Power supply system for vehicle

Abstract

The invention relates to an electric power supply system (1) for an electric or hybrid vehicle comprising an electric power supply bus (HV), said system (1) comprising: a) a DC-DC voltage converter (50); b) at least two power supply units (10, 20, 30), each power supply unit comprising i. Rectifiers (r1, r2, r3), ii. Batteries (B1, B2, B3) connected to the rectifiers (r1, r2, r3), and iii. Switching units (C10, C20, C30) comprising switches (I10, I10 ', I20, I20', I30, I30 ') capable of connecting the batteries (B1, B2, B3) to the converter (50); c) a first group of switches (I3) capable of connecting the cells (B1, B2, B3) in series; d) a second set of switches (I4) capable of connecting all the batteries (B1, B2, B3) connected in series to the power supply bus (HV); e) a control unit configured to control all the switches (I3, I4, I10, I10 ', I20, I20', I30, I30 ').

Description

Field of the Invention

[0001] The present invention relates to the field of hybrid or electric vehicles, and more particularly to an electrical power supply system for a hybrid or electric vehicle. Background Art

[0002] As is well known, an electric or hybrid vehicle includes an electric motor for propelling the vehicle and a "traction" battery that can be connected to the electric motor or other devices. An inverter (especially a "traction" inverter) is connected between the battery and the electric motor and enables the conversion of the DC voltage provided by the battery into a three-phase AC voltage in order to supply each phase of the electric motor.

[0003] The vehicle also includes an internal electrical power supply network that enables the supply of electrical power to the vehicle's electrical devices (such as windshield wipers, headlights, dashboard warning lights, etc.). More precisely, the vehicle includes a "low-voltage" network and a "high-voltage" network.

[0004] The voltage provided by the low-voltage network is, for example, 12 or 14 volts.

[0005] The vehicle also includes an auxiliary battery and a DC-DC voltage converter capable of supplying power to the low-voltage electrical network. The DC-DC converter can be connected between the auxiliary battery and the traction battery in order to recharge the auxiliary battery, or it can also be connected between the traction battery and the low-voltage network in order to supply power to the low-voltage network.

[0006] The disadvantage thereof is that a large number of converters must be installed and configured in the vehicle.

[0007] In addition, both the traction battery and the auxiliary battery are actually composed of a set of battery cells that are statically connected to each other, in other words, a set of basic electrochemical battery cells. The charge level of each battery depends on the state of charge of each battery cell. However, the electrical and energy characteristics of the battery cells that make up the battery are not the same and vary over time and with their load. The size of each battery must also take into account the aging phenomenon and performance of each battery cell, which is restrictive.

[0008] In addition, the components of the converter and the inverter are dimensioned such that the voltages provided by the converter and the inverter are both limited within a wide voltage range. Therefore, since each of these components is not dimensioned for the optimal operating voltage, this may result in greater conversion losses compared to when dimensioned for the optimal operating voltage. In addition, it is also more difficult to precisely control the output voltage of each converter and / or inverter.

[0009] Therefore, a solution is needed that can at least partially overcome the above disadvantages. Summary of the Invention

[0010] To this end, the present invention relates to an electrical power supply system for an electric or hybrid vehicle, the vehicle comprising an electrical power supply bus capable of supplying electrical power to electrical equipment installed in the vehicle, the system comprising:

[0011] a) a DC-DC voltage converter,

[0012] b) at least two power supply units, each power supply unit comprising:

[0013] i. a rectifier capable of providing an alternating voltage based on a direct current voltage and vice versa,

[0014] ii. a battery electrically connected to the rectifier, the battery being capable of operating in a discharge mode in which the battery can provide a direct current voltage and capable of operating in a charging mode in which the battery can be recharged based on a direct current voltage,

[0015] iii. a switch unit comprising a switch capable of connecting the battery to the converter,

[0016] c) a first set of switches capable of connecting the batteries of the power supply units to the batteries of adjacent power supply units in order to connect the batteries in series,

[0017] d) a second set of switches capable of connecting all the batteries connected in series to the electrical power supply bus,

[0018] e) a control unit configured to control each switch of the first set of switches, the second set of switches and each switch unit.

[0019] Thus, the present invention relates to an electrical power supply system capable of supplying electrical power to the electrical power supply bus via a DC-DC voltage converter connected to a battery included in one of the power supply units. In addition, the electrical power supply system also enables electrical power to be supplied to an electrical device connected to the rectifier by means of the electrical power provided by the electrical power supply bus via the power supply unit. Thus, the electrical power supply system is advantageously bi-directional.

[0020] Preferably, the electrical power supply system is configured to operate in a first operating mode in which:

[0021] a) the rectifier of each power supply unit is connected to an alternating voltage,

[0022] b) the DC-DC converter is connected on the one hand to one of the power supply units and on the other hand to the electrical power supply bus in order to supply electrical energy to the electrical power supply bus.

[0023] Thus, if a voltage is applied at the input of each power supply unit, in other words, if the battery of each power supply unit is operating in the charging mode, it is possible to simultaneously supply power to the power supply bus via the DC-DC voltage converter and recharge the batteries of one or more power supply units not connected to the DC-DC converter. Additionally, the power supply system is configured to alternate the batteries connected to the DC-DC converter. Thus, this makes it possible to maintain a balanced state of charge between each battery of each power supply unit.

[0024] Also preferably, the power supply system includes a connection module that can electrically connect each power supply unit to a power supply network capable of providing an AC voltage or an electrical device external to the vehicle that can be powered based on the AC voltage:

[0025] a) If the AC voltage provided by the power supply network or if the voltage required to power the electrical device is single-phase, the connection module can connect the single-phase voltage to at least one power supply unit,

[0026] b) If the AC voltage provided by the power supply network or if the voltage required to power the electrical device is three-phase, the connection module can connect each phase of the voltage to the power supply unit.

[0027] Therefore, the power supply system not only makes it possible to supply power to each power supply unit and thus to each battery, but also makes it possible to supply power to the power supply bus based on a single-phase or three-phase voltage via the DC-DC converter.

[0028] Advantageously, when the power supply system is operating in the first operating mode:

[0029] a) The first set of switches and the second set of switches are open,

[0030] b) The switch of the switch unit of one of the power supply units is closed to connect the power supply unit to the DC-DC converter.

[0031] Therefore, since each battery is isolated from the other batteries, it makes it possible to give each of the batteries a different function: one of the batteries is connected to the DC-DC converter, and one or more other batteries are recharged with electrical energy.

[0032] Preferably, each power supply unit includes a coil connected to the input of the rectifier. Each coil makes it possible to control the current by adjusting the voltage across each battery.

[0033] Also preferably, the power supply system includes three power supply units. For a three-phase AC voltage, it is common and necessary that each phase of the AC voltage has a power supply unit.

[0034] Advantageously, the connection module comprises:

[0035] a. A first connection terminal electrically connected to the first power supply unit,

[0036] b. A second connection terminal,

[0037] c. A third connection terminal,

[0038] d. A first switch capable of connecting the second power supply unit to the first connection terminal or the second connection terminal,

[0039] e. A second switch capable of connecting the third power supply unit to the first connection terminal or the third connection terminal.

[0040] Thus, if the voltage provided at the first connection terminal is single-phase and powers the first power supply unit, said voltage can also power the second and third power supply units. Additionally, if the voltage provided at the first connection terminal is three-phase: each phase is connected to a connection terminal which is itself connected to a power supply unit. Thus, the charging of the battery is simultaneous with the powering of the power supply bus based on single-phase or three-phase voltage.

[0041] The invention also relates to a motor vehicle comprising a power supply bus capable of powering electrical equipment installed in the vehicle, and a power supply system as described above.

[0042] The invention also relates to a method for controlling an electrical system as described above, said method being implemented by a control unit and comprising the following steps:

[0043] a) Connecting the rectifier of each power supply unit to an alternating voltage,

[0044] b) Connecting the DC-DC converter on the one hand to one of the power supply units and on the other hand to the power supply bus in order to supply electrical energy to the power supply bus.

[0045] Thus, for the voltage applied at the input of each power supply unit, the method makes it possible to simultaneously supply power from the battery to the power supply bus via the DC-DC converter and to recharge one or more other batteries. The method is easy to implement since it is done by controlling the opening or closing of certain switches. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Other features and advantages of the invention will also become apparent by reading the following description. This is purely illustrative and should be read in conjunction with the accompanying drawings, in which:

[0047] Figure 1 Is a circuit diagram of a power supply system according to the invention.

[0048] Figure 2 Circuit diagram showing a first operating mode of a power supply system according to Figure 1 .

[0049] Figure 3 Circuit diagram showing a second operating mode of a power supply system according to Figure 1 . DETAILED DESCRIPTION

[0050] Vehicle

[0051] A vehicle according to the present invention will now be described with reference to Figure 1 . The vehicle particularly includes a high - voltage power supply bus HV. The high - voltage power supply bus HV is capable of supplying electrical energy to various electrical devices installed in the vehicle. Even more precisely, the high - voltage power supply bus includes a positive terminal HV+ and a negative terminal HV-.

[0052] The vehicle further includes a power supply system 1.

[0053] Power supply system

[0054] Referring to Figure 1 , the power supply system 1 includes at least two power supply units 10, 20, 30, a connection module 40, a DC - DC voltage converter 50, and a control unit (not shown in the figure).

[0055] The DC - DC converter 50 is intended to be electrically connected between the positive terminal HV+ and the negative terminal HV- of the power supply bus.

[0056] Preferably, the power supply system 1 includes a first power supply unit 10, a second power supply unit 20, and a third power supply unit 30. Each power supply unit 10, 20, 30 is capable of converting an AC voltage into a DC voltage.

[0057] Power supply units 10, 20, 30

[0058] Each power supply unit 10, 20, 30 includes: rectifiers r1, r2, r3; batteries B1, B2, B3; and a switch unit C 10 , C 20 , C 30 .

[0059] More precisely, the rectifiers r1, r2, r3 of each power supply unit 10, 20, 30 are bidirectional. In other words, each rectifier r1, r2, r3 is capable of providing an AC voltage based on a DC voltage and vice versa. The rectifier is also referred to as a "full - wave" rectifier.

[0060] Each rectifier r1, r2, r3 includes two input terminals and two output terminals.

[0061] More precisely, in the present case, each rectifier r1, r2, r3 includes a first switch connected between the high point PH and the first midpoint PM1, a second switch connected between the first midpoint PM1 and the low point PB, a third switch connected between the high point PH and the second midpoint PM2, and a fourth switch connected between the second midpoint PM2 and the low point PB. The two input terminals of each rectifier r1, r2, r3 designate the first midpoint PM1 and the second midpoint PM2. The two output terminals designate the high point PH and the low point PB.

[0062] The batteries B1, B2, B3 of each power supply unit 10, 20, 30 are capable of operating in a discharge mode, in which the batteries B1, B2, B3 are capable of supplying a DC voltage. In addition, the value of the DC voltage supplied by each battery B1, B2, B3 is controllable. In addition, the batteries B1, B2, B3 of each power supply unit 10, 20, 30 are also capable of operating in a charging mode, in which the batteries B1, B2, B3 are recharged.

[0063] In addition, the batteries B1, B2, B3 of each power supply unit 10, 20, 30 are connected to the respective rectifiers r1, r2, r3. More precisely, each battery B1, B2, B3 is connected between the two output terminals of the respective rectifier r1, r2, r3.

[0064] The switch units C 10 , C 20 , C 30 of each power supply unit 10, 20, 30 are capable of connecting the batteries B1, B2, B3 to the DC-DC converter 50. In other words, the switch units C 10 , C 20 , C 30 are connected on the one hand to the batteries B1, B2, B3 and on the other hand to the DC-DC converter 50.

[0065] Each switch unit C 10 , C 20 , C 30 includes a first switch I10, I20, I30 and a second switch I10', I20', I30'.

[0066] The first switches I10, I20, I30 of each power supply unit 10, 20, 30 make it possible to connect the first terminals of the batteries B1, B2, B3 to the terminals of the DC-DC converter 50.

[0067] The second switches I10', I20', I30' of each power supply unit 10, 20, 30 make it possible to connect the second terminals of the batteries B1, B2, B3 to the second terminals of the DC-DC converter 50.

[0068] Coil

[0069] In addition, each power supply unit 10, 20, 30 includes coils L1, L2, L3 connected to the inputs of rectifiers r1, r2, r3; in other words, the coils are connected to the rectifiers r1, r2, r3 on the one hand and to the AC voltage on the other hand.

[0070] The power supply system 1 further includes a first set of switches I3 and a second set of switches I4.

[0071] First group of switches I3

[0072] The first set of switches I3 is capable of connecting the batteries B1, B2, B3 of the power supply units 10, 20, 30 to the batteries B1, B2, B3 of adjacent power supply units 10, 20, 30 in order to connect the batteries B1, B2, B3 in series.

[0073] To this end, the first set of switches I3 includes:

[0074] a. A switch connected to the battery B1 of the first power supply unit C on the one hand and to the battery B2 of the second power supply unit C on the other hand, 10 and to the battery B2 of the second power supply unit C 20 on the other hand.

[0075] b. A switch connected to the battery B2 of the second power supply unit C on the one hand and to the battery B3 of the third power supply unit C on the other hand. 20 and to the battery B3 of the third power supply unit C 30 on the other hand.

[0076] Thus, the batteries B1, B2, B3 can be connected in series; it is said that these batteries form a power supply branch.

[0077] Second group of switches I4

[0078] The second set of switches I4 enables the battery B1 of the first power supply unit C 10 to be connected to the power supply bus HV, in particular in order to connect the branch of the batteries B1, B2, B3 connected in series between the positive terminal HV+ and the negative terminal HV- of the power supply bus HV.

[0079] Connection module 40

[0080] The connection module 40 is capable of being connected to an electrical device outside the power supply network or the vehicle on the one hand and to at least one of the power supply units 10, 20, 30 on the other hand.

[0081] When the connection module 40 is connected to the power supply network, the power supply network enables the recharging of at least one of the batteries B1, B2, B3 of at least one of the power supply units 10, 20, 30 connected to the connection module 40.

[0082] When the connection module 40 is connected to an electrical device, at least one of the batteries B1, B2, B3 of at least one of the power supply units 10, 20, 30 connected to the connection module 40 enables the power supply of the device.

[0083] More precisely, if the alternating voltage provided by the power supply network or the voltage required to supply power to the electrical device is single-phase, the connection module 40 is capable of connecting the single-phase voltage to at least one of the power supply units 10, 20, 30. If the alternating voltage provided by the power supply network or if the voltage required to supply power to the electrical device is three-phase, the connection module 40 is capable of connecting each phase of the alternating voltage to its own power supply unit 10, 20, 30.

[0084] Even more precisely, the connection module 40 includes a first connection terminal 41, a second connection terminal 42, and a third connection terminal 43.

[0085] When the alternating voltage provided by the power supply network or the voltage required to supply power to the electrical device is three-phase, each phase of the voltage is connected to its own connection terminal 41, 42, 43. On the contrary, when the alternating voltage provided by the power supply network or when the voltage required to supply power to the electrical device is single-phase, the phase of the voltage is connected to the first connection terminal 41.

[0086] In addition, the first connection terminal 41 is connected to the first switch unit 10, more precisely to the input terminal of the rectifier r1 of the first switch unit 10.

[0087] The connection module 40 further includes:

[0088] a) A first switch I5, which is configured to:

[0089] i) In the first position: connect the first connection terminal 41 to the second power supply unit 20, and more precisely to the input terminal of the rectifier r2 of the second power supply unit 20,

[0090] ii) In the second position: connect the second connection terminal 42 to the second power supply unit 20, and more precisely to the input terminal of the rectifier r2 of the second power supply unit 20,

[0091] b) A second switch I6, which is configured to:

[0092] i) In the first position: Connect the first connection terminal 41 to the third power supply unit 30, and more precisely to the input terminal of the rectifier r3 of the third power supply unit 30.

[0093] ii) In the second position: Especially when the alternating voltage provided by the power supply network or the voltage required to supply an electrical device is three-phase, connect the third connection terminal 43 to the third power supply unit 30, and more precisely to the input terminal of the rectifier r3 of the third power supply unit 30.

[0094] Furthermore, the connection module 40 is also connected to the neutral line of the alternating voltage, and the connection module 40 is configured to connect the neutral line to the second input terminal of each rectifier r1, r2, r3.

[0095] In addition, each power supply unit 10, 20, 30 may further include an EMC filter (EMC stands for "electromagnetic compatibility"), which is connected between each rectifier r1, r2, r3 and the connection module 40, and more precisely between the coils L1, L2, L3 and the connection module 40.

[0096] The control unit (not shown in the figure) is configured to control the switches I5, I6 of the connection module 40, the first group of switches I3, the second group of switches I4, and each switch unit C 10 , C 20 , C 30 and the opening and closing of each switch I10, I10', I20, I20', I30, I30' of each rectifier r1, r2, r3. The control unit is also capable of controlling the voltage provided and generated by each battery B1, B2, B3 in order to, for example, regulate the current in the inductors L1, L2, L3 or the voltage to be supplied to the DC-DC converter 50.

[0097] Operating modes

[0098] Now, several operating modes of the power supply system 1 described above will be described with reference to Figure 2 Recall that the control unit has the task of controlling each switch in order to implement the following operating modes.

[0099] First, the first and second operating modes of connecting a three-phase electrical network to the connection module will be described. In this case, each phase of the voltage provided by the network is connected to its own connection terminal 41, 42, 43 (and thus to its own power supply unit 10, 20, 30), and the first switch I5 and the second switch I6 of the connection module 40 are in the second position. The first group of switches I3 and the second group of switches I4 are open, so that each battery B1, B2, B3 is not connected to the batteries B1, B2, B3 of the adjacent power supply units 10, 20, 30.

[0100] According to the first operating mode of reference Figure 2 , each power supply unit C 10 , C 20 , C 30 is powered by one phase of the electrical network, so that each battery B1, B2, B3 can be recharged.

[0101] According to the second operating mode of reference Figure 3 , one of the power supply units 10, 20, 30 is connected to the DC-DC converter 50. According to the example described here, this is the first power supply unit 10. In other words, here, the switch units C 10 of the power supply unit 10, switches I10, I10' are closed. Therefore, this enables one phase to be connected to the first power supply unit 10, which is itself connected to the DC-DC converter 50, which is itself connected between the positive terminal HV+ and the negative terminal HV- of the power supply bus HV.

[0102] In other words, in this configuration, the battery B1 of the power supply unit 10 supplies power to the power supply bus HV via the DC-DC converter 50. The other batteries B2, B3, for which they operate in the charging mode, are charged based on the voltage provided by the AC electrical network.

[0103] Furthermore, in the case where an electrical device outside the vehicle is connected to the connection module 40, the power supply system 1 operates in a third operating mode, and the voltage required to operate the device is three-phase. According to this third configuration, each phase of the voltage is connected to its own connection terminals 41, 42, 43 (and thus to its own power supply units 10, 20, 30), and the first switch I5 and the second switch I6 of the connection module 40 are in the second position. The first set of switches I3 and the second set of switches I4 are open, so that each battery B1, B2, B3 is not connected to the batteries B1, B2, B3 of the adjacent power supply units 10, 20, 30.

[0104] Therefore, each battery B1, B2, B3 supplies power to one phase of the voltage, so that power can be supplied to the electrical device connected to the connection module 40.

[0105] Furthermore, by means of the connection module 40, the first and second operating modes of the power supply network providing single-phase voltage can also be achieved.

[0106] Therefore, the power supply system 1 enables power to be supplied from the DC-DC voltage converter 50 to the vehicle's power supply bus HV based on single-phase or three-phase voltage, while allowing the batteries of one or more power supply units 10, 20, 30 not connected to the DC-DC voltage converter 50 to be discharged to supply electrical devices or to be charged. It is also possible to change the power supply units 10, 20, 30 connected to the converter 50. Thus, it is not always the same batteries B1, B2, B3 that are discharged or charged. This makes it possible to balance the discharge levels between all the batteries B1, B2, B3 of the power supply system 1.

[0107] The control unit enables the operating mode of the power supply system to be defined.

[0108] Method

[0109] The invention also relates to a method for controlling the power supply system 1 implemented by the control unit.

[0110] For example, in order to implement the second operating mode, the control method includes the step of connecting the rectifiers r1, r2, r3 of each power supply unit 10, 20, 30 to the alternating voltage, in particular via the connection module 40.

[0111] To this end, the method also includes the step of connecting the DC-DC converter 50 on the one hand to one of the power supply units 10, 20, 30 and on the other hand to the power supply bus HV in order to supply power to the power supply bus HV. To this end, the control unit actuates the closing of the switches of the switching units C 10 、C 20 、C 30 of one of the power supply units 10, 20, 30.

Claims

1. An electrical power supply system (1) intended to be installed in an electric or hybrid vehicle, said vehicle comprising an electrical power supply bus (HV) capable of supplying electrical power to electrical equipment installed in said vehicle, said system (1) comprising: a) A DC-DC voltage converter (50), b) At least two power supply units (10, 20, 30), each power supply unit comprising: i) A rectifier (r1, r2, r3) capable of providing an alternating voltage based on a direct current voltage and vice versa, ii) A battery (B1, B2, B3), said battery being electrically connected to the rectifier (r1, r2, r3), said battery being capable of operating in a discharge mode in which the battery (B1, B2, B3) can provide a direct current voltage and being capable of operating in a charging mode in which the battery (B1, B2, B3) can be recharged based on a direct current voltage, iii) Switching unit (C 10 , C 20 , C 30 ), which includes switches (I10, I10', I20, I20', I30, I30') capable of connecting the batteries (B1, B2, B3) to the converter (50). c) A first set of switches (I3) capable of connecting the batteries (B1, B2, B3) of the power supply units (10, 20, 30) to the batteries (B1, B2, B3) of adjacent power supply units (10, 20, 30) so as to connect the batteries (B1, B2, B3) in series, d) A second set of switches (I4) capable of connecting all the batteries (B1, B2, B3) connected in series to the electrical power supply bus (HV), e) A control unit configured to control the first set of switches (I3), the second set of switches (I4), and each switch (I10, I10', I20, I20', I30, I30') of each switch unit (C 10 , C 20 , C 30 ), f) A connection module (40) capable of electrically connecting each power supply unit (10, 20, 30) to an electrical power supply network capable of providing an alternating voltage or to an electrical device external to the vehicle capable of being powered based on an alternating voltage.

2. The electrical power supply system (1) according to the preceding claim, configured to operate in a first operating mode in which: a) The rectifier (r1, r2, r3) of each power supply unit (10, 20, 30) is connected to an alternating voltage, b) The DC-DC converter (50) is connected on the one hand to one of the power supply units (10, 20, 30) and on the other hand to the electrical power supply bus (HV+, HV-) so as to supply electrical energy to the electrical power supply bus (HV+, HV-).

3. The power supply system (1) according to the preceding claim, wherein, The connection module (40) is configured to operate as follows: a) If the alternating voltage provided by the electrical power supply network or if the voltage required to supply power to the electrical device is single-phase, the connection module (40) is capable of connecting the single-phase voltage to at least one power supply unit (10, 20, 30), b) If the alternating voltage provided by the electrical power supply network or if the voltage required to supply power to the electrical device is three-phase, the connection module (40) is capable of connecting each phase of the voltage to the power supply units (10, 20, 30).

4. The power supply system (1) according to claim 2 or 3, wherein, When the electrical power supply system operates in the first operating mode: a) The first set of switches (I3) and the second set of switches (I4) are open, b) Close the switches (I10, I10', I20, I20', I30, I30') of the switch unit (C 10 , C 20 , C 30 ) of one of the power supply units (10, 20, 30) to connect the power supply unit (10, 20, 30) to the DC-DC converter (50).

5. The power supply system (1) according to any one of the preceding claims, wherein, Each power supply unit (10, 20, 30) includes coils (L1, L2, L3) connected to the rectifier (r1, r2, r3) and intended to be connected to an alternating voltage.

6. The power supply system (1) according to any one of the preceding claims, comprising three power supply units (10, 20, 30).

7. The power supply system (1) according to any one of claims 3 to 6, wherein, The connection module (40) comprises: a) a first connection terminal (41) electrically connected to the first power supply unit (10), b) a second connection terminal (42), c) a third connection terminal (43), d) a first switch (I5) capable of connecting the second power supply unit (20) to the first connection terminal (41) or the second connection terminal (42), e) a second switch (I6) capable of connecting the third power supply unit (30) to the first connection terminal (41) or the third connection terminal (43).

8. A motor vehicle, comprising a power supply bus (HV+, HV-) capable of supplying power to electrical equipment installed in the vehicle and a power supply system (1) according to any one of the preceding claims.

9. A method for controlling a system (1) according to any one of the preceding claims, the method being implemented by a control unit and comprising the following steps: a) connecting the rectifiers (r1, r2, r3) of each power supply unit (10, 20, 30) to an alternating voltage, b) connecting the DC-DC converter (50) on the one hand to one of the power supply units (10, 20, 30) and on the other hand to the power supply bus (HV+, HV-) so as to supply electrical energy to the power supply bus (HV+, HV-).

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