Low-voltage network for an electric vehicle, power supply network for an electric vehicle, and method for operating a power supply network

Abstract

The invention relates to the connection of a photovoltaic installation (3) to a power supply network (1, 2) of an electric vehicle. According to the invention, at least one sub-network of the low-voltage network (1) of the electric vehicle is configured without a dedicated electrical energy store, and the photovoltaic module (3) is connected to this part of the low-voltage network (1). As a result, the voltage level in this part of the low-voltage network (1) can be varied within a predefined value range in order to adapt the voltage level to the output voltage of the photovoltaic installation (3), thereby regulating the operating point of the photovoltaic installation (3).

Description

[0001] R. 415155

[0002] - 1 -

[0003] Description

[0004] title

[0005] Low-voltage network for an electric vehicle, power supply network for an electric vehicle and methods for operating a power supply network

[0006] Technical field

[0007] The present invention relates to a low-voltage network for an electric vehicle. The present invention further relates to a power supply network for an electric vehicle comprising such a low-voltage network, and to a method for operating such a power supply network. The present invention relates in particular to the connection of a photovoltaic module in a power supply network for an electric vehicle.

[0008] background

[0009] Vehicles that are fully or partially electrically powered generally have an electrical energy storage device, such as a traction battery. This electrical energy storage device provides the energy required to drive the electric vehicle in the form of direct current (DC). This DC voltage can be converted into single-phase or multi-phase alternating current (AC) using a suitable inverter and supplied to an electric motor. The electrical energy storage device can be recharged from an external energy source when the vehicle is stationary. For this, the vehicle must be connected to such an external energy source at a suitable charging point. However, R. 415155

[0010] - 2 - requires that the electric vehicle is parked directly at such a charging point for the charging process.

[0011] Another way to charge the electrical energy storage system of an electric vehicle is, for example, to attach one or more photovoltaic modules to the vehicle. Such photovoltaic modules can provide electrical energy when exposed to suitable sunlight, which can then be used to charge the vehicle's electrical energy storage system.

[0012] For example, German patent application DE 11 2010 000 733 T describes a photovoltaic storage and charging system for a vehicle with a photovoltaic device mounted on the vehicle. The electrical energy provided by the photovoltaic device is first stored in an intermediate storage unit and can then be converted by means of an additional voltage converter to a voltage level suitable for charging the high-voltage battery of the electric vehicle.

[0013] Disclosure of the invention

[0014] The present invention provides a low-voltage network for an electric vehicle, a power supply network for an electric vehicle, and a method for operating a power supply network for an electric vehicle, comprising the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0015] Accordingly, the following is provided: R. 415155

[0016] - 3 -

[0017] A low-voltage network for an electric vehicle with a photovoltaic connection and a first DC-DC converter. The photovoltaic connection is designed to couple the electric vehicle's low-voltage network with a photovoltaic system. The first DC-DC converter is designed to exchange electrical energy between the low-voltage network and a high-voltage network. This energy exchange between the low-voltage and high-voltage networks can be bidirectional, meaning the DC-DC converter can transfer electrical energy both from the high-voltage network to the low-voltage network and vice versa. The photovoltaic connection can be designed, in particular, to allow the electrical energy from the photovoltaic system to be fed directly into the low-voltage network without prior storage or voltage conversion.

[0018] Furthermore, the following is planned:

[0019] An energy supply network for an electric vehicle comprising a low-voltage network according to the invention, a high-voltage battery, a second DC-DC converter, and a high-voltage network. The second DC-DC converter is designed to exchange electrical energy between the low-voltage network and the high-voltage battery. The second DC-DC converter and the high-voltage battery are arranged in a common housing element. In particular, the second DC-DC converter and the high-voltage battery are arranged such that suitable contact protection is provided for the electrical connection between the second DC-DC converter and the high-voltage battery. The first DC-DC converter of the low-voltage network is connected to the high-voltage network, with the high-voltage battery and the high-voltage network being separably coupled to each other.In other words, the electrical connection between the high-voltage battery and the high-voltage network can be interrupted by means of a suitable switching element. Such a switching element is R. 415155.

[0020] - 4 - can, for example, be arranged in the housing element which also includes the high-voltage battery and the second DC-DC converter

[0021] Finally, the following is planned:

[0022] A method for operating an energy supply network, in particular an energy supply network according to the invention for an electric vehicle. The method comprises a first operating mode in which electrical energy is transferred from the low-voltage network to the high-voltage battery using the first DC-DC converter. Optionally, the second DC-DC converter can also transfer electrical energy from the low-voltage network to the high-voltage battery in parallel. The first operating mode can be executed particularly when a power flow from the photovoltaic system to the low-voltage network exceeds a predetermined first threshold. The method further comprises a second operating mode in which the first DC-DC converter is deactivated and electrical energy is transferred from the low-voltage network to the high-voltage battery using the second DC-DC converter.The second operating mode is executed, in particular, if the power flow from the photovoltaic system to the low-voltage grid falls below the predetermined first threshold but exceeds a predetermined second threshold. This second threshold could, for example, be a threshold that characterizes the electrical energy consumption of the electrical loads connected to the low-voltage grid. Furthermore, the system includes a third operating mode in which the first DC-DC converter is deactivated and electrical energy is transferred from the high-voltage battery to the low-voltage grid using the second DC-DC converter. This third operating mode is executed if the power flow from the photovoltaic system to the low-voltage grid falls below the predetermined second threshold.In particular, the third operating mode can be used if the electrical energy from the photovoltaic system is insufficient, R. 415155.

[0023] - 5 -

[0024] To cover the energy consumption of electrical consumers active in the low-voltage network.

[0025] Optionally, when an electric vehicle is parked, some of the electrical consumers connected to the low-voltage network can be deactivated. This reduces the power demand on the low-voltage network.

[0026] Advantages of the invention

[0027] The present invention is based on the understanding that the electrical systems of an electric vehicle, and in particular the low-voltage network, typically exhibit an at least approximately constant voltage. Especially when an electrical energy storage device, such as a battery or similar, is provided in the low-voltage network, the voltage in this network is determined by the battery voltage. Furthermore, the present invention is based on the understanding that the voltage provided by a photovoltaic system can fluctuate over a relatively wide voltage range, particularly with power-optimized control such as maximum power point tracking (MPPT).Therefore, conventional approaches to connecting a photovoltaic system to the power supply network of an electric vehicle currently require an additional unit that makes it possible to convert the variable electrical voltage output by the photovoltaic system to a fixed voltage level in order to feed the electrical energy from the photovoltaic system into the power supply network of the electric vehicle or directly into the traction battery.

[0028] Based on this finding, one idea of ​​the present invention is to create a concept that makes it possible to feed the electrical energy provided by the photovoltaic system into the power supply network of the electric vehicle without additional voltage conversion. For this purpose, see R. 415155.

[0029] - 6 - According to the invention, the low-voltage network of the electric vehicle is designed without an electrical energy storage device such as a battery or similar. This allows the voltage level in the low-voltage network to be varied within predefined limits and adapted to the output voltage of the photovoltaic system. In particular, the voltage level in the low-voltage network can be varied over a voltage range permissible for the operation of the electrical loads connected to the low-voltage network. In this way, optimized operation of the photovoltaic system, for example for an MPPT, is possible within this voltage range without the need for an additional voltage converter or similar device.

[0030] According to one embodiment, the low-voltage network includes a control unit. This control unit is designed to set the voltage of the low-voltage network within a predetermined range. The predetermined range can, for example, correspond to a permissible voltage range for operating the electrical loads connected to the low-voltage network. For instance, the voltage can be set between 8 and 18 volts. Depending on the application, the voltage level of the low-voltage network, and similar factors, other suitable voltage ranges are naturally possible; for example, corresponding voltage ranges for a 24-volt or a 48-volt low-voltage network are also possible.

[0031] According to one embodiment, the control unit is designed to adjust the electrical voltage of the low-voltage network based on the control of the photovoltaic system, in particular using maximum power point tracking (MPPT). When adjusting the voltage range in the low-voltage network, in addition to the requirements for the control of the photovoltaic system, the permissible voltage range for the operation of the R. 415155 connected to the low-voltage network can also be taken into account.

[0032] - 7 - electrical consumers must be taken into account. Therefore, for example, only limited MPPT operation is possible within these voltage limits.

[0033] According to one embodiment, the low-voltage network can comprise several subnetworks. The individual subnetworks can optionally be coupled to one another by means of suitable coupling or switching elements, voltage transformers, or similar devices. In particular, for example, a first subnetwork can comprise a first group of electrical loads, and a separate second subnetwork can comprise a second group of electrical loads. One subnetwork, for example the first subnetwork, can be directly connected to the photovoltaic connection.

[0034] According to one embodiment, an electrical energy storage device can be provided in the second subnetwork. The first subnetwork, on the other hand, can be implemented without an electrical energy storage device. Thus, the electrical voltage in the storage-free first subnetwork can be adjusted for the control of the connected photovoltaic system, while the electrical voltage in the second subnetwork can be stabilized by the energy storage device.

[0035] According to one embodiment, the low-voltage network includes a voltage converter connection. The voltage converter connection can be designed to be electrically coupled to a second DC-DC converter. This second DC-DC converter can be directly connected to the high-voltage battery of the electric vehicle. In particular, the second DC-DC converter can be designed to exchange electrical energy between the low-voltage network and the high-voltage battery. In this way, bidirectional energy exchange between the low-voltage network and the high-voltage battery is possible, even bypassing the high-voltage network of the electric vehicle. The second DC-DC converter can be R. 415155

[0036] - 8 - be significantly smaller than the first DC-DC converter. In particular, the second DC-DC converter can also be optimized for bidirectional power transfer or power transfer from the low-voltage network to the high-voltage battery.

[0037] The above embodiments and further developments can be combined with one another as appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0038] Brief description of the drawings

[0039] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0040] Fig. 1 : a schematic representation of a block diagram as it underlies a power supply network with a low-voltage network according to one embodiment;

[0041] Fig. 2: a schematic representation of a block diagram for a configuration of a low-voltage network according to one embodiment;

[0042] Fig. 3: a schematic representation of a block diagram such as may underlie another embodiment of a low-voltage network; and R. 415155

[0043] - 9 -

[0044] Fig. 4: a flowchart as it may form the basis of a method for operating an energy supply network according to one embodiment.

[0045] Description of embodiments

[0046] Figure 1 shows a schematic block diagram of a power supply network for an electric vehicle according to one embodiment. The power supply network comprises a low-voltage network 1 and a high-voltage network 4. Furthermore, a high-voltage battery unit 2 with a high-voltage battery 21 is provided in the power supply network, wherein the high-voltage battery 21 can comprise several battery cells. In addition, a photovoltaic system 3 can be provided. The photovoltaic system 3 is directly connected to the low-voltage network 1 via a photovoltaic connection 13.

[0047] In this context, "direct" means that the electrical energy provided by the photovoltaic modules of the photovoltaic system 3 is fed into the low-voltage network 1 without further intermediate storage or voltage conversion. Optionally, a switching device (not shown in Figure 1) may be provided which can disconnect the photovoltaic system 3 from the low-voltage network 1. This can, for example, prevent electrical energy from flowing from the low-voltage network 1 towards the photovoltaic system 3 when there is no or insufficient solar irradiance.

[0048] Various high-voltage consumers, and in particular the electric drive system with inverter and electric motor, can be connected to the high-voltage network 4. The high-voltage network 4 can, for example, be electrically coupled to the battery cells 21 of the high-voltage battery unit 2 via a suitable disconnect device 23. Thus, for example, when the electric vehicle is stationary or parked, the high-voltage network 4 can be disconnected from the high-voltage battery unit 2 and is then connected according to R. 415155.

[0049] - 10 - corresponding discharge process of the capacities in the high-voltage network 4 at least approximately voltage-free.

[0050] The high-voltage battery unit 2 can also be electrically connected to the low-voltage network 1 via the high-voltage network 4. A DC / DC converter 11 can be provided in the low-voltage network 1, which converts the electrical energy supplied by the high-voltage battery unit 2 via the high-voltage network 4 to a voltage level corresponding to the voltage level in the low-voltage network 1. In this way, for example, electrical loads 10a to 10c can be supplied with electrical energy. In contrast to conventional low-voltage networks, however, the low-voltage network 1 according to the present embodiment can be designed without storage, i.e., without an electrical energy storage device such as a low-voltage battery, supercapacitor, or similar device. Consequently, the voltage level in the low-voltage network 1 is not determined by the voltage across such an energy storage device.

[0051] In addition, the low-voltage network 1 may be provided with a further DC connection 14, through which the low-voltage network 1 can exchange electrical energy with the high-voltage battery unit 2. For this purpose, a further DC-DC converter 22 may be provided in the high-voltage battery unit 2. This further DC-DC converter 22 can, on the one hand, convert electrical energy from the battery cells 21 of the high-voltage battery unit 2 towards the low-voltage network 1, and on the other hand, also transfer electrical energy in the opposite direction from the low-voltage network 1 towards the battery cells 21 of the high-voltage battery unit 2.In this way, electrical energy can be exchanged between the low-voltage network 1 and the high-voltage battery unit 2 even if the primary DC-DC converter 11 in the low-voltage network 1, which is connected to the high-voltage network 4, is deactivated and / or the disconnecting device 23 in the high-voltage battery unit 2 is open. R. 415155.

[0052] - 11 -

[0053] Preferably, the additional DC-DC converter 22 in the high-voltage battery unit 2 is designed for a lower, in particular significantly lower, power transfer than the primary DC-DC converter 11 in the low-voltage network 1. Furthermore, the primary DC-DC converter 11 in the low-voltage network 1 can, for example, preferably be optimized for energy transfer from the high-voltage network 4 towards the low-voltage network 1, while the additional DC-DC converter 22 is optimized for bidirectional energy transfer or energy transfer from the low-voltage network 1 towards the battery cells 21 of the high-voltage battery unit 2. For example, the additional DC-DC converter 22 in the high-voltage battery unit 2 can be designed for an energy transfer of up to a maximum of 10 watts, 20 watts, 50 watts, 100 watts, 250 watts, 500 watts, or 1 kilowatt.

[0054] The additional DC-DC converter 22 can be arranged in close proximity to the battery cells 21 of the high-voltage battery unit 2. In particular, the battery cells 21 of the high-voltage battery unit 2 and the additional DC-DC converter 22 can, for example, be arranged in a common housing. Furthermore, any other suitable measures can be provided to prevent accidental contact with an electrical connection between the additional DC-DC converter 22 and the battery cells 21 of the high-voltage battery unit 2. This ensures that, for example, no electrical hazard to persons arises during maintenance of the electric vehicle. The switching element 23 for interrupting the electrical connection between the battery cells 21 and the high-voltage network 4 can also be provided in this common housing.

[0055] The following three interfaces can therefore be provided for energy exchange to and from the low-voltage network 1: Firstly, a high-voltage connection 15 can be used by means of the primary DC-DC converter 11 R. 415155

[0056] - 12 - electrical energy can be exchanged with the high-voltage network 4. In addition, electrical energy can be exchanged between the low-voltage network 1 and the further DC-DC converter 22 in the high-voltage battery unit 2 via a voltage converter connection 14. Finally, electrical energy from the photovoltaic system 3 can be fed into the low-voltage network 1 at the photovoltaic connection 13.

[0057] Due to fluctuations in solar irradiance, partial shading, or other influences, the electrical power supplied by the photovoltaic system 3 can fluctuate. The operation of the photovoltaic system 3 can be optimized by suitable control mechanisms, such as maximum power point tracking (MPPT) or similar systems. The electrical voltage supplied by the photovoltaic system 3 at the photovoltaic connection 13 can also vary. Therefore, the voltage level in the low-voltage network 1 must be adjusted accordingly. This can include, in particular, appropriate control of the DC-DC converter 11 in the low-voltage network 1 and / or the DC-DC converter 22 in the high-voltage battery unit 2.Since the low-voltage network 1, or at least a subnetwork of the low-voltage network 1 connected to the photovoltaic connection 13, is designed without electrical energy storage such as a battery or similar device, the voltage level in this network can follow the voltage required for the optimal operation of the photovoltaic system 3. The adjustment of the electrical voltage can be carried out within a predetermined voltage range. This predetermined voltage range can, for example, be defined by the maximum permissible voltage range for the electrical loads 0a to 10c connected to the low-voltage network 1. For example, the electrical voltage can be varied within a voltage range between 8 and 18 volts. To protect the electrical loads 10a to 10c in the low-voltage network 1, a further increase or decrease in the electrical voltage may not be permissible. R. 415155.

[0058] - 13 -

[0059] With the described arrangement of a low-voltage network, in particular a low-voltage network that has at least one subnetwork without energy storage such as a battery or similar device, it is thus possible to connect a photovoltaic system directly to such a low-voltage network and, by adjusting the voltage level in this section of the low-voltage network, to optimize the operation of the photovoltaic system, for example, by implementing maximum power point tracking or similar techniques. In particular, the operating strategy can be further optimized by using the additional DC-DC converter 22 in the high-voltage battery unit 2.

[0060] For example, if the photovoltaic system 3 at photovoltaic connection 13 can provide electrical power that exceeds the current consumption by consumers 10a to 10c in the low-voltage network 1, the excess electrical energy can be stored in the high-voltage battery unit 2. For this purpose, the additional DC-DC converter 22 in the high-voltage battery unit 2 can be used. In particular, this additional DC-DC converter 22 can therefore be optimized for energy transfer from the low-voltage network 1 to the battery cells 21 of the high-voltage battery unit 2. Alternatively, this additional DC-DC converter 22 can also be optimized for bidirectional energy transfer between the low-voltage network 1 and the battery cells 21 of the high-voltage battery unit 2.As previously stated, the maximum electrical power that can be exchanged between the low-voltage network 1 and the battery cells 21 of the high-voltage battery unit 2 by the additional DC-DC converter 22 can be significantly lower than the maximum power that can be converted by the primary DC-DC converter 11 in the low-voltage network 1.

[0061] As long as the photovoltaic surplus from the photovoltaic system 3 is completely converted by the further DC voltage converter 22 in the high-voltage battery unit 2 R. 415155

[0062] - 14 - can be transmitted, the primary DC-DC converter 11 in the low-voltage network 1 can be deactivated. This may also minimize the energy consumption of the primary DC-DC converter 11 when in standby mode.

[0063] However, if the photovoltaic system 3 at the photovoltaic connection 13 provides electrical power that exceeds the maximum permissible power that can be converted by the additional DC-DC converter 22 in the high-voltage battery unit 2, the electrical energy from the low-voltage network 1 to the battery cells 21 of the high-voltage battery unit 2 can also be transferred additionally or, if necessary, alternatively by the primary DC-DC converter 11 in the low-voltage network 1. If necessary, a threshold value can be specified for switching between a first operating mode, in which the primary DC-DC converter 11 in the low-voltage network 1 is active, and a second operating mode, in which the electrical power is transferred exclusively by the additional DC-DC converter 22 in the high-voltage battery unit 2.This threshold value can, for example, correspond to the maximum power output of the additional DC-DC converter 22 in the high-voltage battery unit 2. If necessary, the threshold value can also be set slightly higher to account for the energy consumption of the loads 10a to 10c in the low-voltage network 1. Alternatively, lower threshold values ​​are also possible to provide a sufficient safety margin or similar. A hysteresis function can also be provided for switching between the first and second operating modes, in order to avoid excessively frequent switching between the two operating modes, particularly under fluctuating solar irradiance.

[0064] If the electrical power supplied at photovoltaic connection 13 by the photovoltaic system 3 falls below the demand of the electrical consumers 10a to 10c in the low-voltage network 1, the additional power requirement R. 415155

[0065] - 15 - for example, by the additional DC-DC converter 22 in the high-voltage battery unit 2. Particularly when an electric vehicle is stationary, for example, parked, the power demand of the active consumers 10a to 10c can be so low that even the smaller additional DC-DC converter 22 can fully cover the power demand of consumers 10a to 10c, even if no electrical power is supplied by the photovoltaic system 3 at the photovoltaic connection 13. For this purpose, it is possible, for example, to deactivate one or more of the consumers 10a to 10c in such a standby state of the electric vehicle.

[0066] If the power demand in the low-voltage network 1 exceeds the maximum power that can be provided by the additional DC-DC converter 22 in the high-voltage battery unit 2, and if the photovoltaic system 3 at the photovoltaic connection 13 does not provide sufficient additional power, the primary DC-DC converter 11 in the low-voltage network 1 can also be activated to cover the power demand.

[0067] Figure 2 shows a schematic representation of a low-voltage network in a power supply network for an electric vehicle according to a further embodiment. The embodiment according to Figure 2 differs from the basic configuration described above, in particular in that the low-voltage network 1 includes two separate subnetworks 110 and 120. In the embodiment shown in Figure 2, the two subnetworks 110 and 120 are each connected to the high-voltage network 4 and the high-voltage battery unit 2, respectively, via separate DC-DC converters 111 and 121. Furthermore, at least the first subnetwork 110, with its photovoltaic connection 13, can optionally also be coupled to the high-voltage battery unit 2 via a further DC-DC converter 22.The first subnetwork 110 with the photovoltaic connection 13 is a low-voltage network without electrical energy storage, as previously described, so that the level of electrical voltage in this subnetwork 110 is within a range of R. 415155.

[0068] - 16 - can be varied within the specified value range. In the second subnetwork 120 of the low-voltage network 1, an electrical energy storage device 122 can be provided. Thus, the electrical voltage in this second subnetwork 120 can be maintained at the voltage level specified by the electrical energy storage device 122. The electrical energy storage device 122 can, for example, be charged with electrical energy from the high-voltage battery unit 2 via the corresponding DC-DC converter 121.

[0069] Figure 3 shows a schematic block diagram of a low-voltage network 1 for an electric vehicle power supply network according to yet another embodiment. The embodiment according to Figure 3 differs from the previously described embodiment in particular in that both the first subnetwork 110 and the second subnetwork 120 are connected to the high-voltage network 4 via a common DC-DC converter 11. A switching element 123 can, for example, be provided between the DC-DC converter 11 and the second subnetwork 120. Thus, it is possible, for example, to supply the second subnetwork 120, at least temporarily, entirely with energy from the electrical energy storage device 122.The first subnetwork 110, with the photovoltaic system 3 connected to the photovoltaic connection 13, can exchange electrical energy between the first subnetwork 110 and the high-voltage battery unit 2 via the DC-DC converter 11 and / or the additional DC-DC converter 22. Optionally, a further DC-DC converter 22 can be provided. This additional DC-DC converter 22 can connect the subnetwork 110 directly to the high-voltage battery 2, bypassing the high-voltage network 4. If the electrical energy storage device 122 in the second subnetwork 120 is to be charged, the voltage level must first be adjusted to the voltage level corresponding to the energy storage device 122. For this purpose, the control of the photovoltaic system 3 can be at least partially suspended, and optionally, the photovoltaic system 3 can be disconnected from the first subnetwork 110 by means of a suitable switching element or similar device. R. 415155.

[0070] - 17 -

[0071] Figure 4 shows a flowchart illustrating a method for operating a power supply network for an electric vehicle according to one embodiment. The method can be executed, in particular, when the vehicle is stationary, for example, parked. The method can comprise at least three operating modes. In principle, however, the method can include any steps and modes previously described in connection with the low-voltage network 1 or the power supply network for the low-voltage network 1. Similarly, the previously described low-voltage network 1 or the power supply network containing the low-voltage network can also include any components suitable for implementing the method described below.

[0072] If a high electrical power is supplied to the photovoltaic connection 13 by the photovoltaic system 3, in particular an electrical power that exceeds a predetermined first threshold, then in a first operating mode S1 the excess power in the low-voltage network 1 is transferred to the high-voltage battery unit 2 using the primary DC-DC converter 11 in the low-voltage network 1. Optionally, the additional DC-DC converter 22 in the high-voltage battery unit 2 can also transfer electrical energy from the low-voltage network 1 to the high-voltage battery unit 2, in particular to the battery cells 21 of the high-voltage battery unit 2.

[0073] If the electrical power from the photovoltaic system 3 at the photovoltaic connection 13 falls below the specified first threshold (possibly taking hysteresis into account), so that the excess power in the low-voltage network 1 can be completely transferred by the additional DC-DC converter 22 in the high-voltage battery unit 2, then in a second operating mode S2 the primary DC-DC converter 11 in the low-voltage network 1 can be deactivated and the electrical energy is transferred exclusively to the battery cells 21 of the high-voltage battery unit 2 via the additional DC-DC converter 22. R. 415155

[0074] - 18 -

[0075] If, on the other hand, the power demand in the low-voltage network 1 is higher than the electrical power that can be supplied by the photovoltaic system 3 at the photovoltaic connection 13, the additional power demand can be supplied by the high-voltage battery unit 2 in a third operating mode S3. For this purpose, the power demand can be fully supplied by the additional DC-DC converter 22 of the high-voltage battery unit 2, particularly when the electric vehicle is at rest, for example in a parked position or similar.

[0076] If necessary, individual electrical loads 10a to 10c in the low-voltage network 1 can be deactivated in the operating modes S1-S3 listed. This reduces the power demand in the low-voltage network 1 in this state.

[0077] In summary, the present invention relates to connecting a photovoltaic system to the power supply network of an electric vehicle. For this purpose, it is provided that at least one subnetwork of the electric vehicle's low-voltage network is designed without a dedicated electrical storage system and that the photovoltaic module is connected to this part of the low-voltage network. Thus, the voltage level in this part of the low-voltage network can be varied within a predetermined range in order to adapt the voltage level to the output voltage of the photovoltaic system and thereby regulate the operating point of the photovoltaic system.

Claims

R. 415155 - 19 - Claims 1. Low-voltage network (1) for an electric vehicle, comprising: a photovoltaic connection (13) designed to couple the low-voltage network (1) of the electric vehicle with a photovoltaic system (3); and a first DC-DC converter (11) designed to exchange electrical energy between the low-voltage network (1) and a high-voltage network (4).

2. Low-voltage network (1) according to claim 1, comprising a control device (19) designed to set an electrical voltage of the low-voltage network (1) within a predetermined range of values, in particular within a range between 8 volts and -18 volts.

3. Low-voltage network (1) according to claim 1 or 2, wherein the control device (19) is designed to adjust the electrical voltage of the low-voltage network (1) using maximum power point tracking.

4. Low-voltage network (1) according to one of claims 1 to 3, wherein the low-voltage network (1) comprises a first subnetwork (110) with a first group of electrical consumers and a separate second subnetwork (120) with a second group of electrical consumers, and wherein the first subnetwork (110) is directly connected to the photovoltaic connection (13).

5. Low-voltage network (1) according to claim 4, wherein the second subnetwork (120) comprises an electrical energy storage device (122). R. 415155 - 20 - 6. Low-voltage network (1) according to one of claims 1 to 5, comprising a voltage converter connection (14) designed to be electrically coupled to a second DC voltage converter (22), wherein the second DC voltage converter (22) is directly electrically coupled to a high-voltage battery (21) of the electric vehicle and is designed to exchange electrical energy between the low-voltage network (1) and the high-voltage battery (21).

7. Energy supply network for an electric vehicle, comprising: a low-voltage network (1) according to any one of claims 1 to 6; a high-voltage battery (21); a second DC-DC converter (22) designed to exchange electrical energy between the low-voltage network (1) and the high-voltage battery (21), wherein the high-voltage battery (21) and the second DC-DC converter (22) are arranged in a common housing element (2); and a high-voltage network (4), wherein the first DC-DC converter (11) of the low-voltage network (1) is connected to the high-voltage network (4), and wherein the high-voltage battery (21) is disconnectably electrically coupled to the high-voltage network (4).

8. Energy supply network according to claim 7, a photovoltaic system (3) which is connected to the photovoltaic connection (13) of the low-voltage network (1).

9. Method for operating a power supply network according to claim 7 or 8, comprising a first operating mode (S1), wherein electrical energy is transferred from the low-voltage network (1) to the high-voltage battery (21) using the first DC-DC converter (11) if a power flow from the R. 415155 - 21 - The photovoltaic system (3) operates in two modes: first, if the power flow from the photovoltaic system (3) to the low-voltage network (1) exceeds a predetermined first threshold; second, if the power flow from the photovoltaic system (3) to the low-voltage network (1) exceeds a predetermined first threshold and a predetermined second threshold; third, if the power flow from the photovoltaic system (3) to the low-voltage network (1) exceeds a predetermined first threshold and a predetermined second threshold; and third, if the power flow from the photovoltaic system (3) to the low-voltage network (1) falls below a predetermined second threshold, the first DC-DC converter (11) is deactivated and electrical energy is transferred from the high-voltage battery (21) to the low-voltage network (1) using the second DC-DC converter (22).

10. Method according to claim 9, wherein several electrical consumers (10a - 10c) are provided in the low-voltage network (1), and wherein the method deactivates at least one of the several electrical consumers (10a - 10c) when an electric vehicle is parked.

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