Charging system, voltage converter unit, and storage unit

Abstract

The invention relates to a charging system (2) for a storage device (48) in an electric vehicle, comprising a voltage converter unit (3) and a storage unit (4), the storage unit (4) being designed to supply electrical energy via two supply terminals (44, 45), the storage device (48) of the storage unit (4) comprising two terminals (481, 482), the voltage converter unit (3) is designed as a separate structural unit from the storage unit (4) and is connected to the storage unit (4) by means of three terminals (31, 32, 33), said three terminals (31, 32, 33) being connected to the storage unit (4) in a disconnectable manner by means of a second and a third disconnect switch (46, 47) to the storage device supply terminals (44, 45), and the voltage converter unit (3) is designed as a separate structural unit from the storage unit (4) and is connected to the storage unit (4) by means of a second and a third disconnect switch (46, 47). And in the connected state in the storage unit (4): two of the three terminals (32, 33) are connected to two terminals (481, 482) of the storage device (48), and a third of the three terminals (31) is connected to one of the supply terminals (44, 45), and in the voltage converter unit (3), the third of the three terminals (31) is led out via a first disconnect switch (36). The voltage converter unit (3) comprises a first voltage converter (37) and a second voltage converter (57).

Description

Technical Field

[0001] The present invention relates to the field of charging systems for electrical energy storage devices, in particular mobile electrical energy storage devices, especially for electric vehicles. Background Art

[0002] Known charging devices, in particular for electric vehicles, are usually connected between a charging station and an electrical energy storage device. They serve to adjust the voltage of the charging station to the voltage level of the energy storage device as required. This is in relation to the voltage of the charging station: either the voltage at the input of the charging device is switched to the energy storage device (bypass mode) without voltage conversion, or it must be converted by a converter to a voltage that matches the voltage level of the energy storage device. Such charging devices may be subject to regulations according to which the energy storage device must be disconnectable from the charging station in an all-pole manner by means of a mechanical disconnect switch.

[0003] In known charging devices, there is a voltage converter unit which is connected between the charging station and the energy storage device, usually a rechargeable battery or accumulator. In bypass operation, rapid charging processes can be carried out, in which relatively high currents are generated, so that the line cross-sections in the voltage converter unit need to be designed to be correspondingly large. In addition, for all-pole disconnection, a plurality of disconnect switches need to be present in the voltage converter unit. In addition, with a modular design that selectively has or does not have a voltage converter unit, unnecessary duplication of components may occur. Summary of the invention

[0004] It is therefore an object of the present invention to provide a charging system, a voltage converter unit and a storage unit of the initially mentioned type which overcome the aforementioned disadvantages and which can be connected to different types of charging stations for the charging process.

[0005] At least one of these objects is achieved by a charging system, a voltage converter unit and a storage unit having the features of the respective independent claims.

[0006] Thereby, the storage device and the voltage converter arranged in the voltage converter unit can be disconnected from the storage device supply terminals in an all-pole manner by means of the three disconnect switches.

[0007] Furthermore, because there is an additional disconnect switch in the storage unit, the voltage converter unit can be equipped with only a single disconnect switch or even no disconnect switch, and since the voltage converter unit is not connected directly to the charging station but is connected to the charging station via the storage unit, disconnection of the voltage converter unit from the charging station can be achieved in the storage unit via the disconnect switch.

[0008] It is also possible to connect the storage unit directly to the first charging station via the two storage device supply terminals without having to lead the lines therefor through the voltage converter unit. In this way, the high currents generated by the rapid charging in bypass mode do not need to be led through the voltage converter unit, and the lines in the voltage converter unit 3 can be designed to be correspondingly smaller.

[0009] It is also possible to design and operate a storage unit completely without a voltage converter unit. Here, the two storage device supply terminals of the storage unit can be applied and operated in an unchanged manner, just like the supply lines for connecting to the first charging station. Thus, starting from the same storage unit, a configuration with or without a voltage converter unit can be realized. This is advantageous during manufacturing, because the storage unit can be applied to both configurations in an unchanged manner. In addition, the storage unit or the vehicle containing the storage unit can also be retrofitted with a voltage converter unit after starting operation. The voltage converter unit may be present or absent as a module. Such a module contains only a single disconnect switch or even no disconnect switch. As a result, the total number of disconnect switches is minimized.

[0010] The charging system has a first voltage converter and a second voltage converter. This allows a free selection between the two voltage converters depending on the type of charging station that can be used for the charging process.

[0011] In an embodiment, the charging system is designed according to at least one of claims 2 , 3 , 4 , 5 , 6 , 7 .

[0012] In an embodiment, the charging system is designed according to claim 8. Thereby, the charging system can be manufactured in the form of separate modules (i.e., the voltage converter unit and the storage unit) and used in combination. In particular, the charging system modularized in this way can be selectively operated with or without the voltage converter unit.

[0013] In an embodiment, the charging system is designed according to claim 9, whereby a connection between the voltage converter unit and the storage unit can be established and disconnected in a simple manner.

[0014] In an exemplary embodiment, the charging system is designed according to claim 10. As a result, the charging system can be operated with conventional locking systems in electric vehicle technology (eg interlock or HV interlock) or with guide contacts.

[0015] In an embodiment, the charging system is designed according to claim 11 and / or claim 12. Thus, the charging system is suitable for electric vehicles. The voltage suitable for the charging system may be, for example, 400 volts or 800 volts.

[0016] The voltage converter unit is designed according to claim 13. Thereby, the first input terminal can be disconnected from the first voltage converter of the voltage converter unit by means of the first disconnect switch.

[0017] The memory cell is designed according to claim 14. As a result, the memory cell can be operated selectively with or without the voltage converter unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The subject matter of the invention will be described in more detail below by means of preferred embodiments shown in the accompanying drawings. In each case, schematically shown:

[0019] Figure 1 A charging system with a voltage converter unit and a storage unit according to a first embodiment, wherein the voltage converter unit has only a first voltage converter.

[0020] Figure 2 To have Figure 1 A charging system of a first specific embodiment of a voltage converter unit.

[0021] Figure 3 A charging system having a voltage converter unit and a storage unit according to a second embodiment, wherein the voltage converter unit has only a first voltage converter therein.

[0022] Figure 4 To have Figure 3 A charging system of a second specific embodiment of a voltage converter unit.

[0023] Figure 5 According to the charging system of the present invention, Figure 1 The charging system corresponds to that of , but has two voltage converters in the voltage converter unit.

[0024] Figure 6 To have Figure 5 A charging system of a first specific embodiment of a voltage converter unit.

[0025] Figure 7 is a charging system according to the present invention, which Figure 3 The charging system corresponds to that of , but has two voltage converters in the voltage converter unit.

[0026] Figure 8 To have Figure 7 A charging system of a second specific embodiment of a voltage converter unit.

[0027] Basically, in the figures, identical or functionally identical components are or will be provided with the same reference signs. DETAILED DESCRIPTION

[0028] Figure 1 A charging system 2 connected to a first charging station 1A is shown. The charging system 2 comprises a voltage converter unit 3 and a storage unit 4.

[0029] The voltage converter unit 3 includes a first input terminal 31 , an output terminal 32 , a common terminal 33 and a first voltage converter 37 for converting a first input voltage between the first input terminal 31 and the common terminal 33 into a first output voltage between the output terminal 32 and the common terminal 33 .

[0030] When the voltage converter 37 is operated, its first input voltage is equal to the output voltage of the first charging station 1A, and its first output voltage is equal to the voltage of the energy storage device 48 .

[0031] The storage unit 4 includes:

[0032] A first terminal 41 is connected to the first input terminal 31 of the voltage converter unit 3,

[0033] a second terminal 42 for connecting to the output terminal 32 of the voltage converter unit 3 and for supplying power to the first terminal 481 of the storage device 48,

[0034] a third terminal 43 for connecting to the common terminal 33 of the voltage converter unit 3 and for supplying power to the second terminal 482 of the storage device 48,

[0035] a first storage device power supply terminal 44 for connecting to a first charging terminal 11A of a first charging station 1A, and

[0036] The second storage device power supply terminal 45 is used to be connected to the second charging terminal 12A of the charging station 1A.

[0037] The first and second storage device supply terminals 44 , 45 are connected to the first charging terminal 11A and the second charging terminal 12A of the first charging station 1 via a first supply line 13 and a second supply line 14 , respectively.

[0038] In the embodiment, the two power supply conductors 13, 14 are designed as separate cables, and the two storage device power supply terminals 44, 45 are formed on separate plugs. Thus, in the case of needing to design for high charging current, the separate cable can be made not to become too heavy.

[0039] In an embodiment, the two power supply conductors 13 , 14 are designed as a common cable, and the two storage device power supply terminals 44 , 45 are formed on a common plug.

[0040] In the voltage converter unit 3

[0041] The first input terminal 31 of the voltage converter unit 3 can be disconnected from the first voltage converter 37 by means of a first disconnect switch 36 .

[0042] In storage unit 4

[0043] • a first storage device power supply terminal 44 connected to the first terminal 41 of the storage unit 4,

[0044] • the second terminal 42 of the storage unit 4 and the first terminal 481 of the storage device 48 are disconnectably connected to the first storage device supply terminal 44 via the second disconnect switch 46, and

[0045] The third terminal 43 of the storage unit 4 and the second terminal 482 of the storage device 48 are disconnectably connected to the second storage device power supply terminal 45 by means of the third disconnect switch 47 .

[0046] In an embodiment, not the first but the second storage device supply terminal 45 is connected to the first terminal 41 of the storage unit 4. In case the polarity of the storage device 48 and the first charging station 1A is the same, this corresponds to the operation of the voltage converter 37 with opposite polarity.

[0047] The storage unit 4 and in particular the storage device 48 can be equipped with a battery management system (not shown) and / or a charging control of a known type. The latter can control, for example, the charging station 1A and / or the voltage converter unit 3 via a communication connection (not shown).

[0048] In an embodiment, the storage unit 4 is part of a consumer circuit (also called a traction circuit in the case of a vehicle) or is connected to the consumer circuit. Furthermore, the storage unit 4 may comprise further disconnect switches 483, 484 for disconnecting the first and second terminals 481, 482 of the storage device 48 from the remaining elements, for example from the voltage converter unit 3 and the consumer circuit. The presence of such further disconnect switches 483, 484 for disconnecting the storage unit 4 may be specified by the standard.

[0049] The controller 100 and the communication connection (not shown) enable the control of the disconnect switches 36, 46, 47 and the voltage converter 37. By way of example, the controller 100 is shown in the voltage converter unit 3, but can also be arranged in the storage unit 4 or outside both units. Other common elements for ensuring functionality and safety, such as common elements for monitoring the storage device supply terminals 44, 45, are not shown.

[0050] In the case where the voltage provided by the first charging station 1A is not equal to the voltage required to charge the storage device 48, the charging system 2 can switch to the converter mode. At this time, the second disconnect switch 46 is opened, and the first disconnect switch 36 and the third disconnect switch 47 are closed. The voltage converter 37 is clock driven.

[0051] Here, the voltage converter converts the voltage of the first charging terminal 11A present at the input terminal 31 of the voltage converter unit 3 via the first terminal 41 of the storage unit 4 and the first storage device supply terminal 44 and the first supply line 13 to a voltage present at the output terminal 32 of the voltage converter unit 3. This voltage is present at the first terminal 481 of the storage device 48 via the second terminal 42 of the storage unit 4. The voltages mentioned are relative to the common terminal 33.

[0052] The voltage of the second charging terminal 12A is present via the second supply line 14 and the second storage device supply terminal 45 at the third terminal 43 of the storage unit 4 and thus at the common terminal 33 of the voltage converter unit 3 and at the second terminal 482 of the storage device 48 .

[0053] In the case where the voltage provided by the first charging station 1A is equal to the voltage required to charge the storage device 48, the charging system 2 can be switched to the bypass mode. At this time, the first disconnect switch 36 is opened, and the second disconnect switch 46 and the third disconnect switch 47 are closed. The first voltage converter 37 is not driven by the clock. The voltage of the charging station 1A is present at the storage device 48.

[0054] In the event that the charging system 2 is to be electrically disconnected from the charging station 1 , all three disconnect switches 36 , 46 , 47 are opened.

[0055] The storage device 48 is typically a rechargeable battery or accumulator.

[0056] Generally, the voltage converter 37 is a DC-DC converter. For example, it can be a charge pump, a boost converter, a buck converter or a combination of a boost-buck converter, or have a different topology, such as a bridge circuit to implement a DC-DC converter. The charge pump can be designed to double or multiply the voltage.

[0057] Generally speaking, in operation, the first voltage converter 37 transfers electrical energy from the first charging station 1A to the storage device 48, the first charging station 1A supplies power to the first voltage converter 37 via the first input terminal 31 and the common terminal 33, and the first voltage converter 37 supplies power to the storage device 48 via the output terminal 32 and the common terminal 33. In an embodiment, a feedback mode for transmitting energy in the opposite direction can also be implemented. To this end, an active semiconductor switch in the first voltage converter 37 can be used instead of a passive valve (diode).

[0058] Figure 2 A charging system 2 is shown in which the first voltage converter 37 is designed as a charge pump. In the variant of the charge pump shown here, the inductance L RES and the storage device capacitance CRES The first voltage converter 37 is connected in series to form a resonant oscillating circuit. The working mode of the first voltage converter 37 is described in WO2018 / 046370 A1, the content of which is fully incorporated by reference. Figure 2 Further disconnect switches 483, 484 are also shown for disconnecting the storage device 48. These may also be present in accordance with Figure 1 in the general description.

[0059] and Figure 1 and Figure 2 similar, Figure 3 and Figure 4 Each shows a charging system 2 in which the first disconnect switch 36 is not arranged in the voltage converter unit 3, but is arranged as a first disconnect switch 36b in the storage unit 4. Here, the first storage device supply terminal 44 or the second storage device supply terminal 45 of the storage unit 4 is disconnectably connected to the first terminal 41 of the storage unit 4 by the first disconnect switch 36b of the storage unit 4. Figure 3 and Figure 4 In the embodiment of FIG. 5 , there is no disconnect switch in the voltage converter unit 3 , in particular, there is no disconnect switch for disconnecting the third terminal 31 of the three terminals of the voltage converter unit 3 .

[0060] Figure 5 A charging system 2 is shown which can be connected or is connected to a first charging station 1A and / or a second charging station 1B. The charging system 2 comprises a voltage converter unit 3 and a storage unit 4.

[0061] The voltage converter unit 3 includes a first input terminal 31 , an output terminal 32 , a common terminal 33 , and a first voltage converter 37 for converting a first input voltage between the first input terminal 31 and the common terminal 33 into a first output voltage between the output terminal 32 and the common terminal 33 .

[0062] In the voltage converter unit 3

[0063] The first input terminal 31 of the voltage converter unit 3 can be disconnected from the first voltage converter 37 by means of a first disconnect switch 36 .

[0064] The voltage converter unit 3 further includes a second input terminal 51 , a third input terminal 52 , and a second voltage converter 57 for converting a second input voltage between the second input terminal 51 and the third input terminal 52 into a second output voltage between the output terminal 32 and the common terminal 33 .

[0065] The voltage converter unit 3 further comprises:

[0066] a first converter supply terminal 54 for connection to a first charging terminal 11B of a second charging station 1B, and

[0067] The second converter power supply terminal 55 is used to connect to the second charging terminal 12B of the second charging station 1B.

[0068] The second voltage converter 57 is generally an AC-DC converter. It can be a mobile electric converter, in particular an electric converter integrated into an electric vehicle. Typically, it is used for charging on a power mains with two-phase alternating current or three-phase alternating current.

[0069] Figure 6 Shows Figure 5 The charging system 2 in the embodiment of the present invention has a voltage converter unit including a first voltage converter 37 and a second voltage converter 57. The first voltage converter 37 is designed as follows Figure 2 In the variant of the charge pump shown here, the inductor L RES and the storage device capacitance C RES The first voltage converter 37 is connected in series to form a resonant oscillating circuit. The working mode of the first voltage converter 37 is described in WO2018 / 046370 A1, the content of which is fully incorporated by reference. Figure 5 and Figure 6 The charging system shown in FIG. 4 also includes a device for disconnecting the storage device 48 ( Figure 5 and Figure 6 The other disconnect switches 483, 484 (not shown) Figure 2 as shown).

[0070] and Figure 5 and Figure 6 similar, Figure 7 and Figure 8 Each shows a charging system 2 in which the first disconnect switch 36 is not arranged in the voltage converter unit 3, but is arranged as a first disconnect switch 36b in the storage unit 4. Here, the first storage device supply terminal 44 or the second storage device supply terminal 45 of the storage unit 4 is disconnectably connected to the first terminal 41 of the storage unit 4 by the first disconnect switch 36b of the storage unit 4. Figure 7 and Figure 8 In the embodiment of FIG. 5 , there is no disconnect switch in the voltage converter unit 3 , in particular, there is no disconnect switch for disconnecting the third terminal 31 of the three terminals of the voltage converter unit 3 .

Claims

1. A charging system (2), in particular for a mobile storage device (48), in particular for a storage device (48) in an electric vehicle, comprising: A voltage converter unit (3) and a storage unit (4), wherein The storage unit (4) is designed to be supplied with electrical energy via two storage device supply terminals (44, 45). The storage device (48) of the storage unit (4) comprises two terminals (481, 482), the two terminals (481, 482) being disconnectably connected to the storage device power supply terminals (44, 45) via a second disconnect switch and a third disconnect switch (46, 47), The voltage converter unit (3) is designed as a structural unit separated from the storage unit (4), and is connected to the storage unit (4) through three terminals (31, 32, 33) of the voltage converter unit (3), and is in a connected state. In the storage unit (4) • two terminals (32, 33) of the three terminals of the voltage converter unit (3) are connected to the two terminals (481, 482) of the storage device (48), and Or according to the second embodiment variation In the storage unit (4) • a third terminal (31) of the three terminals of the voltage converter unit (3) is connected to one of the storage device power supply terminals (44, 45) via a first disconnect switch (36b), Or according to the first embodiment variation In the storage unit (4) • the third terminal (31) of the three terminals of the voltage converter unit (3) is connected to one of the storage device power supply terminals (44, 45), and In the voltage converter unit (3), the third terminal (31) of the three terminals of the voltage converter unit (3) is led out through a first disconnect switch (36), It is characterized in that The voltage converter unit (3) comprises a first voltage converter (37) and a second voltage converter (57).

2. The charging system (2) according to claim 1, characterized in that: The first voltage converter (37) is a DC-DC converter that can be connected to a DC charging station (1A).

3. The charging system (2) according to claim 1 or 2, characterized in that: The second voltage converter (57) is an AC-DC converter that can be connected to an AC charging station (1B).

4. Charging system (2) according to any one of the preceding claims, The voltage converter unit (3) comprises The first input terminal (31), Output terminals (32), Common terminal (33), and The first voltage converter (37) is used to convert a first input voltage between the first input terminal (31) and the common terminal (33) into a first output voltage between the output terminal (32) and the common terminal (33). The storage unit (4) comprises a first terminal (41) for connecting to the first input terminal (31) of the voltage converter unit (3), a second terminal (42) for connecting to the first output terminal (32) of the voltage converter unit (3) and for supplying power to the first terminal (481) of the storage device (48), a third terminal (43) for connecting to the common terminal (33) of the voltage converter unit (3) and for supplying power to the second terminal (482) of the storage device (48), a first storage device power supply terminal (44) for connecting to a first charging terminal (11A) of a first charging station (1A), and The second storage device power supply terminal (45) is used to be connected to the second charging terminal (12A) of the first charging station (1A).

5. The charging system (2) according to claim 4, wherein Or according to the second embodiment variation In the storage unit (4) • the first storage device power supply terminal (44) is disconnectably connected to the first terminal (41) of the storage unit (4) via the first disconnect switch (36b), • the second terminal (42) of the storage unit (4) and the first terminal (481) of the storage device (48) are disconnectably connected to the first storage device power supply terminal (44) via the second disconnect switch (46), and • the third terminal (43) of the storage unit (4) and the second terminal (482) of the storage device (48) are disconnectably connected to the second storage device power supply terminal (45) via the third disconnect switch (47); Or according to the first embodiment variation In the voltage converter unit (3) • the first input terminal (31) of the voltage converter unit (3) can be disconnected from the voltage converter (37) by means of a first disconnect switch (36), In the storage unit (4) • the first storage device power supply terminal (44) is connected to the first terminal (41) of the storage unit (4), • the second terminal (42) of the storage unit (4) and the first terminal (481) of the storage device (48) are disconnectably connected to the first storage device power supply terminal (44) via the second disconnect switch (46), and The third terminal (43) of the storage unit (4) and the second terminal (482) of the storage device (48) are disconnectably connected to the second storage device supply terminal (45) via the third disconnect switch (47).

6. Charging system (2) according to any one of the preceding claims, The voltage converter unit (3) comprises The second input terminal (51), The third input terminal (52), a second voltage converter (57) for converting a second input voltage between the second input terminal (51) and the third input terminal (52) into a second output voltage between the output terminal (32) and the common terminal (33), The memory unit (4) comprises a first terminal (41) for connecting to the input terminal (31) of the voltage converter unit (3), a second terminal (42) for connecting to the output terminal (32) of the voltage converter unit (3) and for supplying power to the first terminal (481) of the storage device (48), a third terminal (43) for connecting to the common terminal (33) of the voltage converter unit (3) and for supplying power to the second terminal (482) of the storage device (48), a first storage device power supply terminal (44) for connecting to a first charging terminal (11A) of a first charging station (1A), and a second storage device power supply terminal (45) for connecting to a second charging terminal (12A) of the first charging station (1A); in Or according to the second embodiment variation In the storage unit (4) • the first storage device power supply terminal (44) is disconnectably connected to the first terminal (41) of the storage unit (4) via the first disconnect switch (36b), • the second terminal (42) of the storage unit (4) and the first terminal (481) of the storage device (48) are disconnectably connected to the first storage device power supply terminal (44) via the second disconnect switch (46), and • the third terminal (43) of the storage unit (4) and the second terminal (482) of the storage device (48) are disconnectably connected to the second storage device power supply terminal (45) via the third disconnect switch (47); Or according to the first embodiment variation In the voltage converter unit (3) • the first input terminal (31) of the voltage converter unit (3) can be disconnected from the voltage converter (37) by means of a first disconnect switch (36), In the storage unit (4) • the first storage device power supply terminal (44) is connected to the first terminal (41) of the storage unit (4), • the second terminal (42) of the storage unit (4) and the first terminal (481) of the storage device (48) are disconnectably connected to the first storage device power supply terminal (44) via the second disconnect switch (46), and The third terminal (43) of the storage unit (4) and the second terminal (482) of the storage device (48) are disconnectably connected to the second storage device supply terminal (45) via the third disconnect switch (47).

7. The charging system (2) according to any of the preceding claims, wherein the voltage converter unit (3) comprises a first converter supply terminal (54) for connecting to a first charging terminal (11B) of a second charging station (1B), and A second converter power supply terminal (55), the second converter power supply terminal (55) is used to connect to a second charging terminal (12) of the second charging station (1B).

8. The charging system (2) according to any of the preceding claims, wherein the voltage converter unit (3) is designed to be able to be manufactured, handled and transported independently of the storage unit (4).

9. Charging system (2) according to any of the preceding claims, wherein the three terminals (31, 32, 33) connecting the voltage converter unit (3) to the storage unit (4) are disconnectable and reconnectable terminals, in particular plug-in terminals or screw terminals or clamping terminals.

10. The charging system (2) according to any one of the preceding claims, wherein: The storage device power supply terminals (44, 45) are formed on a single plug or two separate plugs, wherein in particular the single plug or the two plugs each have a safety contact for a guide circuit or a safety circuit.

11. The charging system (2) according to any of the preceding claims, wherein the storage device supply terminals (44, 45) are designed for a maximum fast charging current which is more than twice the maximum charging current that the voltage converter unit (3) can provide.

12. The charging system (2) according to any one of the preceding claims, wherein: The storage device supply terminals (44, 45) are designed for a maximum fast charging current of more than 300 amperes, in particular more than 400 amperes, and / or the voltage converter unit (3) is designed for a maximum charging current of more than 50 amperes, in particular more than 100 amperes.

13. A voltage converter unit (3), in particular for a charging system (2) according to any one of claims 1 to 12, comprising A first input terminal (31) is used to connect to a first pole of an input voltage source, An output terminal (32) is used to connect to a first pole of an electrical device to be powered, and a common terminal (33) for connecting to the second pole of the input voltage source and the second pole of the power consumption device, in, The input terminal (31) is led out through a first disconnect switch (36).

14. A storage unit (4), in particular for use in a charging system (2) according to any one of claims 1 to 12, comprising two storage device power supply terminals (44, 45) and a storage device (48), in, The storage device (48) comprises two terminals (481, 482), the two terminals (481, 482) being disconnectably connected to the storage device power supply terminals (44, 45) via a second disconnect switch and a third disconnect switch (46, 47), The storage unit (4) comprises three terminals (41, 42, 43), wherein the three terminals (41, 42, 43) are used to be connected to corresponding terminals of the voltage converter unit (3), and In the storage unit (4) • two of the three terminals (42, 43) are connected to the two terminals (481, 482) of the storage device (48), Or according to the second embodiment variation • a third terminal (41) of the three terminals is disconnectably connected to one of the storage device power supply terminals (44, 45) via a first disconnect switch (36b), Or according to the first embodiment variation • The third terminal (41) of the three terminals is connected to one of the storage device power supply terminals (44, 45).

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