Pre-charging device for power network

Abstract

The invention relates to a device (10) for precharging an electric power network, the device comprising: a power supply line (L1) for supplying power to the electric power network (10), the power supply line comprising a main transistor (Q1); a control module (12) for controlling the main transistor, the control module being designed to limit the intensity of the current flowing through the power supply line; and a power supply module (14) for supplying power to the control module, the power supply module being connected to the power supply line on both sides of the main transistor.

Description

Technical Field

[0001] The present invention generally relates to an electrical power network architecture for an electrically driven motor vehicle.

[0002] More specifically, the invention relates to a pre-charging device for pre-charging an electric power network, in particular to a pre-charging device for pre-charging an electric power network of such a motor vehicle. Background Art

[0003] The on-board electrical power network of an electrically driven vehicle generally comprises a battery equipped with protective fuses and a set of electrical consumers, which will be referred to hereinafter as “electrical loads” and include in particular an electric motor and an inverter.

[0004] In practice, the electrical load comprises capacitors of very high capacitance. It is therefore necessary to pre-charge the electrical network before connecting the battery to the network in order to avoid damage to switching elements such as relays or contactors.

[0005] For this purpose, pre-charging circuits are used, which allow charging the capacitors of the power network before closing the circuit using switching elements (pre-charging contactors, relays, etc.).

[0006] The pre-charging relay is controlled to close when the electric vehicle is started and to open after the pre-charging is completed. The pre-charging relay is connected in series with the element to limit the current in the power circuit to an acceptable value to avoid damaging the power network.

[0007] Document FR 2771863 describes such a set of devices. In this document, the pre-charging device consists of a thermistor whose resistance limits the inrush current of the electrical load during the pre-charging sequence. In the event of a short circuit in the power network, the internal resistance of the thermistor increases significantly, thus automatically limiting the fault current.

[0008] The main disadvantage of the above solution is that the internal resistance value of the thermistor is very dependent on the ambient temperature; this is a big limitation in environments with large ambient temperature variations.

[0009] The solution also requires using different thermistors depending on the characteristics of the power network for each type of vehicle and creating diversified components. Summary of the invention

[0010] In order to make up for the shortcomings of the prior art, the present invention proposes a pre-charging device for pre-charging the power network of an electric-drive motor vehicle, the pre-charging device comprising:

[0011] - a power supply line for supplying power to the power network, the power supply line comprising a main transistor,

[0012] a control module for controlling the main transistor, the control module being suitable for limiting the amplitude of the current flowing through the power supply line, and

[0013] - A power supply module for supplying power to said control module, which power supply module is connected to the power supply line on both sides of the main transistor (so as to deliver the energy required for the operation of the group of devices).

[0014] Thus, by virtue of the present invention, the operation of the pre-charging device is independent of the ambient temperature.

[0015] The pre-charging device can further be implemented with very cheap, compact, reliable and electromagnetic interference insensitive electrical components.

[0016] The architecture of the pre-charging device further allows it to replace the connection of the pre-charging resistor with its two connection terminals.The invention aims to draw the electrical energy required for its operation directly from the main line for a short period before the pre-charging starts.

[0017] The following are other advantageous and non-limiting features of the pre-charging device according to the invention:

[0018] - providing a housing and two connection terminals protruding just from said housing, which are connected to the power supply line on both sides of the main transistor;

[0019] - the power module comprises only passive electrical components;

[0020] - the power supply module is suitable for delaying the activation of the control module relative to the moment of appearance of a potential difference across the terminals of the main transistor, so as to store sufficient energy to supply the control module for the entire duration of the pre-charging;

[0021] - the control module comprises exactly one transistor connected to the main transistor;

[0022] - the power module and the control module are designed to control the main transistor in linear mode during pre-charging of the power network;

[0023] - the power module is suitable for generating current pulses;

[0024] - the control module is adapted to limit the amplitude of the current flowing through the main transistor to below a predetermined threshold;

[0025] - the control module is adapted to adjust the amplitude of the current flowing through the main transistor to a predetermined value within a predetermined time period;

[0026] - the control module comprises an integrated circuit suitable for controlling the main transistor in pulse width modulation mode during pre-charging of the power network;

[0027] - the power supply circuit comprises a coil;

[0028] - the control module comprises an operational amplifier;

[0029] - the control module is adapted to modulate the current amplitude during pre-charging of the power network to a first value during a first time period and then to a second value during a second time period, the second value being at least three times the first value;

[0030] -The control module comprises a pulse width modulation circuit.

[0031] The present invention also relates to an electric power network, comprising:

[0032] - batteries,

[0033] - capacitors,

[0034] - two main connecting lines connecting the terminals of the battery to the terminals of the capacitor and at least one of which comprises a main relay,

[0035] A pre-charging circuit which is connected in parallel with one of the two main connecting lines and comprises a pre-charging relay and a pre-charging device as described above. DETAILED DESCRIPTION

[0036] The description given by way of non-limiting examples with reference to the accompanying drawings will make it easier to understand what the invention consists of and how it can be implemented.

[0037] In the attached picture:

[0038] [ Figure 1 ] is a schematic diagram of a power network of the present invention;

[0039] [ Figure 2 ] is used for Figure 1 A schematic diagram of a pre-charging device for pre-charging a power network in FIG.

[0040] [ Figure 3A ]yes Figure 2 A circuit diagram of a first embodiment of a pre-charging device in;

[0041] [ Figure 3B ] is to show Figure 1 A graph showing the voltage across the terminals of a capacitor of an electric power network as a function of time;

[0042] [ Figure 3C ] is to show the supply to Figure 1 A graph showing the variation of the current amplitude of a capacitor of an electric power network with time;

[0043] [ Figure 4A ]yes Figure 3A A circuit diagram of a variant of the pre-charging device in;

[0044] [ Figure 4B ] is a demonstration of the Figure 4A A graph showing the voltage across the terminals of a capacitor of a power network as a function of time when the pre-charging device is in the power network;

[0045] [ Figure 4C ] is a demonstration of the Figure 4A a graph showing the variation of the current amplitude of the capacitor supplied to the power network with time when the pre-charging device is in the embodiment of the present invention;

[0046] [ Figure 5A ]yes Figure 3A A circuit diagram of a variant of the pre-charging device in;

[0047] [ Figure 5B ] is a demonstration of the Figure 5A A graph showing the voltage across the terminals of a capacitor of a power network as a function of time when a pre-charging device is used;

[0048] [ Figure 5C ] is a demonstration of the Figure 5A a graph showing the variation of the current amplitude of the capacitor supplied to the power network with time when the pre-charging device is in the embodiment of the present invention;

[0049] [ Figure 6 ]yes Figure 2 Circuit diagram of a second embodiment of the pre-charging device in.

[0050] Firstly, it should be noted that the same or similar elements of the various embodiments and variant embodiments of the present invention shown in the various drawings will be referred to using the same reference numerals as much as possible and will not be described each time.

[0051] It should also be noted that the adjective "connected" (and its derivatives) is used in the electrical sense of the term, when two components are connected together when electrical current can flow from one of the components to the other.

[0052] Figure 1 An electrical power network 1 for an electrically driven motor vehicle is shown.

[0053] This electricity network 1 comprises a battery 2 specially designed for supplying one or more electric traction motors of a motor vehicle.

[0054] The electricity network also comprises a set of electrical installations which have a high capacitance and which will be referred to hereinafter as "capacitors 3" (or "electrical loads"). Among these installations, the device comprises at least one power inverter for powering an electric traction motor.

[0055] The electricity network 1 also comprises two main connection lines 4 , 6 , each connected on one side to one of the terminals of the accumulator 2 and on the other side to one of the terminals of the capacitor 3 .

[0056] Each main connecting line 4 , 6 is provided with a relay 5 , 7 which is able to isolate the battery 2 and the capacitor 3 or to bring them into electrical contact.

[0057] If the battery 2 is connected directly to the capacitor 3 when starting the motor vehicle, high inrush currents will enter the main connecting lines 4 , 6 , resulting in the risk of damaging the relays 5 , 7 or the capacitor 3 itself.

[0058] Therefore, a pre-charging circuit 8 is provided to allow the voltage across the terminals of the capacitor 3 to increase gradually, only after which the two relays 5 , 7 are closed successively.

[0059] The pre-charging circuit 8 is connected in parallel with one of the main connecting lines 4, which is connected to the positive terminal of the battery 2. The pre-charging circuit is equipped with a pre-charging relay 9, which can be controlled to an open state or a closed state, and is equipped with a pre-charging device 10, which is more specifically the subject of the present invention.

[0060] The pre-charging relay 9 and the relays 5, 7 are controlled by a computer and will not be described in detail here since they are not strictly speaking the subject of the present invention.

[0061] like Figure 2 As shown schematically, the pre-charging device 10 includes various components.

[0062] It firstly comprises a housing 11 made of an electrically insulating material, which accommodates all other components of the pre-charging device 10 .

[0063] It also comprises a printed circuit board mounted in the housing 11 and carrying all the electrical components of the pre-charging device 10 .

[0064] The printed circuit board comprises a dielectric substrate on which extend conductive tracks which allow the electrical components of the pre-charging device 10 to be connected to one another.

[0065] In the remainder of this description, the term "circuit" will be used to denote a portion of an electrical circuit formed by one or more electrical tracks and optionally also by one or more electrical components.

[0066] like Figure 2As shown, the pre-charging device 10 first includes a main line L1 , both ends of which are connected to two connection terminals 15 , 16 extending from the housing 11 .

[0067] Since the two connection terminals 15 , 16 are the only components protruding from the housing 11 , it will be understood that the pre-charging device 10 is designed to be simply and easily connected to the pre-charging circuit 8 between the battery 2 and the capacitor 3 .

[0068] The main line L1 of the pre-charging device 10 comprises a main transistor (designated Q1 or Q3 ), which is therefore connected between the two connecting terminals 15 , 16 .

[0069] This transistor may be a bipolar transistor, in which case its collector will be connected to the side of the connection terminal 15 (the side of the battery 2 ) and its emitter will be connected to the side of the connection terminal 16 (the side of the capacitor 3 ).

[0070] As a variant, this transistor may be a field effect transistor, generally a MOSFET, in which case its drain will be connected to the side of connection terminal 15 (to the side of battery 2 ) and its source will be connected to the side of connection terminal 16 (to the side of capacitor 3 ).

[0071] The pre-charging device 10 also includes a control module 12 for controlling the main transistors Q1, Q3. The control module 12 will be specifically designed to limit the amplitude i of the current supplied to the capacitor 3. It is thus possible to prevent the current drawn by the capacitor 3 from reaching the capacitor too quickly. This can also limit the current transfer between the battery 2 and the capacitor 3 in the event of a short circuit.

[0072] The pre-charging device 10 further includes a power module 14 for supplying power to the control module 12 .

[0073] This power supply module 14 is connected to the terminals of the main transistors Q1 , Q3 so that it can draw the current required for its operation directly from the main line L1 .

[0074] The power module 14 includes only passive electrical components to reduce costs.

[0075] Finally, if Figure 2 As shown schematically, it has a delay function 13 which delays the activation of the control module 12 so that the pre-charging device 10 has enough time to store the energy it needs to control the main transistors Q1 , Q3 during the entire pre-charging period.

[0076] Figure 3A FIG. 5 shows two embodiments of the pre-charging device 10 .

[0077] exist Figure 3A In the first embodiment shown, the main transistor Q1 is a bipolar transistor.

[0078] In this embodiment, the power supply module 14 is intended to generate the current pulse after the above-mentioned delay.

[0079] like Figure 3A As shown, for this purpose, the power module 14 comprises a Zener diode D1 , the anode of which is connected to the connection terminal 15 , and the cathode of which is connected to one end of the first electrical line L2 .

[0080] The power supply module further comprises a first resistor R1 having one terminal connected to the connection terminal 16 and having the other terminal connected to the end of the first electric line L2.

[0081] It also comprises a parallel RC circuit which is connected on one side to the other end of the first electrical line L2 and on the other side to the control module 12. The RC circuit here comprises a resistor R2 and a capacitor C1.

[0082] Thus, when a voltage appears across the terminals of the main transistor Q1 , the power module 14 can perform the above-mentioned delay function and generate a calibration pulse.

[0083] The control module 12 comprises a second electrical line L3 which is connected on one side to the parallel RC circuit and on the other side to the control transistor Q2 .

[0084] The second electrical line L3 comprises a diode D2, the anode of which is connected to one side of the parallel RC circuit.

[0085] Control transistor Q2 is the only active electrical component of control module 12 .

[0086] It is controlled to generate an electrical pulse of a predetermined duration. This duration is selected to be equal to the duration required to pre-charge the capacitor 3. Therefore, this duration is set taking into account the current that the main transistor Q1, the pre-charge relay 9 and the capacitor 3 can withstand. For example, it can be about half a second.

[0087] The control transistor Q2 may be of the bipolar type, but a MOSFET is used here instead.

[0088] The drain of the control transistor Q2 is connected to the main transistor Q1, while its source is connected via a resistor R5 to the connection terminal 16. Its gate, for its part, is connected to the second electrical line L3.

[0089] In order to make the generated electrical pulses have the required characteristics to control the main transistor Q1 in a linear mode within the desired period, a filter is used, which includes two resistors R3, R4 and a capacitor C2.

[0090] The two resistors R3, R4 and the capacitor C2 are connected on one side to the connection terminal 15 and on the other side to the second electrical line L3. The resistor R3 is connected on the anode side of the diode D2, while the other two components C2, R4 are connected on the cathode side of the diode D2.

[0091] By virtue of the architecture of the power module 14 and the control module 12 , the main transistor Q1 is controlled in a linear mode.

[0092] The two main criteria to be considered when designing both modules are the power module 14 and the control module 12 , are the time required to pre-charge the capacitor 3 and the current Q1 that the main transistor can withstand (especially in the event of a short circuit).

[0093] Therefore, the resistance and capacitance of the electrical components are selected to meet these two criteria.

[0094] exist Figure 3A In the embodiment shown, both modules, the power module 14 and the control module 12 , are therefore designed to limit the amplitude i of the current flowing through the main transistor Q1 to below a predetermined threshold.

[0095] Figure 3B shows the variation of the voltage across the terminals of capacitor 3 with time, and Figure 3C The variation with time of the amplitude i of the current supplied to the capacitor 3 during pre-charging is shown.

[0096] It can be seen that, according to the invention, the voltage U across the terminals of the capacitor 3 gradually increases and the amplitude i drawn by the capacitor 3 is initially limited to the threshold i max below, and then gradually decreases.

[0097] In practice, when the user wishes to start his motor vehicle, the computer is programmed to leave relays 5 , 7 in the open state and to close pre-charging relay 9 .

[0098] Immediately after the pre-charging relay 9 is closed, it will be noted that the main transistor Q1 remains in the off state during the time that the capacitors C1 , C2 are being charged, which ensures the execution of the above-mentioned delay function.

[0099] Once the power module 24 has stored enough electrical energy, the control transistor Q2 receives an electrical pulse corresponding to the time required to pre-charge the capacitor 3. Then, during this time, the main transistor Q1 is controlled in linear mode, which allows it to limit the amplitude of the current received by the capacitor 3.

[0100] Once the pre-charging is completed, relays 5 and 7 are closed. Finally, the pre-charging relay 9 is controlled to the open state.

[0101] It should be noted that the pre-charging device 10 allows limiting the current flowing through the main transistor Q1 in the event of a fault such as a short circuit in the capacitor 3, thus avoiding any damage. In this case, the computer can be programmed to detect such a fault (for example, by detecting that the voltage across the terminals of the capacitor 3 does not increase) and to quickly disconnect the pre-charging relay 9.

[0102] In any case, at the end of these operations, if the conditions required for the operation of the pre-charging device 10 appear again (if the pre-charging relay 9 is closed again and a potential difference appears across the terminals of the main transistor Q1), the pre-charging device is then ready to be reactivated (i.e. automatically reset).

[0103] Figure 4A Shows Figure 3A A variant embodiment of the pre-charging device 10 in FIG.

[0104] In this variant, the control module 12 is intended to regulate the amplitude i of the current flowing through the main transistor Q1 to a predetermined constant value within a predetermined period of time. In other words, the pre-charging device 10 is intended to behave as a constant current source, whatever the amplitude of the current drawn by the capacitor 3. It is therefore intended to deliver the electrical energy required to pre-charge the capacitor 3 within a period of time that is neither too short (to avoid electrical overload) nor too long (to avoid unnecessary delays in starting the motor vehicle).

[0105] In this variant, the pre-charging device 10 is connected to Figure 3A The illustrated one differs only in that it comprises a parallel circuit connected on one side to the connection terminal 15 and on the other side to an electrical line connecting the two transistors Q1 , Q2 together.

[0106] The parallel circuit includes a resistor R6 and a Zener diode D3 connected in parallel, and the anode of the Zener diode is connected to one side of the connection terminal 15 .

[0107] This parallel circuit makes it possible to limit the amplitude i of the current delivered by the battery 2 to the capacitor 3 by using the linear mode in which the main transistor Q1 is controlled (see Figure 4C ). A linear increase in the voltage across the terminals of capacitor 3 is thus observed.

[0108] In this variant, the amplitude of the current does not have a peak value, but is regulated, which allows reducing the time required for pre-charging.

[0109] Figure 5A Shows Figure 3A In another variant embodiment of the pre-charging device 10, operational amplifier AO1 is used.

[0110] In this variant, Figure 5CAs shown, the control module 12 generates a constant current profile with two plateaus of amplitude i. During the first plateau, the device allows the detection of a possible short circuit. If no short circuit is detected, the device is designed to continue pre-charging with a second plateau whose amplitude is greater than that of the first plateau. Otherwise, pre-charging is interrupted. Therefore, the device ensures that its electrical components are well protected.

[0111] Figure 5B The variation of the voltage delivered to the capacitor is shown. From this figure, it can be seen that the voltage increases linearly with two different slopes.

[0112] exist Figure 5A It can be seen that the power module 14 includes three terminals V0, V DD , star circuit of HV+.

[0113] The terminal V0 is connected to the negative power supply pin of the operational amplifier AO1 and the connection terminal 16 of the pre-charging device 10 .

[0114] Terminal V DD Connect to the positive supply pin of operational amplifier AO1.

[0115] The terminal HV+ is connected to the connection terminal 15 of the pre-charging device 10 .

[0116] The star circuit has a central connection point.

[0117] The star circuit comprises a parallel RC circuit between the central connection point and the terminal V0, the circuit comprising a capacitor C13 and a resistor R20.

[0118] The star circuit consists of a central connection point with terminals V DD between the resistor R21.

[0119] Finally, the star circuit comprises a MOSFET-type transistor Q12 between the central connection point and the terminal HV+, the gate of which is connected to the terminal V0 via a Zener diode D11 and to the terminal HV+ via a resistor R19 .

[0120] The control module 12 for its part comprises a short-circuit detection circuit SCD1 which is suitable for measuring the voltage at the terminal HV+ and for deducing therefrom the presence or absence of a short circuit.

[0121] The control module comprises a pattern generation circuit PG1 at the output of the short-circuit detection circuit SCD1 , the pattern generation circuit being adapted to deliver to its output a voltage signal having a plurality of plateaus (in the event that a short-circuit is not detected).

[0122] The control module 12 further includes the aforementioned operational amplifier AO1 .

[0123] The non-inverting input terminal of the operational amplifier AO1 is connected to the output terminal of the pattern generating circuit PG1 via the resistor R11.

[0124] The operational amplifier comprises an output terminal connected to the gate of the main transistor Q1 via a resistor R13.

[0125] The operational amplifier includes an inverting input terminal connected to the main line L1 via a resistor R12 between the source of the main transistor Q1 and a shunt resistor R10 provided on the main line L1.

[0126] The control module 12 further includes a parallel RC circuit including a resistor R12 and a capacitor C12 connected between the inverting input terminal and the output terminal of the operational amplifier AO1 .

[0127] Finally, the control module comprises a resistor R15 connected between the connection terminal 16 and the gate of the main transistor Q1 .

[0128] Figure 6 A second embodiment of the invention is shown, in which the main transistor Q3 is a MOSFET type transistor.

[0129] In this embodiment, the control module 12 comprises an integrated circuit P1 suitable for controlling the main transistor Q3 in pulse width modulation (PWM) mode (ie no longer in linear mode but in ON / OFF switching mode).

[0130] The controller here is a current mode controller of type UN3842.

[0131] The controller here includes four inputs, namely:

[0132] - connected to the power input E1 of the power module 14,

[0133] - Clock input E2, consisting of resistor R8 and capacitor C5, which generates a signal with a frequency greater than 100kHz,

[0134] - a ground input E3, which is connected to the connection terminal 15, and

[0135] A measuring input E4 connected to the main line L1 between the connection terminal 15 and the main transistor Q3 .

[0136] It will be observed here that a shunt resistor R7 (of very low resistance) is provided between the connection terminal 15 and the connection point of the measurement input E4 on the main line L1 , which allows the controller to measure the amplitude i of the current flowing through the main line L1 .

[0137] In this embodiment, the power supply module 14 comprises a voltage regulator consisting of a resistor R9 and a Zener diode D4, which is connected on one side to the connection terminal 16 and on the other side to the connection terminal 15; this allows a regulated voltage to be ensured on the power supply input E1. The power supply module also comprises a capacitor C4 which here also makes it possible to maintain the power supply to the control module 12 during pre-charging.

[0138] The controller comprises a single output S1 connected to the gate of the main transistor Q3 to control the main transistor in a pulse width modulation (PWM) mode.

[0139] In this embodiment, the main transistor Q3 is therefore operated only in switching mode, so that the size of the selected transistor can be small.

[0140] It can be seen that the coil B1 is arranged here on the main line L1 on the side of the connection terminal 16 with respect to the main transistor Q3 , which allows smoothing of the current received by the capacitor 3 .

[0141] The invention is in no way limited to the embodiments described and shown, and a person skilled in the art will be able to add thereto any variant according to the invention.

[0142] In particular, provision may be made to use a circuit which allows the amplitude i of the current flowing through the main line L1 to be modulated such that it has a first value during a first period of time and then a second value during a second period of time which is at least three times the first value.

[0143] In this way, during a first time period, the electronic controller will be able to use a low amplitude current (e.g. 100 mA) to fully safely ensure that no short circuit affects capacitor 3. Then, during a second time period, if no short circuit is detected, the computer will be able to command capacitor 3 to be pre-charged with a higher amplitude current (e.g. 5 A).

Claims

1. A precharging device (10) for precharging a power network (1), the precharging device comprising: - a power supply line (L1) for supplying power to the power network (1), the power supply line comprising a main transistor (Q1), a control module (12) for controlling the main transistor (Q1), the control module being suitable for limiting the amplitude (i) of the current flowing through the power supply line (L1), and - a power supply module (14) for supplying power to the control module (12), the power supply module being connected to the power supply line (L1) on both sides of the main transistor (Q1).

2. The pre-charging device (10) as described in claim 1 further includes a housing (11) and two connecting terminals (15, 16) extending just from the housing (11), and the two connecting terminals (15, 16) are connected to the power supply line (L1) on both sides of the main transistor (Q1).

3. The pre-charging device (10) according to claim 1, wherein: The power module (14) is suitable for delaying the activation of the control module (12) relative to the moment when a potential difference appears across the terminals of the main transistor (Q1).

4. The pre-charging device (10) according to any one of claims 1 to 3, wherein: The control module (12) comprises exactly one transistor (Q2) connected to the main transistor (Q1), and wherein the power module (14) and the control module (12) are designed to control the main transistor (Q1) in a linear mode during pre-charging of the power network (1).

5. The pre-charging device (10) according to claim 4, wherein: The power module (14) is adapted to generate current pulses.

6. The pre-charging device (10) according to claim 4, wherein: The control module (12) is adapted to adjust the amplitude (i) of the current flowing through the main transistor (Q1) to a predetermined value within a predetermined time period.

7. The pre-charging device (10) according to any one of claims 1 to 3, wherein: The control module (12) comprises an integrated circuit (P1) suitable for controlling the main transistor (Q1) in pulse width modulation mode during pre-charging of the power network (1).

8. The pre-charging device (10) according to claim 7, wherein: The power supply line (L1) includes a coil (B1).

9. The pre-charging device (10) according to any one of claims 1 to 3, wherein: The control module (12) includes an operational amplifier.

10. The pre-charging device (10) according to any one of claims 1 to 3, wherein: The control module (12) is adapted to modulate the current amplitude (i) during pre-charging of the power network (1) to a first value during a first time period and then to a second value during a second time period, the second value being at least three times the first value.

11. The pre-charging device (10) according to any one of claims 1 to 3, wherein: The control module (12) includes a pulse width modulation circuit.

12. A power network (1), comprising: - a battery (2), - capacitor (3), - two main connecting lines (4, 6) connecting the terminals of the battery (2) to the terminals of the capacitor (3), and at least one of the main connecting lines comprising a main relay (5, 7), A precharging circuit (8) which is connected in parallel with one of the two main connecting lines (4) and comprises a precharging relay (9) and a precharging device (10) according to any one of claims 1 to 11.

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