this threshold has been reached, the method continues with step EA1.

During the second step EA1, the computer 15 acquires the departure time of the electric vehicle 10, that is to say the time at which the latter should be disconnected from the charging terminal 20.

Here, the computer 15 not only acquires this departure time, but also the target charge level SOC _N that the traction battery 12 must have reached at that time.

For this, the computer 15 can for example ask the user, via a dedicated man-machine interface, the time at which he wishes to leave and the desired place of destination.

Given the desired place of destination, the computer 15 will be able to determine the target charge level SOC _N that the traction battery 12 must have reached to allow the user to reach this place of destination.

As a variant, the computer 15 can automatically determine the time at which the vehicle will leave and the place of destination, for example by detecting that the user systematically uses his electric car 10 to get to work every day of the week.

During step EA1, the computer 15 also receives from the charging terminal 20 data relating to the evolution over time of the electrical charging power Pc0 of the battery available on the charging terminal 20, of the electrical discharge power Pd0 that can be sent back to the global electrical network, the charging cost Cc0 and the discharging cost Cd0.

These costs are expressed here in euros per kWh. Of course, any other currency could be considered. One could also consider considering the costs not financial, but environmental. Any other type of cost could also be considered. The cost considered could alternatively be a compromise between several of the costs mentioned above.

The computer 15 receives for example this data in the form of tables. Such tables are illustrated graphically in Figure 2.

The tables received by the computer 15 here represent these changes up to the time of departure of the vehicle. Alternatively, they could represent these changes over a different period (for example over twenty-four hours if the departure time is not known).

Once received by the computer 15, these tables are here discretized by slots of identical durations Δt (preferably 15 minutes, but here one hour for the sake of simplifying the presentation).

For this, the largest value of the electricity charging cost Cc0 within each slot is used as the unique value of the electricity charging cost Cc during this slot (see figure 3). The smallest value of the electrical load power Pc0 within each slot is moreover used as the only value of electrical load power Pc during this slot. The smallest value of the discharge cost Cd0 of the electricity within each slot is used as the single value of the discharge cost Cd during this slot. The smallest value of the electrical discharge power Pd0 within each slot is moreover used as the only value of the electrical discharge power Pd during this slot. This is the worst case scenario.

The computer 15 then obtains, at each slot T _i :
- the electrical load power Pc _i available,
- the electrical discharge power Pd _i ,
- the cost of charging Cc _i (i.e. the cost of purchasing electricity), and
- the cost of discharging Cd _i (ie the resale price of the electricity).

At this stage, the values of these parameters can be modified so as to take into account the efficiency (less than 1) of the charging and discharging chain.

Each of these values can then be multiplied by the expected return.

Then, if the departure time is more than 24 hours away, the method continues in a step EB1 described below.

Otherwise, the tables are redefined to prevent time slots after this departure time from being selected for charging the traction battery 12 or for discharging it.

For this, the charging cost Cc _i for each time slot after the departure time is set at a very high value, such as for example 10 ¹⁰ euros. In addition or as a variant, the electrical charging power Pc _i for each time slot after the departure time is set to a zero value.

Alternatively, the tables could have been redefined by considering a safety margin of one hour, for example, so as to ensure that the vehicle is loaded one hour before the scheduled departure time.

Once the tables have been redefined, the process continues with step EB1.

This third step EB1 consists in selecting the closest slot T _i to which it will be judicious to charge the traction battery 12.

For this, the computer 15 selects the nearest slot T _i for which the electrical charging power Pc _i is non-zero and for which the charging cost Cc _i is minimum.

During a fourth step EB2, the computer 15 then updates the tables so as to prevent this same time slot T _i from being subsequently re-selected.

To do this, it assigns the value 1 to a charging station occupancy indicator (denoted δ _i ) which is associated with this slot and which is initially at 0.

The following steps will then consist in estimating the level of charge SOC _i+1 that the traction battery 12 should present at the end of the time slot T _i selected, so as to check whether, by charging the traction battery 12 for only this time slot T _i , the user will be able to reach the desired destination.

For this, during a fifth step EC1, the computer 15 estimates the temperature TC _i that the traction battery 12 will present at the time of the selected time slot T _i (the time considered may be the start of the time slot, or even any other time of this slot such as the middle of the time slot).

This temperature TC _i can be estimated from a predetermined mathematical model or from a predetermined map on a test bench.

Here, the computer 15 calculates the temperature Ti using the following mathematical model:

[Math. 1]
MCp.(dTC_I)/dt = RI² + (T_outside- CT_I) / Rthext + (T_air-TC_I) / (Rth(Qm))

Or :
- MCp, R, Rthext and Rth(Qm) are thermal constants depending on the chemistry of the traction battery 12,
- T _ext is the ambient temperature,
- T _air is the temperature of the heating/cooling system of the traction battery 12 if this is activated, and
- I is the current delivered or received by traction battery 12.

The computer 15 then estimates the charge level SOC _i that the traction battery 12 will present at the start of the time slot T _i .

It will be considered here that this level of charge SOC _i will be equal to the instantaneous level of charge SOC ₀ . As a variant, it could be different if provision was made to use the traction battery 12 to supply the auxiliary devices 13 which consume electric current.

During a sixth step ED1, the computer 15 calculates the allowable electrical power Pmax12 by the traction battery 12 during the time slot T _i .

This allowable electrical power Pmax12 is determined as a function of the temperature TC _i and the level of charge SOC _i estimated previously.

As shown by curve C1 in FIG. 6, this power indeed varies according to the SOC charge level of the traction battery 12, and it is all the lower as the SOC charge level is high.

The admissible electrical power Pmax12 also varies according to the temperature of the traction battery 12, this power being all the lower as the temperature T is high.

To determine the admissible electrical power Pmax12, the computer 15 stores in its memory tables of values which make it possible, from the temperature TC _i and the level of charge SOC _i estimated previously, to determine the admissible electrical power Pmax12.

During a seventh step ED2, the computer 15 reads from its memory the maximum admissible electrical power Pmax14 by the charger 12, which is a predetermined constant represented in FIG. 6 by the straight line C2.

It also reads the electrical charging power Pc _i available from the charging terminal 20 at the selected slot T _i , which is represented in FIG. 6 by the straight line C3.

It then selects, among the three powers Pmax12, Pmax14, Pc _i , the one which is the lowest and which therefore forms the link limiting the power at which it will be possible to charge the traction battery 12.

As shown in FIG. 6, this limiting link will not be the same depending on the level of charge SOC of the traction battery 12 (and depending on the temperature of the battery).

The electrical power selected (still denoted for simplification in the rest of this presentation Pc _i ) is then associated with the time slot T _i as being the power which will be requested from the charging terminal 20 to charge the traction battery 12 (and possibly also to power auxiliary devices 13).

The computer 15 then determines the new charge level SOC _i+1 that the accumulator battery 12 will present at the end of the time slot T _i .

The value of this level of charge SOC _i+1 is deduced from the electric power Pc _i which will be debited by the charging terminal 20 during the time slot T _i . It is also deduced from the electrical power consumed by the auxiliary devices 13 (which power will be considered zero below, for simplification).

During an eighth step EE1, the computer 15 begins by determining the electrical energy E _i stored in the traction battery 12 before the selected time slot T _i .

The value of the electrical energy E _i will here be deduced from the instantaneous level of charge SOC ₀ , by means of the following mathematical formula:

[Math. 2]
E _i = SOC ₀ . Emax. SOH/100

Or :
- Emax is a predetermined constant stored in the memory of computer 15, which corresponds to the maximum electrical energy that traction battery 12 can store, and
- SOH is an indicator of the state of health of the traction battery 12, which is transmitted to the computer 15 by a third-party computer.

Then, the computer 15 determines the electrical energy E _i+1 which will be stored in the traction battery 12 at the end of the selected time slot T _i , by means of the following mathematical formula:

[Math. 3]
E _i+1 = E _i + Pc _i .Δt,

with Δt here equal to 60 minutes.

During a ninth step EE2, the computer 15 deduces therefrom the new level of charge SOC _i+1 that the traction battery 12 will present at the end of the selected time slot T _i , by means of the following mathematical formula:

[Math. 4]
SOC _i+1 = 100. E _i+1 / (Emax.SOH)

During a tenth step EF1, the computer 15 compares this new load level SOC _i+1 with the target load level SOC _N .

If the new load level SOCi+1 is greater than or equal to the target load level SOC _N , the method continues in an eleventh step EH1 described below.

Otherwise, that is to say if this time slot T _i will not on its own make it possible to reach the target load level SOC _N , the method is repeated from the third step EB1 so as to verify whether it is possible to sufficiently charge the traction battery 12 by no longer selecting a single time slot, but two time slots.

This process can be repeated as many times as necessary, by selecting as many additional time slots as necessary to reach the target load level SOC _N .

We can then briefly describe the way in which the process repeats itself.

When it repeats the third step EB1 for the first time, the computer 15 selects the nearest new time slot for which the electric charging power Pc is non-zero and for which the electricity charging cost Cc is minimum.

The following steps will then consist in estimating the level of charge that the traction battery 12 should present at the end of the two time slots selected.

To do this, the calculator first considers which of the two time slots selected is closest to the present moment, then it repeats the process with the other time slot, until it finds the battery charge level. of traction at the end of these two slots, which can then be compared with the target load level SOC _N .

Once a sufficient number of time slots has been selected to reach the target load level SOC _N , the method continues in a step EH1 (FIG. 5).

At this stage, the computer 15 knows the value of the occupancy indicators δ_I(equal to 1 only if slot T_Icorresponding has been selected to charge the battery, and equal to 0 otherwise), as well as the value of the energy E_I in the traction battery 12 at the start of each slot.

It is also able to determine the total cost of the load C _ref , by multiplying the electric power of the load Pc _i and the cost of the load Cc _i for each slot T _i selected, and by summing up these products.

To illustrate the invention, the example of FIG. 3 can be taken again, further considering the following hypotheses:
- the electrical energy stored in the traction battery 12 at the time of connection of the latter to the charging terminal 20 is 30 kWh (which can be written E ₀ = 30 kWh),
- the scheduled departure time is in 4 hours,
- the SOCmin charge level threshold corresponds to an energy stored in the battery of 20 kWh, and
- the target load level SOC _N corresponds to an energy of 35 kWh.

In this example, the last slot T ₄ will suffice to reach this target load level SOC _N .

This example can then be illustrated by the following table:

_{T1 T2 T3 T4} Cc _i (Euro/kWh) 2 6 4 1 Pc _i (kW) 3 6 5 5 Cd _i (Euro/kWh) 9 1 7 3 Pd _i (kW) 10 5 4 5 E _i (kWh) 30 30 30 35 δ _i 0 0 0 1

During the aforementioned steps, the computer 15 has selected first time slots T _i to charge the traction battery 12 so that its SOC charge level reaches, at the end of these slots, the target SOC charge level _N.

At this stage, computer 15 will now determine to what extent it will be possible to use traction battery 12 to transfer electrical energy to the global electrical network via charging terminal 20.

It will thus attempt to select one or more second time slots T _i during which the traction battery 12 will discharge onto the global electrical network, and one or more third time slots T _i during which the global electrical network will charge the traction battery 12 in order to compensate for the aforementioned discharge.

For this, for simplification in order to speed up the calculations, the computer 15 will neglect the limitations of the vehicle, the consumption of the auxiliary devices 13 or the temperature variations. This postulate will not have too great an influence on the result of the calculations thanks to the taking into account of the efficiency of a charge/discharge cycle during step EA1.

The objective is then to select the second time slot(s) which are potentially the most profitable for the owner of the vehicle when unloading, and the time slot(s) which are potentially the least costly for the owner of the vehicle when recharging. .

To do this, the computer 15 repeats the following steps EH2 to EH4 in a loop, successively considering all the slots T _i .

During step EH2, the computer thus first of all considers the slot T ₁ . Considering this slot in this way, the computer will test the solution consisting in discharging the traction battery 12 during this slot T ₁ then recharging it during other slots denoted T _j .

For this, it selects all the time slots T _j such that j≠i and δ _j ≠ 1. The computer 15 thus selects all the slots other than the slot T _i considered and which will not be used to charge the traction battery 12.

Among these slots T _j selected, the computer 12 chooses the slot or slots T _j for which the charging cost Cci is the lowest. The objective is to select enough slots T _j so as to compensate for the discharge, which can be written:

It could be an inequality (the sum being greater than or equal to the discharge power Pd _i ). However, as this equation illustrates, the aim is rather to obtain equality, so that it may prove necessary to limit the charging power Pc _j of the last slot T _j chosen.

The computer 15 then calculates two expected benefit indicators making it possible to judge the relevance of using the slot T ₁ to discharge the battery and the slot(s) T _j to compensate for this discharge.

The first indicator, called maximum profit Δmax _i , is calculated at step EH3 using the following equation:

[Math. 6]
, here with i = 1

This maximum profit Δmax _i represents the maximum gain that it is possible to hope for by unloading on slot T _i at maximum power, while recovering on the least expensive available slots the same power under load.

The second indicator, called maximum gain Δlim _i , is calculated at step EH4 using the following equation:

[Math. 7]
, here with i = 1

In this equation, only one slot T _j is considered, namely the one for which the charging power Pc _j is the lowest.

Thus, this maximum gain Δlim _i represents the maximum profit that can be expected by discharging the traction battery 12 on the slot T _i , but by limiting the discharge power Pd _i to the charging power Pc _j of the least available slot. Dear.

These steps can then be illustrated using the example in Figure 3.

The computer 15 first considers the slot T _i =T ₁ .

It then considers first of all that the traction battery 12 discharges on this slot T ₁ at maximum power (ie 10 kW), then it determines the slot T _{j which} is the least expensive to charge. This is slot T ₃ . The electrical charging power Pc _j available on this slot is only 5 kW.

This power not being sufficient to compensate for the discharge, the computer selects a second pulse T _j . This is the slot T ₂ . The electrical load power Pc _j available on this slot is 6 kW. Only 5kW will be needed to compensate for the 10kW discharge.

The calculator can thus calculate the maximum profit Δmax _i , here equal to 40.

Considering only slot T3, for which the charging cost is the lowest, the computer can also calculate the maximum gain Δlim _i , which here is equal to 25.

It will be noted that if the calculation of these two indicators is impossible, for example because there are not enough slots available to be able to compensate for the discharge of the traction battery 12, the value 0 is assigned to these two indicators .

The computer 15 then repeats these operations considering that the slot T _i is successively the time slot T ₂ then the time slot T ₃ .

The computer 15 also repeats these operations by considering the slots T _i having already been selected during the steps EB1 (for which the occupancy indicators δ _i are equal to 1). However, in this case, it takes into account the loss of load which would result from the deselection of such a slot.

All of these calculations then make it possible to complete the first table in a second table:

_{T1 T2 T3 T4} Cc _i (Euro/kWh) 2 6 4 1 Pc _i (kW) 3 6 5 5 Cd _i (Euro/kWh) 9 1 7 3 Pd _i (kW) 10 5 4 5 _δi 0 0 0 1 Δmax _i 40 -9 16 -23 Δlim _i 25 -3 15 -17

A negative value of an expected benefit indicator reveals that it would be financially disadvantageous to discharge the traction battery during the corresponding slot T _i .

Thus, in step EH5, if all the expected profit indicators Δmax _i , Δlim _i are less than or equal to 0, the computer 15 does not reserve any slot to discharge the traction battery 12.

Otherwise, the process continues in a step EH6 during which the computer selects the expected profit indicator whose value is the greatest. In the example considered here, it is the maximum profit Δmax ₁ .

Consequently, the computer 15 plans to select the slot T ₁ to discharge the traction battery 12, then the slots T ₂ and T ₃ to compensate for this discharge by recharging the battery at a power of 5 kW.

It will be noted that if the maximum gain Δlim ₁ had been the greatest, the computer would have planned to select the pulse T ₁ to discharge the traction battery 12 to a power of 5 kW, then the pulse T ₃ to compensate for this discharge by recharging the battery with a power of 5 kW.

Be that as it may, during step EH7, the computer then updates the occupancy indicators δ _i by fixing their values to 1 for the charging slots and to -1 for the discharging slots.

It also updates the electrical energy value E _i stored in the battery at each slot, by means of the following equations.

If a new discharge is planned during the slot T _i , this electrical energy E _i will be calculated using the equation:

[Math. 8]
E_I =E_i-1-P_I .Δt

If a new load is planned during the slot T _i , this electrical energy E _i will be calculated using the equation:

[Math. 9]
E_I =E_i-1+ P_I .Δt

If a discharge is planned during the slot T _i while a load was initially planned there, this electrical energy E _i will be calculated using the equation:

[Math. 10]
E_I =E_i-1-P_I .Δt - Pc_I .Δt

Finally, for the time slots T _i that have not been selected either to charge or to discharge the traction battery 12, we can write:

[Math. 11]
E_I =E_i-1

Note that if we update the energy E_Iof time slot T_I, it will also be necessary to update the energies of the time slots T_mfollowing (with m>i). For example, in the case where the energy E_Ion each slot is initially at 30 kWh (which can be written E₁=E₂=E₃=E₄= 30kWh), and where the traction battery 12 is charged on the time slot T₁of 5kWh, then we will have to update the energy E2 as well as the energies of the other time slots that follow (which we can write E₁= 30kWh and E₂=E₃=E₄= 35 kWh).

In the example considered here, we can then complete Table 1 as follows:

_{T1 T2 T3 T4} Cc _i (Euro/kWh) 2 6 4 1 Pc _i (kW) 3 6 5 5 Cd _i (Euro/kWh) 9 1 7 3 Pd _i (kW) 10 5 4 5 E _i (kWh) 20 25 30 35 _δi -1 1 1 1 P _i (kW) 10 5 5 5

In this table, the power P _i corresponds to the power used to charge or discharge the traction battery 12 during the slot T _i considered.

These steps EH1 to EH7 are then repeated in a loop, so as to be able to select other charging and discharging slots, until all the indicators Δmax _i , Δlim _i are less than or equal to 0 or until that all the occupancy indicators δ _i are non-zero.

When this is the case, a new step EG1 is provided for verifying that the SOC charge level of the battery will at all times be greater than or equal to the minimum charge level SOCmin, so as to ensure the user good availability of his vehicle even if he had to interrupt the charging and discharging cycle undertaken.

During this step, the computer begins by calculating the minimum electrical energy E _min corresponding to this minimum charge level SOCmin, using the following equation:

[Math. 12]
Emin = SOCmin. Emax

Then, the computer checks that for each slot T _i , the energy E _i is greater than or equal to the minimum electrical energy E _min .

If such is the case, the computer continues the process in a last step EG3 described below.

Otherwise, if for at least one slot T _i , the energy E _i is strictly less than the minimum electrical energy E _min , the computer 15 calculates the excess energy ΔE discharged too much to respect the condition of not -exceeding the minimum load level SOCmin, using the equation:

[Math. 13]
ΔE = Emin - _Ei

The computer will then ensure that this excess energy ΔE is canceled by reducing the discharge power during the less financially profitable slot(s).

Of course, the least profitable slot must be selected from among the time slots which precede the time slot T _i on which the load level SOC is lower than the minimum load level SOCmin.

More precisely, the computer selects slot T _i :
- during which it was planned to discharge the traction battery (which is written δ _i = -1),
- which has the lowest discharge cost Cd _i , and
- which precedes the time slot on which the SOC load level is lower than the minimum load level SOCmin.

Two cases are then possible.

The first case is that where the electrical energy taken from the traction battery 12 during this slot is greater than the excess energy ΔE (which can be written P _j ≥ ΔE / Δt). In this case, the modification in power drawn off during this slot alone will suffice to cancel out the excess energy ΔE. Then, the computer reduces the discharge power during this pulse T _i by means of the following equation:

[Math. 14]
P _{j, new} = P _{j , old} - ∆E / ∆t

Then, the computer continues the process in a step EG2 described below.

The second case is that where the electrical energy taken from the traction battery 12 during this time slot T _i is less than the surplus energy ΔE, so that the modification of power taken during this single slot T _i will not suffice to cancel the excess energy ΔE.

Consequently, the computer 15 calculates a new excess energy value ΔE by means of the following equation:

[Math. 15]
ΔE_new = ΔE_ancient–P_I. ∆t

Then, it deselects the slot T _i , by canceling the power P _i and the occupancy indicator δ _i .

It also updates the electrical energies at the end of each slot using the following equation:

[Math. 16]
E_I =E_d-1 + P_I. ∆t

Step EG1 is then repeated in a loop until the excess energy ΔE is canceled.

At this stage, the reduction in the discharge of the traction battery 12 during one or more time slots so as to comply with the condition relating to the minimum charge level SOCmin is such that the computer must accordingly reduce the charge of the battery so as not to unnecessarily exceed the SOC _N target charge level at the scheduled departure time.

To compensate for this reduction in discharge, the computer will modify the charging cycles accordingly, during step EG2.

For this, the computer 15 successively considers all the slots T _k for which it was planned to charge the battery (that is to say for which the occupancy indicator δ _k is equal to 1) and which follow the slot during which the planned charging power has been reduced (k therefore ranging from i+1 to N).

The computer will then select the slot T _k for which the charging cost Cc _k is the highest, then it will reduce the charging power used during at least this slot, proceeding substantially in the same way as above.

More specifically, the computer 15 determines an energy difference ΔE' between the electrical energy desired at the end of the process (corresponding to the target charge level SOC _N ) and the electrical energy which would be obtained at the end of the process by following the discharge and discharge cycles expected at this stage.

It should be noted here that one could consider that the energy difference ΔE' is equal to the excess energy ΔE.

So, two cases are then possible.

The first case is that where the electrical load energy during the selected pulse T _k is greater than the energy difference ΔE' (which can be written P _k ≥ ∆E' / ∆t). In this case, the change in charging power during this single pulse T _k will suffice to cancel the energy difference ΔE′. Then, the computer reduces the load power during this pulse T _k by means of the following equation:

[Math. 17]
P _{k , new} = P _{k , old} - ∆E' / ∆t

Then, the computer continues the process in a last step EG3 described below.

The second case is that where the electrical charging energy during this pulse T _k is less than the energy difference ΔE', so that the modification of the battery charging power during this single pulse does not will not suffice to cancel the energy difference ΔE'.

Consequently, the computer 15 calculates the new value of the energy difference ΔE' by means of the following equation:

[Math. 18]
ΔE'_new = ΔE'_ancient–P_k. ∆t

Then, it deselects the slot T _k , by canceling the power P _k and the occupancy indicator δ _k .

It also updates the electrical energies at the end of each slot using the following equation:

[Math. 19]
E_k =E_{k -1} –P_k. ∆t

These operations are repeated until the energy difference ΔE' is canceled.

The last step EG3 implemented by the computer 15 is a step of simulating the charging and discharging session.

To take into account the limitations induced by the traction battery 12 used and by any changes in temperature, the computer 15 checks one last time that all the values selected make it possible to comply with the conditions relating to the minimum charge level SOCmin and to the level target load SOC _N .

If not, steps EG1 and EG2 are repeated.

Otherwise, the computer 15 is then able to quickly send the charging terminal 20 a request in which are the reserved time slots and the electrical power requested or offered at each time slot.

This method is based on a simplified estimation of the evolution of the SOC charge level of the traction battery 12, in order to reduce the computing power necessary to implement the method.

It may then happen that the estimate is slightly erroneous.

To avoid any charging or discharging problem, once the session has started, it is preferably provided to implement an operation for monitoring the evolution of the SOC charge level of the traction battery 12.

For this, the computer records at each instant the instantaneous value of the SOC charge level of the traction battery 12, then it compares this value with that which was expected.

As long as the difference between these two values remains below a predetermined threshold, no correction is undertaken.

On the other hand, if this difference exceeds the threshold, the computer 15 reinitializes the method described above, in particular by sending a request to the charging terminal to find out the new tables of cost of electricity and power available from the thick headed.

When implementing the method, a correction coefficient is however applied here, for example to the calculation of the allowable electrical power Pmax12 by the traction battery 12.

The value of this correction coefficient is preferably adjusted as a function of the speed with which the instantaneous value of the charge level has deviated from the expected value of the charge level.

Once the process is complete, the computer 15 sends a new request to the charging terminal 20 to reserve new time slots: this is referred to as “re-negotiation”.

The present invention is in no way limited to the embodiments described and represented, but those skilled in the art will know how to make any variant in accordance with the invention.

Claims (12)

Method for charging and discharging an accumulator battery (12) of a motor vehicle (10) which is electrically connected to a charging terminal (20), said method comprising steps:
a) receiving data relating to the evolution over time of an electrical charging power (Pc) available on the charging terminal (20) and of a charging cost (Cc),
b) selection of at least a first time slot (T _i ) as a function of the charging cost (Cc) and of an electrical charging power (Pc _i ) for each first time slot (T _i ) selected, so so that the final charge level of the accumulator battery (12) can be, at the end of all the time slots (T _i ) selected, greater than or preferably equal to a target charge level (SOC _N ), and
f) charging the storage battery (12) via the charging terminal (20) during each time slot (T _i ) at said associated electrical charging power (Pc _i ),
characterized in that, in step a), provision is made to receive data relating to the evolution over time of an electrical discharge power (Pd) that the accumulator battery (12) can send back to the charging terminal (20) and a discharge cost (Cd), and in that, between steps b) and f), steps are provided:
c) selection of at least one second time slot (T _i ) as a function of the discharge cost (Cd) and of an electrical discharge power (Pd _i ) associated with each second time slot (T _i ) selected with a view to discharge the storage battery (12), and
d) selection of at least a third time slot (T _i ) and of an electrical charging power (Pc _i ) associated with each third time slot (T _i ) with a view to compensating for the discharge of the storage battery (12), so that the final charge level of the storage battery (12) can be, at the end of all the first, second and third time slots (T _i ) selected, higher or preferably equal to the target charge level (SOCN). Charging and discharging method according to the preceding claim, in which, between steps d) and f), there is provided a step e1) of checking that the level of charge (SOC) of the accumulator battery (12) remains, during all of the first, second and third time slots (T _i ) selected, greater than a minimum load level (SOCmin) and, if such is not the case, a power reduction step e2) discharge (Pd _i ) of the accumulator battery (12) during said at least one second time slot (T _i ). Charging and discharging method according to the preceding claim, in which, after step e2), there is provided a step e3) of reducing the charging power (Pc _i ) during the third time slot (T _i ) for which the associated charging cost (Cc _i ) is the lowest, so as to compensate for the reduction in discharge power (Pd _i ) provided for in step e2). Charging and discharging method according to one of the two preceding claims, in which the accumulator battery (12) being connected to at least one auxiliary device (13) consuming electric current, during steps c) and d), provision is made to neglect the consumption of each auxiliary device (13) and the temperature variation (TC) of the accumulator battery (12), and in which, in step e1), the verification is carried out by taking account of the consumption of each auxiliary device (13) and of the temperature variation (TC) of the accumulator battery (12). Charging and discharging method according to one of the preceding claims, in which, in step c), the second time slot (T _i ) is distinct from each first time slot (T _i ) and is the one for which the cost of discharge (Cd _i ) is the highest. Charging and discharging method according to one of the preceding claims, in which, in step d), the number of third time slots (T _i ) is determined so that the sum of the charging powers (Pc _i ) associated with the third time slots (T _i ) selected is greater than or equal to the sum of the discharge powers (Pd _i ) associated with the second time slots (T _i ) selected. Charging and discharging method according to one of the preceding claims, in which, during steps c) and d), it is provided to check that the discharging of the accumulator battery (12) is beneficial by successively considering each pulse time slot (T _i ) as the second time slot (T _i ) and each time calculating at least one expected profit indicator (Δmax _i , Δlim _i ), the second time slot (T _i ) finally selected being the one for which the expected profit indicator (Δmax _i , Δlim _i ) is the largest, provided that this expected profit indicator (Δmax _i , Δlim _i ) is strictly positive. Charging and discharging method according to the preceding claim, in which said expected profit indicator (Δmax _i ) is a function of the difference between, on the one hand, the product of the cost of discharging (Cd _i ) and the discharging power ( Pd _i ) associated with the second slot (T _i ), and, on the other hand, the product or the sum of the products of the charging cost (Cc _i ) and the charging power (Pc _i ) associated with each third slot ( T _i ). Charging and discharging method according to the preceding claim, in which, a single third slot (T _i ) having been selected, said expected profit indicator (Δlim _i ) is equal to the difference between, on the one hand, the product of the cost discharge (Cd _i ) associated with the second slot and the charging power (Pc _i ) associated with the third slot, and, on the other hand, the product of the charging cost (Cc _i ) and the charging power (Pc _i ) associated with the third slot (T _i ). Charging and discharging method according to the two preceding claims, in which provision is made to calculate two expected profit indicators (Δmax _i , Δlim _i ) and in which the second time slot (T _i ) finally selected being that for which the indicator of expected profit (Δmax _i , Δlim _i ) is the greatest, provided that this indicator of expected profit (Δmax _i , Δlim _i ) is strictly positive. Charging and discharging method according to one of the preceding claims, in which, during steps c) and d), the selection of the time slots (T _i ) and the electric power of charge (Pc _i ) and discharge (Pd _i ) is performed based on a charge and discharge cycle efficiency. Motor vehicle (10) comprising at least one electric motor (11) for propulsion, an accumulator battery (12) adapted to supply electric current to each electric motor (11) and a charger (14) adapted to be connected to a charging unit (20) for charging and discharging the accumulator battery (12), characterized in that it comprises a computer (15) programmed to implement a charging and discharging method in accordance with one of the preceding claims.