ELECTRICAL SYSTEM FOR PRECHARGING A CAPACITY ARRANGED BETWEEN POSITIVE AND NEGATIVE LINES CONNECTABLE TO A BATTERY

Abstract

The invention relates to an electrical system (10) comprising an electric battery having a positive terminal (11) and a negative terminal (12), a first positive line (L1), a second negative line (L2), a first contactor (S1) interposed between the positive terminal and the first line (L1), a second contactor (S2) interposed between the negative terminal and the second line, a reservoir capacity (CR) interposed between the first line and the second line, the system comprising a precharging circuit, connected on the one hand to the second line and on the other hand to the negative terminal, the precharging circuit comprising in series an inductance (LPC) and a control transistor (T1) configured to be controlled by a control unit (4), the control transistor being controlled, after closing the first contactor and before closing the second contactor, according to a pumping cycle control to charge the reservoir capacity. Figure 1

Description

Title of the invention: ELECTRICAL SYSTEM FOR PRECHARGING A CAPACITY ARRANGED BETWEEN POSITIVE AND NEGATIVE LINES CONNECTABLE TO A BATTERY

[0001] The invention relates to an electrical system for precharging a capacity arranged between positive and negative lines connectable to a battery.

[0002] In an electric vehicle, an electric battery is provided having a positive terminal and a negative terminal. The terminals of the battery are intended to be connected respectively to a first positive line and to a second negative line, forming a network head, for example high voltage, in the context of the present invention.

[0003] The connection is not permanent, the battery can be electrically isolated from the first and second lines, in particular for phases of non-use.

[0004] For this purpose, a first contactor is provided interposed between the positive terminal and the first line, and a second contactor interposed between the negative terminal and the second line.

[0005] A reservoir capacity is also provided between the first line and the second line. This capacity acts as a filter to attenuate current draws which may occur in the electrical consumers connected to the downstream network between the first line and the second line.

[0006] When it is desired to close the first contactor and the second contactor to supply the first and second lines, the charging of this reservoir capacity generates, without any other precaution or specific device, a current peak called on the terminals of the battery. This current peak must be avoided to maximize the battery life and avoid deterioration of the electrical contact areas of the first and second contactors by electric arcing.

[0007] To minimize this current peak, it has been proposed to have, in parallel with the first contactor, a selectively activated resistive circuit, which is activated after the second contactor closes and before the first contactor closes. Thus, by delaying the closing of the contactor on the positive line, time is allowed for the reservoir capacity to charge at limited current, before establishing the power supply via the two closed contactors.

[0008] However, such a selectively activated resistive circuit includes an electronic switch which must meet insulation recommendations linked to the high voltages which it interfaces, and in addition electrical energy is wasted by the Joule effect in the re- resistance placed in series on this resistive circuit.

[0009] The inventors therefore sought to propose new solutions for managing the pre-charging of the tank capacity in an optimized manner.

[0010] For this purpose, the present invention proposes an electrical system comprising an electric battery having a positive terminal and a negative terminal, a first positive line, a second negative line, a first contactor interposed between the positive terminal and the first line, a second contactor interposed between the negative terminal and the second line, at least one reservoir capacity interposed between the first line and the second line, characterized in that the system comprises a precharging circuit, connected on the one hand to the second line and on the other hand to the negative terminal of the battery, the precharging circuit comprising in series at least one inductor and a control transistor configured to be controlled by a control unit, the control transistor being controlled, after closing the first contactor and before closing the second contactor, according to a cyclic pumping control to charge the reservoir capacity.

[0011] Advantageously, the reservoir capacity is precharged via the negative terminal.

[0012] Thanks to the provisions promoted above, the control transistor benefits from reduced isolation conditions if compared to the control on the positive terminal side. The control transistor is referenced with respect to the negative terminal so the need for isolation is simplified if compared with a precharge via the positive terminal.

[0013] It is noted that one of the results obtained is to improve the closing conditions of the contactors to avoid electric arc phenomena on the contacts at the time of closing the contactors (i.e. at the time of establishing the current).

[0014] In addition, the use of an inductance makes it possible to reduce losses due to the Joule effect.

[0015] The cost of the proposed solution is advantageous compared to that of a power resistor with a relay used in known solutions.

[0016] It is noted that the time to charge the reservoir capacity is of the order of a few tens or hundreds of milliseconds.

[0017] It should be noted that the control unit may typically be the unit called the battery management computer ('BMS').

[0018] It is noted that the first and second contractors may typically be relays. However, it is not excluded to use other electromechanical devices or power semiconductors to form the first and second contractors.

[0019] According to one embodiment, the control is cycled so that the current flowing through the inductor remains below a saturation limit, said saturation limit being defined relative to a magnetic saturation of the inductor.

[0020] The average current in the inductance is maximized, without saturating it, to reduce and even minimize the charging time.

[0021] According to one embodiment, a first measuring shunt is provided, capable of allowing measurement of the current passing through the inductance.

[0022] The control unit can acquire a reading of the voltage across said first measuring shunt, and directly deduce therefrom the current flowing through the inductor.

[0023] According to one embodiment, a freewheel diode is provided, establishing a return circuit for electromagnetic energy stored in the inductance. This return circuit is established when the control transistor is closed, i.e. not conducting. Thanks to this freewheel diode and this return circuit, the energy which was contained in the inductance is discharged into the reservoir capacity.

[0024] According to one embodiment, a second measuring shunt is provided, capable of allowing measurement of the current delivered by the battery.

[0025] Thus, the control unit can acquire a reading of the voltage across the terminals of said second measuring shunt, and deduce therefrom the current entering and leaving the battery. This allows the control unit when formed by the battery management computer (called BMS) to continuously calculate a current state of charge of the battery. This also makes it possible to provide protection against excessively high currents.

[0026] According to one embodiment, the nominal battery voltage is at least equal to 48 Volts. The usefulness of the present invention is all the more important as the voltage at the terminals of the battery is high. The creation of an arc when the contactors are closed is thus eliminated.

[0027] According to one embodiment, the nominal battery voltage may be approximately 400 V. According to one embodiment, the nominal battery voltage may be approximately 800 V. Of course, other nominal battery voltages are also considered here. Even for high voltages, the pre-charging circuit prevents the creation of an arc when the contactors are closed.

[0028] According to one embodiment, the control transistor may be a field effect transistor (Mosfet) or an insulated gate bipolar transistor (IGBT). In this way, a component with good market availability, reasonable cost and good reliability, and good cycling capacity is chosen to chain the ON and OFF commands.

[0029] According to one embodiment, a non-return diode is provided, in series with the inductance, protecting the control transistor from a polarity reversal. Thanks to which, even if a polarity reversal is inadvertently carried out, the control transistor will not be damaged.

[0030] According to one embodiment, the control unit is configured to stop the control cycle of the control transistor and to control the closing of the second contactor as soon as a condition on the voltage across the reservoir capacitor is verified.

[0031] In practice, for the said condition, a coefficient KS can be chosen such that VI - V2 > KS (VP - VN), with VP the voltage of the positive terminal of the battery, VN the voltage of the negative terminal of the battery, VI the voltage on the first line, V2 the voltage on the second line. The coefficient KS = 0.97 can be chosen. In other words, it remains to establish at most 3% of the voltage at the terminals of the battery by closing the second contactor. The closing of the second conductor then occurs without arcing.

[0032] The invention further relates to a vehicle comprising an electrical system as described above.

[0033] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: [Fig.l] is a representation of an example of an electrical diagram of the proposed system; [Fig.2] illustrates a timing diagram of the process of precharging the reservoir capacity.

[0034] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the description, certain elements are not necessarily represented to scale.

[0035] The electrical system proposed herein may be installed on board a motor vehicle. The motor vehicle in question may be a passenger car, a utility vehicle, a truck, a bus, a recreational vehicle, etc. There is no limitation on the type of target vehicle.

[0036] Similarly, the electrical system proposed here can be installed on equipment that is not a motor vehicle, it can be stationary equipment, railway equipment, maritime equipment, aerial equipment.

[0037] To return to the case of the electric vehicle, the present invention is particularly relevant for the case of an electric vehicle, whether hybrid or 100% electric.

[0038] In this case, an electrical energy storage battery marked B ATT in the figures is provided.

[0039] The electric battery has a positive terminal 11 at potential VP and a negative terminal 12 at potential VN.

[0040] The battery in question has a nominal voltage at its terminals VP - VN. According to one embodiment, the nominal voltage at the terminals of the battery may be 48 volts, for example in the case of a hybrid vehicle. In the case of a 100% electric vehicle, the nominal voltage at the terminals of the battery may be around 400 volts. According to another 100% electric embodiment, the nominal voltage at the battery terminals can be around 800 volts. The present invention works regardless of the nominal voltage of the battery.

[0041] The energy storage capacity of the battery can be a few kilowatt hours or a few tens of kilowatt hours.

[0042] The electrochemical technology of the battery can be any, for example in the Lithium-ion family.

[0043] The battery is usually associated with a battery management computer called in the jargon BMS (from the English Battery Management System). The functions of this unit are known per se and therefore not detailed here.

[0044] The electrical system comprises a control unit 4 which, in the example presented, corresponds to the BMS calculator, but it could be otherwise.

[0045] The electrical system comprises a first positive line L1, a second negative line L2. The first and second lines L1, L2 form the head end of the high voltage network. Consumers, such as an electrical machine inverter or a DC / DC converter, can be connected to this high voltage network.

[0046] The electrical system comprises a first contractor S1 interposed between the positive terminal 11 and the first line L1, and a second contractor S2 interposed between the negative terminal 12 and the second line L2.

[0047] The first and second contractors SI and S2 may typically be relays. However, it is not excluded to use other electromechanical devices or power semiconductors to form the first and second contractors SI and S2.

[0048] The first and second contactors allow the high voltage network to be isolated from the battery. Thus, although the battery remains live, it is possible to work safely on lines L1 and L2 when the contactors S1 and S2 have been opened.

[0049] The electrical system comprises a reservoir capacity CR interposed between the first line L1 and the second line L2.

[0050] In the example illustrated in [Fig.l], only one reservoir capacity is shown, but in practice there may be several reservoir capacities arranged in parallel.

[0051] The single reservoir capacitance or the reservoir capacitances in parallel may have a capacitance value between 500 microFarad and 2000 microFarad.

[0052] The positive terminal of the reservoir capacity is connected to the first electrical line L1, and the negative terminal of the reservoir capacity VK is connected to the second electrical line L2.

[0053] The CR reservoir capacity acts as a filter to attenuate current draws which may occur in electrical consumers connected to the downstream network. between the first line L1 and the second line L2.

[0054] However, when moving from a situation where the first and second contactors S1, S2 were open and it is desired to close them again, provision is made to use a pre-charging circuit which prevents the contact elements of the contactors from undergoing an arc caused by a current draw from the consumers on the network (said consumers also quite often have a local reservoir capacity to charge).

[0055] The electrical system therefore comprises a precharging circuit 2. According to the proposed device, the precharging circuit 2 is located in parallel with the second contactor S2 and it is used after the closure of the first contactor S1 while the second contactor S2 is not yet closed.

[0056] The precharge circuit 2 comprises an inductance denoted LPC and a control transistor denoted Tl, arranged in series.

[0057] The control transistor Tl is a field effect transistor (Mosfet) or an insulated gate bipolar transistor (IGBT).

[0058] Alternatively, the control transistor T1 may be a bipolar transistor, a silicon carbide (SiC) transistor or a gallium nitride (GaN) transistor.

[0059] With reference to [Fig. 1], the current which flows in the inductance LPC, and in the control transistor Tl when it is on, is noted Ipc.

[0060] On the precharge circuit 2 there is also a first measuring shunt denoted RL. The first measuring shunt RI is placed in series with the inductance LPC.

[0061] Two read-back lines Ya and Yb are also provided, each of which takes the voltage from one of the terminals of this measurement shunt RL. The measurement of the voltage difference Yb-Ya, divided by the resistance of the shunt RI, makes it possible to obtain an image of the current Ipc which crosses the inductance.

[0062] When the control transistor goes from OFF to ON, it allows the current Ipc to pass through the inductor, and said current gradually increases from zero due to the self-inductance effect of this inductor or coil.

[0063] Advantageously, it is provided that the current flowing through the inductance remains below a saturation limit Isat, said saturation limit being defined with respect to a magnetic saturation of the inductance.

[0064] In addition, a freewheel diode D2 is provided, establishing a return circuit for electromagnetic energy stored in the inductance. This return circuit is established when the control transistor T1 is closed, i.e. not conducting. Thanks to this freewheel diode D2 and this return circuit, the energy which was contained in the inductance is discharged into the reservoir capacitor CR.

[0065] In addition, a non-return diode is provided, in series with the inductance.

[0066] In the example illustrated, the anti-return diode DI is interposed between the inductance and the control transistor T1 but it could be downstream of the transistor TL.

[0067] The anti-return diode DI protects the control transistor from reverse polarity.

[0068] It is noted that a fuse F is provided between the positive terminal of the VP battery and the first contactor SI.

[0069] On the second line L2, a second measuring shunt denoted R2 is provided. The second measuring shunt R2 allows a measurement of the current delivered by the battery.

[0070] The second measuring shunt R2 is interposed between the negative terminal VN of the battery and the second contactor S2.

[0071] Read-back lines respectively marked G1 and G2 are provided to allow the control unit 4 to measure the potential difference across the terminals of the measuring shunt and to deduce therefrom the current flowing through the measuring shunt R2.

[0072] The resistance value of this shunt R2 in ohms is very low, e.g. a few milli-ohms at most.

[0073] The electrical voltage prevailing on the first line L1 is noted VL

[0074] The electrical voltage which prevails on the second line L2 is noted V2.

[0075] The negative terminal of the reservoir capacity CR is noted VK, its electrical potential is equal to the voltage V2.

[0076] The voltage V2 is measured using the rereading line marked Yb in [Fig.l].

[0077] It should be noted that the voltages VI,V2 of the first and second lines L1,L2 are generally floating with respect to the electrical ground of the vehicle.

[0078] The control unit 4 is configured to stop the cycled control of the control transistor as soon as a stop condition on the voltage across the reservoir capacitor (VI-V2) is verified.

[0079] Simultaneously or shortly after, the control unit can then command the closing of the second contractor S2.

[0080] For the stopping condition, we can choose a coefficient KS such that VI- V2 > KS (VP - VN), with KS = 0.97.

[0081] On the timing diagram of [Fig.2], the instant ttl corresponds to the closing of the first contactor SL

[0082] At time ttl, or just after, the control unit 4 activates the control transistor Tl which becomes conducting. The voltage VI instantly becomes equal to the positive voltage VP, while the voltage V2 is pulled upwards by the reservoir capacitor CR discharged at this time.

[0083] The current Ipc which passes through the inductance increases from 0 according to an exponential. At the moment when the current Ipc approaches the saturation current Isat, at the end of the first period noted 41, at the instant tt2, the control unit 4 deactivates the control transistor T1 which becomes blocked.

[0084] During the first period noted 41, the voltage VK decreases.

[0085] From time tt2, the current Ipc decreases towards 0. Note that the current is redirected by diode D2 towards the reservoir capacitor CR.

[0086] During the second period noted 42, the reservoir capacity CR continues to charge, and the voltage VK continues to decrease.

[0087] The cycling described above, with a first activation period of the transistor 41 and a second blocking period of the transistor 42 is repeated, as many times as necessary, until the charge of the reservoir capacity is sufficient or expressed otherwise until the voltage V2 is close to the negative voltage VN of the battery.

[0088] In practice, the control unit 4 is configured to stop the cycled control of the control transistor T1 and to control the closing of the second contactor S2 as soon as a condition on the voltage across the terminals of the reservoir capacitor is verified.

[0089] According to an exemplary embodiment, for said condition it is possible to choose a coefficient KS such that VI- V2 > KS (VP - VN).

[0090] According to an exemplary embodiment, KS = 0.97 can be chosen.

[0091] This condition corresponds to the threshold marked Vs in [Fig.2].

[0092] In [Fig.2], at time tt3, the condition becomes true, then the control unit 4 interrupts the cycling of the control transistor and leaves it in the blocked state, then it commands the closing of the second contactor S2.

[0093] From this moment, the high voltage network of lines L1 and L2 is completely connected (at low impedance) to the terminals of the battery VP and VN, the precharge circuit 2 is short-circuited.

[0094] We note that the first measuring shunt RI allows currents of 3 to 5 amperes to be measured.

[0095] It is noted that the durations of periods 41 and 42 are of the order of a few microseconds.

[0096] The repetition frequency of periods 41 and 42 can be fixed or adapted in real time depending on whether Ipc reaches the current thresholds Isat and 0.

[0097] The time to charge the reservoir capacity CR is of the order of a few tens or hundreds of milliseconds, for example 200 milliseconds.

Claims

Claims

1. Electrical system (10) comprising an electric battery having a positive terminal (11, VP) and a negative terminal (12, VN), a first positive line (L1), a second negative line (L2), a first contactor (SI) interposed between the positive terminal and the first line (L1), a second contactor (S2) interposed between the negative terminal and the second line (L2), at least one reservoir capacity (CR) interposed between the first line and the second line, characterized in that the system comprises a precharging circuit, connected on the one hand to the second line (L2) and on the other hand to the negative terminal (12) of the battery, the precharging circuit comprising in series at least one inductance (LPC) and a control transistor (T1) configured to be controlled by a control unit (4), the control transistor being controlled, after closing the first contactor and before closing the second contactor,according to a cycled pumping command to charge the reservoir capacity.,

2. Electrical system according to claim 1, characterized in that the control is cycled so that the current (Ipc) passing through the inductance remains below a saturation limit (Isat), said saturation limit being defined with respect to a magnetic saturation of the inductance (LPC).

3. Electrical system according to any one of claims 1 to 2, characterized in that a first measuring shunt (RI) is provided, capable of allowing a measurement of the current (Ipc) passing through the inductance.

4. Electrical system according to any one of claims 1 to 3, characterized in that a freewheel diode (D2) is provided, establishing a return circuit for electromagnetic energy stored in the inductance.

5. Electrical system (1) according to any one of claims 1 to 4, characterized in that a second measuring shunt (R2) is provided, capable of allowing measurement of the current delivered by the battery.

6. Electrical system (1) according to any one of claims 1 to 5, characterized in that the nominal battery voltage is at least equal to 48 Volts.

7. Electrical system (1) according to any one of claims 1 to 6, characterized in that the control transistor (Tl) is a field effect transistor (Mosfet) or an insulated gate bipolar transistor (IGBT).

8. Electrical system according to any one of claims 1 to 7, characterized in that an anti-return diode is provided, in series with the inductance, protecting the control transistor from a polarity reversal.

9. Electrical system (1) according to any one of claims 1 to 8, characterized in that the control unit is configured to stop the cycled control of the control transistor and to control the closing of the second contactor (S2) as soon as a condition on the voltage across the reservoir capacity (VI-V2) is verified.

10. An electric motor vehicle comprising an electrical system according to any one of claims 1 to 9.

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