Single battery-powered motor vehicle

Abstract

The invention relates to a device such as, for example, a motor vehicle (1) comprising an on-board electrical system (40), at least one electric motor (20) for propelling the motor vehicle, and a battery (10). According to the invention, the battery (10) of this device comprises a casing (13) that houses first battery cells (11) and second battery cells (12) adapted to be electrically isolated from the first battery cells. From this casing emerge first connection terminals for the first battery cells to the on-board electrical system and second connection terminals for the second battery cells to the electric motor. A DC-DC converter (30) is provided, connected on one side to the second connection terminals and, on the other side, to the on-board electrical system, and controlled by a computer. Figure for the abstract: Fig. 1

Description

Title of the invention: Single-battery motor vehicle Technical field of the invention

[0001] The present invention relates generally to the management of electrical energy in a motor vehicle.

[0002] It relates more particularly to a device such as a motor vehicle, comprising two electrical networks operating at distinct voltages, and a battery of accumulators.

[0003] It also relates to a method for controlling this device. State of the art

[0004] Electric or hybrid motor vehicles are generally equipped with two batteries.

[0005] A first battery, called a traction battery, is mainly dedicated to the traction of the vehicle.

[0006] Generally, such a traction battery is of the high-voltage lithium-ion type (its electrolyte comprising a lithium salt solution). The capacity of such a battery is generally between 20 and 100 kWh.

[0007] A second battery, known as the accessory battery, is primarily dedicated to supplying power to the vehicle's onboard electrical system (computers and low-consumption electrical devices such as heating elements, fans, actuators, sensors, etc.). Thanks to its high level of reliability, it ensures the power supply to essential vehicle systems such as the braking and steering systems. Furthermore, it is capable of providing electrical power during extended periods of vehicle inactivity.

[0008] Generally, such an accessory battery is a lead-acid type (the anode is usually made of lead while the cathode is made of lead dioxide). The capacity of such a battery is generally between 20 and 60 Ah (which corresponds to only a few hundred Wh).

[0009] This second battery suffers from various drawbacks.

[0010] In particular, it is heavy and bulky, and has a limited lifespan (around 3 to 4 years).

[0011] Moreover, following new standards aimed at limiting the use of lead, it will soon no longer be possible to use it. It will then have to be replaced by lead-free accessory batteries (for example, lithium-ion), which suffer from other problems, notably cost. Presentation of the invention

[0012] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes to combine the two batteries into one single battery, without however merging them completely.

[0013] Indeed, the solution of using a single battery to power a load such as an electric motor and the on-board network would not be sufficiently safe, particularly in the event of failure while driving or during prolonged parking of the vehicle.

[0014] Therefore, according to the invention, a device is proposed comprising: - a first electrical network operating at a first voltage, - a second electrical network operating at a second voltage higher than the first voltage, - a battery of rechargeable batteries, and - a charger suitable for charging the rechargeable battery and operating on one of the first and second voltages, the battery of accumulators comprising a casing which houses first battery cells and second battery cells adapted to be electrically isolated from the first battery cells, and from which emerge first connection terminals of the first battery cells to the first electrical network and second connection terminals of the second battery cells to the second electrical network, and - a DC-DC converter which is connected, on one side, to the second connection terminals, and, on the other, to the first electrical network and which is controlled by a computer.

[0015] Preferably, the device is formed by a motor vehicle, in which case the first electrical network is an on-board electrical network and the second electrical network includes at least one load here formed by an electric propulsion motor of the motor vehicle.

[0016] Thus, thanks to the invention, the housing contains cells which may be identical but which are not all connected together, some being dedicated to the high voltage supply of the electric motor while others are dedicated to the low voltage supply of the on-board network.

[0017] This structure has many advantages. It offers the benefits of using a single battery without suffering from the associated disadvantages.

[0018] For example, all cells can benefit from the same performance without needing to multiply the devices for providing this performance. Thus, all cells can be managed by the same battery management system (BMS), they can be heated or cooled by the same circuit...

[0019] In addition, it is possible to use the same first and second battery cells, which facilitates the manufacture of the battery and reduces its cost given the large volume of cells purchased.

[0020] Finally, connecting the DC-DC converter from the second battery cells to the on-board electrical network, which is also powered by the first battery cells, allows the operating point of this converter to be adjusted so that it has optimal efficiency.

[0021] This architecture more generally allows DC-DC converters to be used optimally in various configurations, as will be described below.

[0022] Preferably, the housing contains a single battery management system that is adapted to communicate with the first and second battery cells.

[0023] Advantageously, the housing contains at least one first switch which is interposed between one of the first terminals and the first electrical network, and at least one second switch which is interposed between one of the second terminals and a load of the second electrical network (for example the motor), the first and second switches being controlled by the battery management system and / or by the computer.

[0024] Advantageously, the housing accommodates a cooling and / or heating circuit adapted to cool and / or heat the first and second battery cells.

[0025] Preferably, the first and second battery cells are all identical.

[0026] The invention also proposes a method for controlling a DC-DC converter of a device such as the one mentioned above, according to which it is provided to characterize an operating point of the device and to control the DC-DC converter as a function of the operating point between: - a direct state in which the current from the second battery cells powers at least the first electrical network, and - an inverted state in which the current from the first battery cells powers at least the load of the second electrical network.

[0027] Other advantageous and non-limiting features of the process according to the invention, taken individually or in all technically possible combinations, are as follows: - the DC-DC converter can be controlled, depending on the operating point, in a stopped state in which the second battery cells are electrically isolated from the first battery cells and the first electrical network; - when the load is powered by the second battery cells, it is planned to determine a charge level of the first battery cells, then at least if the measured charge level exceeds a first threshold, to control the DC-DC converter in reverse state, preferably at a current that maximizes the efficiency of the DC-DC converter; - when the electric motor is powered by the second battery cells, it is planned to determine a charge level of the first battery cells, then at least if the measured charge level exceeds a first threshold, to drive the DC-DC converter in reverse state (preferably at an intensity maximizing the efficiency of the DC-DC converter); - when the load of the second electrical network is supplied with current by the second battery cells, it is planned to determine a charge level of the first battery cells, then, at least if the measured charge level is below a second threshold, to drive the DC-DC converter in direct state so that the second battery cells supply the first electrical network and recharge the first battery cells at an intensity maximizing the efficiency of the DC-DC converter; - if the measured charge level is above the second threshold, the DC-DC converter is planned to be driven in reverse state; - when the load is supplied with current by the second battery cells, it is planned to determine the intensity of the current consumed by the first electrical network, then, at least if the measured intensity is less than a third threshold, to control the DC-DC converter in the stopped state so that only the first battery cells supply the first electrical network; - when the load is stopped, it is planned to control the DC-DC converter in a stopped state so that only the first battery cells power the first electrical network; - when the electric motor is stopped, it is planned to control the DC-DC converter in a stopped state so that only the first battery cells power the first electrical network; - when the battery is connected to an external charging network (via the charger), it is planned to start by driving the DC-DC converter in the off state so that only the first battery cells supply the first electrical network and only the second battery cells charge, then, before the second battery cells are fully charged, to drive the DC-DC converter in the forward state so that the first and second battery cells charge, the current through the DC-DC converter preferably being maintained at a value maximizing the efficiency of the DC-DC converter (the first cells preferably charging at a current maximizing the efficiency of the DC-DC converter).

[0028] Of course, the various features, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0029] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0030] On the attached drawings:

[0031] [Fig-1] is a schematic view of a motor vehicle according to the invention;

[0032] [Fig.2] is a homologous view of that of [Fig.1], illustrating the vehicle in a first load configuration;

[0033] [Fig.3] is a homologous view of that of [Fig.1], illustrating the vehicle in a second rolling configuration;

[0034] [Fig.4] is a homologous view of that of [Fig.1], illustrating the vehicle in a third rolling configuration;

[0035] [Fig.5] is a homologous view of that of [Fig.1], illustrating the vehicle in a fourth rolling configuration;

[0036] [Fig.6] is a homologous view of that of [Fig.1], illustrating the vehicle in a fifth rolling configuration;

[0037] [Fig.7] is a homologous view of that of [Fig.1], illustrating the vehicle in a sixth parking configuration;

[0038] [Fig.8] illustrates three graphs, an upper graph representing the evolution over time of the charge of the second battery cells of the motor vehicle of [Fig.1], an intermediate graph representing the evolution over time of the power delivered by the DC-DC converter of this motor vehicle, a lower graph representing the evolution over time of the charge of the first battery cells of this motor vehicle.

[0039] In [Fig.1], a motor vehicle 1 is shown.

[0040] It could be any type of vehicle, for example a truck, a bus, a boat, an airplane...

[0041] This is a car classically comprising a chassis, four wheels, a powertrain, a steering system and a braking line.

[0042] These different elements being well known, they will not be described here in detail.

[0043] It can only be specified that the powertrain can be either hybrid or purely electric. In all cases, it will include a battery 10 and at least one electric motor 20. It will also preferably include a charger 21 for recharging the battery 10.

[0044] The electric motor 20 may be of any type (axial or radial flux). It shall include an inverter section for converting direct current into alternating current, and at least one drive section.

[0045] The charger 21 may also be presented in various forms. In practice, it will comprise a housing adapted to be connected to an external electrical network 100, and electrical components enabling the housing to be connected to the battery 10. This connection may be made directly, if the external electrical network 100 delivers a direct voltage, or via an AC-DC converter if the external electrical network 100 delivers an alternating voltage.

[0046] The electric motor 20 forms a high-voltage component of the vehicle, in that it is designed to operate at high voltages, at least above 40V and typically 400 or 800V.

[0047] The vehicle may include other high-voltage components, such as a heating and / or air conditioning system.

[0048] All of these high-voltage components are connected within a high-voltage network.

[0049] The motor vehicle also includes an on-board network 40 separate from this high-voltage network.

[0050] The on-board network 40 is defined here as comprising all the vehicle equipment which must be supplied at a reduced voltage, at least less than 60 V and here in the order of 12 to 14 V. It is therefore a low voltage network.

[0051] As illustrated in the figures, this on-board network 40 includes at its input a current interruption device 41 such as a terminal fuse box. It also includes, connected to the output of this current interruption device 41, equipment 42 such as actuators, sensors, controllers...

[0052] The vehicle also includes a computer 50, which here forms one of the components of the on-board network 40, although for clarity in the figures it is shown separately. This computer 50 includes a processor, memory, and a data exchange interface, connected, for example, to a CAN network of the vehicle.

[0053] Thanks to this interface, the computer is adapted to receive various pieces of information characterizing a point of operation of the vehicle, for example the status of the charger 21 connected or not to the external electrical network 100, data from the accumulator battery 10...

[0054] Thanks to this interface also, the computer is adapted to control various electrical components, as will become clear in the rest of this presentation.

[0055] Thanks to its memory, the calculator 50 stores a computer application, consisting of computer programs including instructions whose execution by the processor allows the implementation by the calculator of the process described below.

[0056] The accumulator battery 10 is preferably unique, in the sense that no other battery comprising electrochemical cells is provided in the vehicle.

[0057] Consequently, this single battery 10 is intended to supply: - the on-board electrical network 40 at a first electrical voltage, and - the vehicle's high voltage network, in particular the electric motor(s) 20, at a second electrical voltage higher than the first electrical voltage.

[0058] This battery of accumulators 10 comprises for this purpose a single hermetically sealed case 13.

[0059] This housing 13 accommodates two types of electrochemical battery cells (hereafter simply referred to as cells).

[0060] The cell(s) 11 of the first type (hereafter referred to as first cells 11) are preferably all identical.

[0061] The cells 12 of the second type (hereafter referred to as second cells 12) are preferably all identical.

[0062] The first cells 11 and the second cells 12 are preferably still all identical, which will allow economies of scale to be achieved during the manufacture of the battery.

[0063] Thus, these cells 11,12 are distinguished into two “types” not necessarily according to their intrinsic characteristics, but in the sense that they are connected in such a way as to form two distinct sets of cells, which can be electrically isolated from each other.

[0064] These cells are typically of the lithium-ion type. For example, they have a voltage across their terminals of around 3 to 4 V and an individual capacity of around 100 Wh.

[0065] The first cells 11 are more specifically designed to supply the low-voltage on-board network 40. They are therefore fewer in number here compared to the second cells 12. There are four of them here.

[0066] They are designed to operate between two charge level limits, namely between a lower threshold SOCmin (for example, 8%) and an upper threshold SOCmax (for example, 95%). The lower threshold SOCmin is specifically designed so that the vehicle can remain parked for a significant period even when the secondary cells are discharged. The objective is that, after such a period, the charge level SOC11 of these primary cells 11 remains above a minimum safety threshold SOCsaf.

[0067] If there are two or more of them, these first cells 11 are connected (at least in part) in series between first connection terminals 18 emerging from the housing 13. It will be noted here that one of these first two terminals 18 is connected to ground while the other is connected to the current cutting device 41, via a controlled switch 15 (made up of relays or MOSFETs) housed in the housing 13.

[0068] The second cells 12 are more specifically designed to supply the high-voltage network, and therefore in particular the electric motor 20, at a high voltage. They are connected (at least partially) in series between second connection terminals 19 emerging from the housing 13. It should be noted here that these two second terminals 19 are connected to the high-voltage network (here to the electric motor 20 and the charger 21), via two controlled switches 16 housed in the housing 13.

[0069] These second cells are for example about 100 or 200 in number depending on the voltage required by the high voltage network (400 or 800V).

[0070] Preferably, the housing 13 also houses a battery management system 14, commonly called a BMS, which is preferably a single unit connected to the first and second cells 11, 12 and to the controlled switches 15, 16. In another embodiment, the battery management system may be located remotely and outside the housing 13. In this alternative embodiment, it may be connected to the first and second cells by wire, or by a wireless connection typically of the Bluetooth® type. Communication is established between these components in any case.

[0071] As is known, such a battery management system 14 includes a processor and allows for monitoring, controlling, and balancing the voltages of the cells in the rechargeable battery 10 in order to maximize its performance, safety, and lifespan. Here, this battery management system 14 is unique in that it allows for balancing the voltages of the first cells 11 and balancing the voltages of the second cells 12 independently. Indeed, the first cells may have different voltages than the second cells (some being more discharged than others). This battery management system 14 is therefore adapted to control the controlled switches 15, 16.

[0072] The housing 13 also contains a cooling system which may take on very diverse forms. Preferably, this cooling system will be designed to cool the first and second cells 11, 12 with similar efficiency (within 50%).

[0073] The motor vehicle also includes a DC-DC converter 30 having two input terminals connected to the two second terminals 19 of the accumulator battery 10, and two output terminals connected to the on-board network 40. In practice, one of these output terminals is connected to the first cells 11 while the other is connected to the current cut-off device 41. The objective is that the current emitted by these output terminals can power the on-board network 40 and the first cells 11.

[0074] This DC-DC converter 30 could be of standard type, in that it could inject current only in a direct direction (from the second cells 12 to the on-board network 40 and / or the first cells 11).

[0075] However, this DC-DC converter 30 is preferably reversible, in that it can be controlled between: - a direct state in which it injects current from the second cells 12, for example so that these cells supply the on-board network 40 and / or the first cells 11, - an inverted state in which it injects current from the first cells 11, for example so that these cells power the electric motor 20 and / or the second cells 12.

[0076] Thus, it will be able to implement all the configurations described below. If it were of the standard type, it would of course only be able to implement some of these configurations.

[0077] Preferably, the DC-DC converter 30 can also be controlled in a stopped state in which no current flows through it, so that the second battery cells 12 are electrically isolated from the first battery cells 11 and the on-board network 40.

[0078] It should be noted here that the efficiency of this DC-DC converter 30 depends on the current flowing through it. Generally, as this current increases from 0 A to a maximum threshold, its efficiency varies according to a bell-shaped curve: it increases very rapidly up to a first current (here 25 A), then more slowly up to a maximum, and then decreases slowly. In other words, there is an optimal current iopt at which the efficiency of the DC-DC converter 30 is maximum. While it is preferable to use this converter at this optimal current iopt, it is in any case preferable not to use it below the first current.

[0079] The computer 50 is intended to communicate with the battery management system 14 and with this DC-DC converter 30 to implement the different configurations described below, depending on the operating point of the vehicle.

[0080] It should be noted here that the "operating point" is defined by parameters characterizing the state of the vehicle, such as the charge level of the first and / or second battery cells, and / or the current consumption level by the high-voltage network, and whether or not the charger 21 is connected to the external electrical network. 100, the position of a powertrain control lever in "parking" mode or not...

[0081] The configurations are described as non-limiting examples, to illustrate how the motor vehicle can be used and in particular how the DC-DC converter 30 can be controlled by the computer 50.

[0082] A first configuration is illustrated in [Fig.2].

[0083] In this first configuration, it is assumed that the user has connected the charger 21 to the external electrical network 100 and has requested the charging of the accumulator battery 10.

[0084] We observe on [Fig.2] that the charger 21 is connected in such a way as to be able to directly charge the second cells 12.

[0085] Charging the first cells 11 is not required. However, it is preferably carried out via the DC-DC converter 30.

[0086] Indeed, as will be explained below, it will be preferable to charge these first cells since, when their charge level SOC11 is sufficiently high, they will not only be able to power the on-board network 40 but also participate in the power supply of the electric motor 20 during driving or other high voltage components (if any) when the vehicle is awake but not moving.

[0087] In this charging configuration, the computer 50 then controls the controlled switches 15, 16 in the closed state and the DC-DC converter 30 in direct mode, so that the current from the second cells 12 and / or the charger 21 powers the on-board network 40 and also recharges the first cells 11.

[0088] The charging of these batteries is interrupted when their charge level SOC11 exceeds a predetermined charge threshold, for example the upper threshold SOCmax. For this purpose, the controlled switch 15 can be activated to open or, preferably, the DC-DC converter 30 is controlled to supply the current consumed by the on-board network 40.

[0089] A second configuration is illustrated in [Fig.3].

[0090] In this second configuration, it is assumed that the battery of accumulators 10 must supply current to the high voltage network, and that its first cells 11 are fully charged.

[0091] In practice, the SOC11 charge level must, for example, be greater than a predetermined charge threshold. This charge threshold is strictly greater than the lower threshold SOCmin. For example, it is 70%.

[0092] Then, the computer 50 drives the controlled switches 15, 16 in the closed state and the DC-DC converter 30 in reverse mode, so that the current from the second cells 12 powers the electric motor 20 (and / or other high-voltage components) if there are any) and that the current from the first cells 11 powers the on-board network 40 and the electric motor 20 (and / or other high-voltage components if there are any).

[0093] This configuration is used as long as the SOC11 charge level of the first cells remains above another predetermined charge threshold. Below this threshold, the computer 50 controls the DC-DC converter 30 in standby mode so that the first cells 11 supply only the on-board network 40.

[0094] This other load threshold is, for example, equal to the lower threshold SOCmin. Alternatively, it may be higher. In any case, it is chosen to guarantee the reliability and operational safety of the vehicle.

[0095] It should be noted that during the discharge of the first cells 11 to power the electric motor 20, the DC-DC converter 30 will be controlled so as to operate at its optimal efficiency. In other words, the current flowing through it will be controlled to remain substantially equal to the optimal current iopt.

[0096] It will also be noted that if, after the DC-DC converter has switched to the stopped state, the charge level SOC11 of the first cells 11 falls below a threshold which is lower than the lower threshold SOCmin and which is considered very low (typically close to the safety threshold SOCsaf), the DC-DC converter 30 can be piloted in the direct state to supply the on-board network 40, or even to recharge the first cells 11 beyond this threshold.

[0097] A third configuration is illustrated in [Fig.4].

[0098] In this third configuration, it is assumed that the battery of accumulators 10 must supply current to the high voltage network, and that the charge of the first cells 11 must be maintained because it is close to the minimum charge.

[0099] So the computer 50 controls the controlled switches 15, 16 in the closed state and the DC-DC converter 30 in direct mode, so that the current from the second cells 12 powers the electric motor 20 and the on-board network 40.

[0100] This configuration, better known by the English term "floating", allows the first cells 11 to be maintained at a charge level SOC11 guaranteeing the safety of the vehicle against any failure.

[0101] It should be noted that the controlled switch 15 could be controlled in the open state, but this is preferably not the case. Indeed, the first cells 11 can be used to compensate for the very rapid variations in current consumed by the on-board network 40, which variations could not be absorbed by the DC-DC converter due to its short reaction time.

[0102] This configuration has the disadvantage that the efficiency of the DC-DC converter 30 is not necessarily optimal. The power supply of the onboard network 40 requires in fact generally a lower intensity than the optimal intensity iopt, so that the DC-DC 30 converter operates below its maximum efficiency.

[0103] The following configuration will then make it possible to overcome this drawback.

[0104] A fourth configuration is thus illustrated in [Fig.5].

[0105] In this fourth configuration, it is assumed that the battery of accumulators 10 must supply current to the high voltage network, that the on-board network 40 consumes a current of lower intensity than the optimal intensity iopt, and that the first cells 11 are not charged up to their upper threshold SOCmax.

[0106] Then the computer 50 controls the controlled switches 15, 16 in the closed state and the DC-DC converter 30 in direct mode, so that the current from the second cells 12 powers the electric motor 20, the first cells 11 and the on-board network 40.

[0107] The objective at this stage is that the intensity of the current consumed by the on-board network 40 and by the load of the first cells 11 is equal to the optimal intensity iopt.

[0108] Conversely, when the charge level of the first cells 11 reaches the upper threshold SOCmax, the control unit 11 can control the supply of power to the on-board network 40 and the electric motor 20 from the first cells 11 (second configuration), so that they discharge, for example, down to the lower threshold SOCmin. For this purpose, the DC-DC converter 30 is controlled in reverse mode.

[0109] Once this lower threshold is reached, the charging of the first cells 11 can resume (fourth configuration) in order to optimize the operation of the DC-DC converter 30 in direct mode again.

[0110] A fifth configuration is illustrated in [Fig.6].

[0111] This configuration is used as a variant of the second and fourth configurations.

[0112] In this fifth configuration, the battery of accumulators is considered 10 must supply current to the high voltage network, and the on-board network 40 consumes a current of lower intensity than the optimal intensity iopt.

[0113] So, the computer 50 controls the controlled switches 15, 16 in the closed state and the DC-DC converter 30 in the stopped mode, so that the current from the second cells 12 powers the electric motor 20, and the current from the first cells 11 powers the on-board network 40. This configuration avoids operating the DC-DC converter 30 with low efficiency.

[0114] A sixth configuration is illustrated in [Fig.7].

[0115] In this sixth configuration, it is assumed that the vehicle control lever is in parking mode and that the high voltage network is not consuming any electrical current.

[0116] Then (for example, immediately or, alternatively, when the vehicle has been parked for a predetermined period), the control unit 50 drives the controlled switches 16 to the open state so as not to use the DC-DC converter 30, which has very low efficiency. Therefore, only the electrical current from the first cells 11 powers the on-board network 40.

[0117] It should be noted that this configuration allows the vehicle occupants to use functions of the on-board network 40, for example the radio.

[0118] Alternatively, other configurations could be used and other adjustments could be made.

[0119] This sixth configuration is advantageous because of the total capacity of all the first cells 11.

[0120] Indeed, this capacity is here in the order of 400 Ah, which is much higher than a standard lead-acid battery capacity, which is in the order of 100 Ah.

[0121] Therefore, the first cells 11 can power the on-board network for a very long time without requiring any charging. However, in modern vehicles, when the vehicle is parked, the on-board network 40 can consume more current than before, for example, if the vehicle owner wants the vehicle's cameras to remain active. In such a configuration, it was necessary to recharge the lead-acid battery several times a day while the vehicle was parked, using the main battery. Thanks to the invention, it is no longer necessary to perform this charging so often (by activating numerous electronic components of the vehicle, which consumed a significant amount of current).

[0122] These different configurations therefore make it possible to illustrate simply how the accumulator battery 10 can be used.

[0123] In the following, we will be able to give some additional examples allowing us to make the best use of the architecture of this battery.

[0124] Typically, in [Fig.2], the first configuration of the system is shown, in which the charger 21 is connected to the external electrical network 100, which allows all the cells of the accumulator battery 10 to be recharged.

[0125] This configuration, while effective when the external electrical network 100 delivers a direct current voltage, is not as effective when the external electrical network 100 delivers an alternating current voltage. Indeed, for such a load, an AC-DC converter is used to rectify the voltage.

[0126] However, this AC-DC converter has an efficiency that varies like that of the DC-DC converter, so it is preferable not to use it for low intensity currents.

[0127] Therefore, the operating mode where all cells are recharged together is not optimal since the DC-DC converter and the AC-DC converter are not used at their best efficiency.

[0128] It is known, in particular, that as the charge level of the battery cells increases, the charging current must decrease. The risk is therefore that at the end of the charging process, the charging current used will be low and the efficiency of the DC-DC and AC-DC converters will be degraded.

[0129] On [Fig.8], three curves were then shown illustrating how the DC-DC converter 30 can be driven to ensure the charging of the cells.

[0130] The first curve illustrates the variation over time t of the charge level SOC 12 of the second cells 12.

[0131] The second curve illustrates the variation over time t of the electrical power delivered by the DC-DC converter 30.

[0132] The third curve illustrates the variation over time t of the charge level SOC 11 of the first cells 12.

[0133] Initially, the DC-DC converter 30 is driven in the off state, so that only the second cells 12 are charged. Since the SOC12 charge level of the second cells 12 is initially reduced, the charging current intensity is then high, so that the efficiency of the AC-DC converter remains high.

[0134] The intensity of the charging current then gradually decreases during charging. During this charging, the first cells 11 supply the on-board network 40 and therefore discharge.

[0135] Before the second cells 12 are fully charged, the DC-DC converter is driven in forward operation so that it delivers a current of approximately equal intensity to the optimal intensity. This supplies the on-board network 40 and the first cells 11, which are then recharged.

[0136] Then, when the second cells 12 are completely changed, the power and efficiency of the converter decrease to finish charging the first cells as needed.

[0137] If the charger remains connected and the vehicle remains unused for a long period (in practice more than a year), the charge level of the first cells may have decreased below a threshold (SOCsaf), so that the joint charging process of the first and second cells may start again.

[0138] On the other hand, if the charger is disconnected and the vehicle remains unused for a long period (in practice more than a year), the charge level of the first cells may have dropped below a certain threshold, so that a process known as "baby-feeding" may be carried out. This process consists of waking up the vehicle's electronic components, closing the controlled switches 15, 16, and then... command the DC-DC converter 30 in direct state so that the second cells 12 recharge the first cells 11. This feeding process is current-consuming in that it requires waking up electronic components of the vehicle, but thanks to the high total capacity of the first cells, it is only rarely implemented.

[0139] It should be noted that if the first cells 11 are very discharged at the start of charging (with a charge level SOC11 below a charge threshold, typically below the lower threshold SOCmin or the safety threshold SOCsaf), then the first and second cells 11, 12 can be charged simultaneously at the best efficiency of the DC-DC converter. When the first cells are sufficiently charged (for example, to the upper threshold SOCmax), the DC-DC converter can be switched off. The charging of the second cells 12 can then proceed in the conventional manner.

[0140] It should also be noted that in the case where, during charging, the on-board network 40 consumes an intensity greater than or equal to the optimal intensity iopt, the DC-DC converter 30 can be controlled in the direct state so that the second cells 12 (and / or the charger) supply this on-board network 40 at this optimal intensity, the remaining intensity being supplied by the first cells 11.

[0141] As described previously, when the first cells 11 are very discharged, it will be possible to increase the current through the DC-DC converter 30 to recharge them.

[0142] During a cold start (typically below 0°C), it is known that battery cells are not able to deliver the same current as when they are at a higher temperature.

[0143] So, the second cells 12 will not necessarily be able to meet the current demand of the electric motor 20. Therefore, the computer 50 will be able to control the DC-DC converter 30 in reverse mode, so that the first cells 11 participate in meeting this demand.

[0144] When the vehicle has to brake, it is known to use the electric motor 20 as an alternator, so that it transforms the braking energy into electrical energy to charge the accumulator battery 10. This is called regeneration.

[0145] However, when the battery is cold or the second cells 12 have a very high charge level SOC12 (typically greater than or equal to the upper threshold SOCmax), this regeneration is no longer possible.

[0146] Here, in this eventuality, the DC-DC converter 30 can be driven in direct state and at the maximum current imax (thus exploiting the large capacity of the first cells 11) so that the electrical energy from braking powers the on-board network 40 and recharges the first 11 cells (provided that their charge level is not greater than or equal to the upper threshold SOCmax).

[0147] The present invention is in no way limited to the embodiments described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0148] Typically, the first and second cells could be of different types and / or deliver different individual voltages. The objective is that the first cells connected together deliver a voltage substantially equal to the voltage required by the on-board network 40, and that the second cells connected together deliver a voltage substantially equal to the voltage required by the high-voltage network.

[0149] In the examples given above, the DC-DC converter 30 is driven as much as possible to deliver a current equal to the optimal current iopt. Of course, since its efficiency remains high within a known current range (typically from 25A to 250A), the converter can be driven to deliver a current different from the optimal current iopt, provided it remains within this range.

[0150] More generally, the present invention could be applied to devices other than a car, in particular a boat comprising two electrical networks operating at different voltages. It could also be applied to non-mobile devices, for example, solar installations comprising batteries used in a second-life application (these batteries having been previously used in motor vehicles). In all cases, the device will comprise two electrical networks supplied at different voltages, a battery equipped with a charger, and a DC-DC converter.

Claims

Demands

1. Device (1) comprising: - a first electrical network (40) operating at a first voltage, - a second electrical network operating at a second voltage higher than the first voltage, - a battery (10), and - a charger adapted to charge the battery (10) and operating on one of the first and second voltages, characterized in that the battery (10) comprises a casing (13) which houses first battery cells (11) and second battery cells (12) adapted to be electrically isolated from the first battery cells (11), and from which emerge first terminals (18) for connecting the first battery cells (11) to the first electrical network (40) and second terminals (19) for connecting the second battery cells (12) to the second electrical network, and in that a DC-DC converter (30) is provided which is connected, on one side, to the second connection terminals (19), and,on the other hand, to the first electrical network (40) and which is controlled by a computer (50).

2. Device (1) according to claim 1 formed by a motor vehicle (1), wherein the first electrical network is an on-board electrical network (40) and the second electrical network comprising at least one load formed by an electric motor (20) for the propulsion of the motor vehicle (1).

3. Device (1) according to claim 1 or 2, wherein the housing (13) contains: - a single battery management system (14) adapted to communicate with the first and second battery cells (11, 12), - at least one first switch (15) interposed between one of the first terminals (18) and the first electrical network (40), - at least one second switch (16) interposed between one of the second terminals (19) and a load of the second electrical network, the first and second switches (15, 16) being controlled by the battery management system (14), and - preferably, a cooling and / or heating circuit adapted to cool and / or heat the first and second battery cells (11, 12).

4. Device (1) according to any one of claims 1 to 3, wherein the first and second battery cells (11, 12) are all identical.

5. A method for controlling a DC-DC converter (30) of a device (1) according to any one of claims 1 to 4, wherein it is provided to characterize an operating point of the device (1) and to control the DC-DC converter (30) according to the operating point between: - a forward state in which the current from the second battery cells (12) supplies at least the first electrical network (40), - an inverted state in which the current from the first battery cells (11) supplies at least one load (20) of the second electrical network, and - optionally, a stopped state in which the second battery cells (12) are electrically isolated from the first battery cells (11) and the first electrical network (40).

6. A control method according to claim 5, wherein, when the load (20) is supplied with current by the second battery cells (12), it is provided to: - determine a charge level (SOC11) of the first battery cells (11), then - at least if the measured charge level (SOC11) exceeds a first threshold, control the DC-DC converter (30) in reverse state, preferably at an intensity maximizing the efficiency of the DC-DC converter (30).

7. A control method according to any one of claims 5 and 6, wherein, when the load (20) is supplied with current by the second battery cells (12), it is provided that: - a charge level (SOC11) of the first battery cells (11) is determined, and then - at least if the measured charge level (SOC11) is below a second threshold, the DC-DC converter (30) is driven in forward operation such that the second battery cells (12) supply the first electrical network (40) and recharge the first cells of battery (11), preferably at an intensity maximizing the efficiency of the DC-DC converter (30).

8. A control method according to claim 7, wherein if the measured load level (SOC11) is greater than the second threshold, the DC-DC converter (30) is intended to be controlled in reverse state.

9. A control method according to any one of claims 5 to 8, wherein, when the load (20) is supplied with current by the second battery cells (12), it is provided to: - determine the intensity of the current consumed by the first electrical network (40), then - at least if the measured intensity is less than a third threshold, control the DC-DC converter (30) in the stopped state so that only the first battery cells (11) supply the first electrical network (40).

10. A control method according to any one of claims 5 to 9, wherein, when the load (20) is at rest, the DC-DC converter (30) is controlled in the stopped state such that only the first battery cells (11) supply the first electrical network (40).

11. A control method according to any one of claims 5 to 10, wherein, when the battery of accumulators (10) is connected to an external charging network (100) via the charger, it is provided that: - first, the DC-DC converter (30) is driven in the stopped state such that only the first battery cells (11) supply the first electrical network (40) and only the second battery cells (12) are charged, then - before the second battery cells (12) are fully charged, the DC-DC converter (30) is driven in the forward state such that the first and second battery cells (11, 12) are charged, the current through the DC-DC converter (30) being preferably maintained at a value maximizing the efficiency of the DC-DC converter (30).