DE102014210283A1 - Method for operating a vehicle electrical system and vehicle electrical system - Google Patents

Abstract

The present invention discloses a method for operating a vehicle electrical system having at least two voltage levels, which have different rated voltages, and at least one voltage converter, which is arranged between the voltage levels, with the steps of detecting the electrical powers in the at least one voltage converter and / or the voltage levels, Calculating an optimum operating point for the at least one voltage converter based at least on the calculated electrical powers, driving the at least one voltage converter such that it is operated at the optimum operating point, wherein when operating the at least one voltage converter at the optimum operating point, the electrical losses in the Vehicle electrical system can be minimized.

Description

The present invention relates to methods for operating a vehicle electrical system with at least two voltage levels, which have different nominal voltages, and with at least one voltage converter, which is arranged between the voltage levels. Furthermore, the present invention relates to a corresponding vehicle electrical system.

State of the art

The electrical system z. B. an electric vehicle usually has a high-voltage network and a low-voltage network. The high-voltage network usually consists of a high-voltage battery and an electric motor. Other consumers with high power consumption can also be arranged in the high-voltage network, these can, for. B. air conditioning and heating consumers. The low-voltage network usually also has a battery and a variety of consumers such as lighting, control units, brake and steering actuators and comfort features.

A DC-DC converter between the two levels has the task of supplying the low-voltage side with energy. This is taken from the high-voltage battery, since its capacity is significantly greater than that of the low-voltage battery. The performance of the low-voltage on-board electrical system very much depends on the number of consumers installed at the low-voltage level and the loads used by the driver in the respective driving situation at the low-voltage level.

The power output of the DC-DC converter can therefore be only 5-10% of the rated power of the DC-DC converter in the smallest case. However, there are situations in which all of the nominal power or any power in between is retrieved. Depending on the converter technology and topology used, the efficiency of the voltage conversion depends on the magnitude of the converter output power P _WA in relation to the nominal power P _N , such as 8th shows.

Like in the 8th There is a wide range in which the DC-DC converter has optimum efficiency. This is in the range of 30% -80% of the rated power. On the other hand, the DC-DC converter in particular in the lower part-load operation, but also at rated power on worse efficiencies. In particular at partial load, z. B. below 10% of the rated power, this drops in the above example to less than 70%. The reason for this is, inter alia, that in each case the microcontroller of the DC-DC converter must be operated and the control of the switching elements of the DC-DC converter continues at 80-150 kHz. These power losses are significant, especially for small output power.

A known possibility for increasing the efficiency is to use multiphase converters, in which the number of active phases is a function of the load. Such transducers are very complex and require a complex control.

Today, the converter power is controlled so that either the low-voltage battery at a constant charge level, state of charge or SoC, adjusted or on the other hand, the electrical system voltage is set to a certain value, which in turn has an impact on the SoC of the low-voltage battery. These control strategies are not very flexible.

Disclosure of the invention

The present invention discloses a method with the features of patent claim 1 and a vehicle electrical system with the features of patent claim 7.

Accordingly, it is provided:

A method for operating a vehicle electrical system having at least two voltage levels, which have different nominal voltages, and at least one voltage converter, which is arranged between the voltage levels, with the steps of detecting the electrical powers in the at least one voltage converter and / or the voltage levels, calculating an optimum operating point for the at least one voltage converter based at least on the detected electrical powers, driving the at least one voltage converter such that it is in the optimum Operating point is operated, wherein in an operation of the at least one voltage converter in the optimum operating point, the electrical losses are minimized in the vehicle electrical system.

It is also provided:

A vehicle electrical system with at least two voltage levels, which have different nominal voltages, and at least one voltage converter, which is arranged between the voltage levels, and with a control device, which is designed to control the voltage converter based on a method according to the invention.

Advantages of the invention

The finding underlying the present invention is that the current approaches to increase the efficiency of the voltage converter over a wide power range, very complex and therefore are less goal-oriented.

The idea underlying the present invention is now to take this knowledge into account and to provide a possibility in which the regulation of the voltage converter does not take place based on a predetermined SoC of a battery or a nominal voltage of a voltage level of the electrical system.

Rather, the present invention provides that the electrical power is detected in the vehicle electrical system and an optimal operating point for the at least one voltage converter of the vehicle electrical system is calculated based on the detected electrical power.

In this case, an optimum operating point means that the electrical losses of the vehicle electrical system are minimized if the at least one voltage converter is operated at the calculated optimum operating point.

The regulation of the at least one voltage converter is based not only on the voltage of a low-voltage network or the state of charge of the low-voltage battery, but also on the losses incurred in the entire vehicle electrical system.

For example, consumers may, in an operating state with a low power consumption in a voltage level with a low nominal voltage of z. B. 12 volts, are fed from a 12 volt battery until it reaches a low SoC. Then, the corresponding voltage converter can be turned on and operated at an optimum operating point, so that the consumers are supplied with electrical energy and the 12 volt battery is recharged.

Thus, according to the present invention, a voltage converter can be operated in an on-board vehicle network in such a way that the total losses are minimized.

As a result, z. As DC / DC converters are much easier to design and developed and need not be developed with great effort to the widest possible power range with optimum efficiency.

Advantageous embodiments and further developments emerge from the dependent claims and from the description with reference to the figures.

In one embodiment, specifiable framework conditions are taken into account when calculating an optimal operating point. This allows a flexible adaptation of the operating strategy of a vehicle electrical system to different conditions.

In one embodiment, the predefinable boundary conditions have a minimum and / or a maximum state of charge of at least one energy store of at least one of the voltage levels. As a result, the life of the energy storage can be maximized.

In one embodiment, the predefinable boundary conditions have a minimum and / or a maximum voltage of at least one of the voltage levels. Will voltage fluctuations in the Voltage levels within specified limits allowed, the overall efficiency can be further improved.

In one embodiment, the specifiable boundary conditions have a minimum and / or a maximum number of charge and discharge cycles for at least one energy store of at least one of the voltage levels. As a result, the life of the energy storage can be further increased.

In one embodiment, the specifiable boundary conditions have a maximum charging and discharging current for at least one energy store of at least one of the voltage levels. This ensures that the energy storage devices are operated within their specifications and are not overloaded.

In one embodiment, the specifiable framework conditions have a predicted driving performance and / or a predicted driving time. This allows a specific adaptation of the operation of the vehicle electrical system for the predicted mileage or driving time. As a result, the efficiency is further improved.

In one embodiment, the predefinable boundary conditions have a predicated recuperation power in at least one of the voltage levels. Is predicted or predicted how high a recuperation, ie the energy z. B. from braking energy, the overall efficiency of the vehicle electrical system can also be improved.

In one embodiment, the specifiable framework conditions include an actual or predicted consumption of electrical power of at least one consumer in at least one of the voltage levels. If the consumption of electrical energy in the voltage levels is known or predicted, the control strategy can be adapted to this consumption and the efficiency can thus be further improved.

In one embodiment, when computing an optimal operating point, electrical energy quantities of energy stores of the voltage levels are further allocated specific energy costs and the specific energy costs for supplying the voltage levels with electrical energy are minimized. These specific energy costs may in one embodiment depend on the state of charge of the energy storage. For example, with full low-voltage battery whose energy costs to supply the low-voltage consumers are significantly lower than when the Niedervoltbrie is empty. This allows adaptation of the control strategy not only based on electrical powers in the voltage levels but also based on the source of electrical energy.

In one embodiment, the energy costs of the energy storage devices may also be dependent on the route to allow the battery to be discharged at the end of the travel route, but not discharged immediately at the beginning of the drive cycle. For this purpose, the duration of the drive cycle and its course must be predicted.

In one embodiment, the duration of the drive cycle and / or its course are predicted by accessing the data of a navigation system. Thereby, the driving cycle and / or its course can be determined very accurately.

In one embodiment, the energy costs of the energy storage depend on the internal resistance of the respective energy storage and thus z. B. from the temperature. As a result, the control of the at least one voltage converter can be further optimized.

In one embodiment, energy recovered by recuperation may be less expensive in energy storage than energy gained from charging. As a result, the control of the at least one voltage converter can be further optimized.

In one embodiment, energy transferred from a voltage converter to a voltage plane may be assigned cost values. In particular, the cost values for the voltage transformers can be dependent on the load on the voltage converter or the operating point of the respective voltage converter.

If the vehicle electrical system load is low, ie if a voltage converter is running at low efficiencies, it may therefore be better to feed the respective voltage level from the energy store of the voltage level itself.

If, on the other hand, the voltage transformer can be operated at high efficiency due to the on-board network load, the energy costs of the voltage converter are reduced.

In one embodiment, an energy store of a voltage level can be charged by deliberately operating the voltage converter at operating points with better efficiency. This control strategy is z. B. operating point shift called.

In one embodiment, environmental influences such as low temperatures, which make recuperation into two energy stores more effective than in one, since batteries here are subject to a limitation of the charging current, can be taken into account in the control of the at least one voltage converter.

In one embodiment, the optimal operating point for operation of the vehicle electrical system is calculated for a predetermined period of time. Further, the at least one voltage converter is controlled in the predetermined period based on the calculated optimum operating point. Thus, a forward-looking operating strategy for the vehicle electrical system can be provided, the z. B. includes an entire drive cycle.

In one embodiment, the vehicle electrical system has a high-voltage voltage level and a low-voltage voltage level and a voltage converter arranged between the high-voltage voltage level and the low-voltage voltage level. This arrangement makes it possible to provide a simple low complexity vehicle electrical system.

In one embodiment, the vehicle electrical system includes a high voltage voltage level, a midvoltage voltage level, and a low voltage voltage level. In this case, a first voltage converter is arranged between the high-voltage voltage level and the medium-voltage level, and a second voltage converter is arranged between the medium-voltage level and the low-voltage level. Alternatively, a first voltage converter is arranged between the high-voltage voltage level and the medium-voltage voltage level, and a second voltage converter is arranged between the high-voltage voltage level and the low-voltage voltage level. This arrangement makes it possible to easily adapt the vehicle electrical system to different requirements.

In one embodiment, the vehicle electrical system is used in an electric vehicle. As a result, the range of the electric vehicle can be optimized.

In one embodiment, the vehicle electrical system is also used in combustion engine powered vehicles with 48 V and / or 12 V electrical system voltages.

In one embodiment, the vehicle electrical system has more than two voltage levels. An exemplary embodiment has z. B. a high-voltage level, with z. B. 400 V rated voltage, a 48 V level and a 12 V level.

In one embodiment, the voltage levels may be formed as a sub-network of a vehicle.

The above embodiments and developments can, if appropriate, combine with each other as desired. Further possible refinements, developments and implementations of the invention also include combinations of features of the invention which have not been explicitly mentioned above or described below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

Brief description of the drawings

The present invention will be explained in more detail with reference to the exemplary embodiments indicated in the schematic figures of the drawings. It shows:

1 a flowchart of an embodiment of a method according to the invention;

2 a block diagram of an embodiment of a vehicle electrical system according to the invention;

3 a flowchart of another embodiment of a method according to the invention;

4 a block diagram of another embodiment of a vehicle electrical system according to the invention;

5 a block diagram of another embodiment of a vehicle electrical system according to the invention;

6 a block diagram of another embodiment of a vehicle electrical system according to the invention;

7 a diagram illustrating the losses in a vehicle electrical system; and

8th a diagram illustrating the efficiency of a voltage converter.

In all figures, the same or functionally identical elements and devices - unless otherwise stated - have been given the same reference numerals.

Embodiments of the invention

1 shows a flowchart of an embodiment of a method according to the invention for operating a vehicle electrical system 1 ,

The vehicle electrical system 1 has at least two voltage levels 2-1 - 2-3 on, which have different nominal voltages. Furthermore, the vehicle electrical system 1 at least one voltage transformer 3-1 - 3-2 on which between the voltage levels 2-1 - 2-3 is arranged.

The method sees in a first step S1 the detection of the electrical powers in the at least one voltage converter 3-1 - 3-2 or the voltage levels 2-1 - 2-3 in front. In one embodiment, the electrical power for the entire vehicle electrical system 1 , ie for the at least one voltage transformer 3-1 - 3-2 and the voltage levels 2-1 - 2-3 be recorded. In a further embodiment, but also only subnets of the vehicle electrical system 1 be considered, for. B. only one voltage level 2-1 - 2-3 ,

In a step S2, an optimal operating point for the at least one voltage converter 3-1 - 3-2 calculated at least based on the detected electrical power.

A third step S3, the method provides for driving the at least one voltage converter 3-1 - 3-2 before, wherein this is controlled such that it is operated at the optimum operating point.

In the context of this patent application, the operation of the at least one voltage converter means 3-1 - 3-2 in the optimal operating point that the electrical losses in the vehicle electrical system 1 be minimized.

To the electrical losses in the vehicle electrical system 1 To minimize these, they must be quantified.

This can be done in an embodiment in which the vehicle electrical system has two voltage levels, by means of the following equation, which z. B. from the 4 can be derived:

The index HV stands for a high-voltage level 2-1 in the vehicle electrical system 1 and the LV index for a low voltage voltage level 2-2 in the vehicle electrical system 1 , The high voltage voltage level 2-1 can z. B. have a rated voltage of 100 volts to 800 volts, in particular of about 400 volts. The low voltage voltage level 2-2 can z. B. have a rated voltage of 12 volts.

ist die Spannung einer Batterie in der Hochvolt-Spannungsebene 2-1,

ist der Innenwiderstand der Batterie in der Hochvolt-Spannungsebene 2-1.

ist die Spannung einer Batterie in der Niedervolt-Spannungsebene 2-2,

ist der Innenwiderstand der Batterie in der Niedervolt-Spannungsebene 2-2. P_HV ist die Leistung aller Verbraucher in der Hochvolt-Spannungsebene 2-1. P_LV ist die Leistung aller Verbraucher in der Niedervolt-Spannungsebene 2-2. Die Ausgangsleistung des Spannungswandlers 3-1 in die Niedervolt-Spannungsebene 2-2 wird mit

bezeichnet. Die Leistungsaufnahme des Spannungswandlers 3-1 aus der Hochvolt-Spannungsebene 2-1 wird mit

bezeichnet.In the above formula, P _{total loss represents} the total loss in the vehicle electrical system,

is the voltage of a battery in the high voltage voltage level 2-1 .

is the internal resistance of the battery in the high voltage voltage level 2-1 ,

is the voltage of a battery in the low voltage voltage level 2-2 .

is the internal resistance of the battery in the low voltage voltage level 2-2 , P _HV is the power of all consumers in the high voltage voltage level 2-1 , P _LV is the power of all consumers in the low-voltage level 2-2 , The output power of the voltage converter 3-1 in the low-voltage level 2-2 will with

designated. The power consumption of the voltage transformer 3-1 from the high voltage voltage level 2-1 will with

designated.

in

über die Approximation der Wirkungsgradkennlinie als Polynom enthalten sein.In one embodiment, the efficiency of the transducer as a function of

in

be included as a polynomial over the approximation of the efficiency curve.

With the equation shown above, the total losses for each operating point of the vehicle electrical system 1 calculated and optimized. This can be z. B. done with mathematical means of optimization.

Another possibility is the simulation of the total losses based on electrical and / or physical models in suitable simulation tools. The result of this modeling are maps in which the optimal converter power is calculated and stored for predefined operating points. Input variables of these maps are then the variables contained in the above formula, such as recordable SoC, drive power, power of the electrical system consumers, etc.

These maps can in the development or application of the converter or the converter control unit 5 based on the models created and then in the converter control unit 5 be stored. In the operation of the converter then do not have to perform the calculations above, but can be used on the offline created data.

A possible result of such a map calculation is for a fixed storage temperature, constant charge states of the electric storage and fixed high-voltage loads in 7 shown.

The knowledge of the loss-minimal converter power for a certain time is a necessary but not sufficient condition for an optimal operating strategy in the entire drive cycle. For example, the state of charge of the low-voltage battery 7-2 not considered. Discharging the low-voltage battery 7-2 Although in the short term minimal losses, but in the long run occur by charging the low-voltage battery 7-2 and the associated charging losses over the entire cycle seen significantly higher overall losses.

In order to avoid such problems, in one embodiment of the present invention, the optimum operating point for operation of the vehicle electrical system 1 calculated for a given period, the z. B. can correspond to a driving cycle. The optimal operating point is calculated in each case that over the entire predetermined period of the total losses in the vehicle electrical system 1 be minimized.

In a further embodiment, predefinable framework conditions are calculated when calculating an optimal operating point 4 considered.

These specifiable framework conditions 4 can z. B. a minimum and / or a maximum state of charge of at least one energy storage 7-1 - 7-3 at least one of the voltage levels 2-1 - 2-3 affect. The specifiable framework conditions 4 may also have a minimum and / or a maximum voltage of at least one of the voltage levels 2-1 - 2-3 affect. Furthermore, the specifiable framework conditions 4 a minimum and / or a maximum number of charge and discharge cycles for at least one energy store 7-1 - 7-3 at least one of the voltage levels 2-1 - 2-3 exhibit. Furthermore, the specifiable framework conditions 4 a maximum charging and discharging current for at least one energy store 7-1 - 7-3 at least one of the voltage levels 2-1 - 2-3 exhibit. The specifiable framework conditions 4 may also have a predicted driving performance and / or a predicted driving time. Additionally or alternatively, the specifiable framework conditions 4 a predicated recuperation power in at least one of the voltage levels 2-1 - 2-3 exhibit. Furthermore, the specifiable framework conditions 4 an actual or predicted consumption of electrical power of at least one consumer in at least one of the voltage levels 2-1 - 2-3 exhibit.

In addition, in calculating an optimum operating point, electric energy amounts of energy storage may further be added 7-1 - 7-3 the voltage levels 2-1 - 2-3 and / or from a voltage converter 3-1 - 3-2 energy transferred to a voltage level can be assigned specific energy costs and the specific energy costs for supplying the voltage levels 2-1 - 2-3 be minimized with electrical energy.

These specific energy costs depend on z. B. the state of charge of the electrical energy storage 7-1 - 7-3 from. For example, at full low voltage battery 7-2 their energy costs for the supply of low-voltage consumers significantly lower than when empty low-voltage battery 7-2 ,

Furthermore, the energy costs of the electrical energy storage 7-1 - 7-3 also be dependent on the route to allow the battery is discharged at the end of the route, but not immediately unloaded at the beginning of the driving cycle.

The energy costs of the electrical energy storage can also from the internal resistance of the energy storage 7-1 - 7-3 and thus z. B. depend on the temperature.

Energy recovered by recuperation can be stored in electrical energy stores 7-1 - 7-3 also have lower specific energy costs than energy gained from charging on a grid.

By the same principle is used by voltage transformers 3-1 - 3-2 into other voltage levels 2-2 - 2-3 , z. B. in the low-voltage level 2-2 , transferred electrical energy occupied with cost values.

Is the vehicle electrical system load low, ie the voltage converter is running 3-1 - 3-2 For low efficiencies, it may therefore be cheaper, the low-voltage level 7-2 from the energy store 7-2 the low-voltage level 7-2 to dine. Can, however, the voltage converter 3-1 - 3-2 due to the on-board network load are operated at high converter efficiencies, the energy costs of the voltage converter decrease 3-1 - 3-2 ,

A voltage converter in connection with this patent application, any voltage converter, in particular z. B. be a DC / DC converter.

2 shows a block diagram of an embodiment of a vehicle electrical system according to the invention 1 ,

The vehicle electrical system 1 has two voltage levels 2-1 and 2-2 on top of that by a voltage converter 3-1 be coupled with each other. Further, a control device 5 provided, which is adapted to the voltage converter 3-1 head for.

The two voltage levels 2-1 and 2-2 have different nominal voltages. In one embodiment, the voltage level 2-1 a high voltage voltage level 2-1 be and a rated voltage of 100 volts-800 volts, z. B. 400 volts. The voltage level 2-2 can z. B. a low voltage voltage level 2-2 and a rated voltage of less than 50 volts, z. B. of 12 volts or z. B. 48 volts.

The control device 5 is designed to carry out a method according to the invention and, based on the method, the voltage converter 3-1 so that it is operated at the calculated optimum operating point.

The vehicle electrical system according to the invention 1 can z. B. be used in an electric vehicle. Alternatively, the vehicle electrical system according to the invention 1 be used in any vehicle, which has more than one voltage level.

3 shows a flowchart of another embodiment of a method according to the invention.

The embodiment of the method according to 3 sees the measuring M of the electrical loads or services in the vehicle electrical system 1 , so in all voltage levels 2-1 - 2-3 of the vehicle electrical system 1 in front. To consider the framework conditions 4 Furthermore, the charge states and the temperatures of existing in the vehicle electrical system energy storage 7-1 - 7-3 , z. B. a high-voltage battery 7-1 and a low-voltage battery 7-2 detected.

Subsequently, in a pre-control step B, an optimal voltage converter power for the current time is calculated. This can be z. B. based on the above formula.

In a correction step K is then the optimum voltage converter performance for a given period, eg. B. a driving cycle calculated.

In the calculation of the optimal voltage converter performance for a given period go frame conditions 4 , such as B. a target curve for the SoC of an energy storage 7-1 - 7-3 , specific energy costs or the maximum allowed cyclization of energy storage 7-1 - 7-3 , one.

In the last step S, the voltage converter performance is finally taking into account further framework conditions 4 , such as B. allowed limits for a voltage converter power, charging and discharging and SoC limits for the energy storage 7-1 - 7-3 , discontinued.

4 shows a block diagram of another embodiment of an electrical system according to the invention 1 with a high voltage voltage level 2-1 and a low voltage voltage level 2-2 ,

In 4 are represented by arrows with unfilled bodies and streams by arrows with hatched bodies.

The high voltage voltage level 2-1 has a high-voltage battery 7-1 whose internal resistance in series with the circuit diagram of the high-voltage battery 7-1 as resistance R _{HVBatt is} shown. Parallel to the series connection of high-voltage battery 7-1 and resistor R _HVBatt is a load 8-1 which consumes a power P _HV and across which a voltage U _RHV drops. This load 8-1 is an equivalent circuit diagram of the consumers of the high voltage voltage level 2-1 intended.

The high-voltage battery 7-1 provides a voltage U _HVBatt and across the resistor R _HVBatt drops a voltage U _RHVBatt , resulting in a power P _RHV at the internal resistance of the high-voltage battery 7-1 is implemented.

From the battery the current I _{HVBatt which divides} into the current I _RHV , which flows over the load 8-1 flows, and the current I _WHV , which is in the voltage converter 3-1 flows. Between the voltage transformer 3-1 and ground is the voltage U _WHV on the high-voltage side. Furthermore, the voltage converter takes 3-1 the power P _WHV on the high-voltage side. On the low-voltage side there is the voltage converter 3-1 the power P _WLV off. The voltage is between the voltage transformer 3-1 and mass. The voltage converter 3-1 provides a current I _WLV on the low voltage side, which is in the low voltage level 2-2 flows. The low voltage voltage level 2-2 has a low-voltage battery 7-2 on, whose internal resistance as with the low-voltage battery 7-2 in series resistor R _{LVBatt is} shown, at which the power P _{RLV is} consumed. Parallel to the series connection of low-voltage battery 7-2 and _Resistor R _LVBatt is an equivalent circuit diagram for all consumers of the low voltage voltage level 2-2 a burden 8-2 drawn at which the voltage U _RLV drops and at which the power P _{LV is} implemented.

The low-voltage battery 7-2 provides the voltage U _LVBatt . The voltage U _RLVBAtt drops via the resistor R _LVBatt . From the low-voltage _battery U _LVBatt flows a current I _LVBatt which together with the current I _WLV from the voltage converter 3-1 in the load 8-2 flows.

The vehicle electrical system in 4 is formed with equivalent circuits representation of a vehicle electrical system according to the invention 1 , Based on this representation of the vehicle electrical system 1 can z. B. the above formula for loss calculation are derived.

5 shows a block diagram of another embodiment of a vehicle electrical system according to the invention 1 ,

The vehicle electrical system 1 of the 5 has three voltage levels 2-1 - 2-3 on, a high voltage voltage level 2-1 , a low voltage voltage level 2-2 and interposed therebetween a midvoltage voltage level 2-3 ,

A first voltage transformer 3-1 couples the midvolt voltage level 2-3 with the low-voltage level 2-2 , A second voltage converter 3-2 couples the high voltage voltage level 2-1 with the midvolt voltage level 2-3 ,

Each of the voltage levels 2-1 - 2-3 each has a voltage source 7-1 - 7-3 , z. B. a battery 7-1 - 7-3 , and a burden 8-1 - 8-3 on.

In 5 are the voltage levels 2-1 - 2-3 arranged in series, ie energy is from the high voltage voltage level 2-1 via the medium-voltage level 2-3 in the low-voltage level 2-2 transferred or vice versa. A direct transfer of energy between the high voltage voltage level 2-1 and the low voltage voltage level 2-2 is not scheduled.

6 shows a block diagram of another embodiment of a vehicle electrical system according to the invention 1 ,

The vehicle electrical system 1 of the 6 also has three voltage levels 2-1 - 2-3 on, a high voltage voltage level 2-1 , a low voltage voltage level 2-2 and a midvoltage voltage level 2-3 ,

In contrast to the vehicle Bornetz 1 of the 5 are the low voltage voltage level 2-2 and the midvoltage voltage level 2-3 but not in series with the high voltage voltage level 2-1 coupled. Rather, the low-voltage level 2-2 and the high voltage voltage level 2-1 coupled together, as in 4 shown. Parallel to the low voltage level 2-2 is the mid-voltage level 2-3 over the voltage converter 3-2 directly with the high voltage voltage level 2-1 coupled.

7 shows a diagram illustrating the losses in a vehicle electrical system 1 ,

The diagram shows the total losses in a vehicle electrical system 1 for different loads and different ratios between voltage converter power and load in the vehicle electrical system 1 shown at a power of the high-voltage vehicle electrical system of 10 kW, a temperature of 293 K and a SOC of the vehicle battery of 0.5.

The ordinate axis of the graph shows the total losses in watts. The abscissa axis of the diagram shows the ratio of converter power P _W to vehicle electrical system load P _BL . Finally, the Applikantenachse shows the on-board network load P _{LV of} the low-voltage vehicle electrical system.

It is in 7 clearly recognize that the losses are greatest when the load is very high and the ratio between the voltage converter power and load in the vehicle electrical system 1 is very big. It is in 7 It can also be clearly seen that the power loss at low power is almost constant. Ie. that the losses in relation to the performance at lower power more significant.

The present invention makes it possible to avoid such adverse operating conditions of the electrical system.

Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto, but modifiable in a variety of ways. In particular, the invention can be varied or modified in many ways without deviating from the gist of the invention.

Claims (9)

Method for operating a vehicle electrical system ( 1 ) with at least two voltage levels ( 2-1 - 2-3 ), which have different nominal voltages, and at least one voltage transformer ( 3-1 - 3-2 ), which between the voltage levels ( 2-1 - 2-3 ), comprising the steps of: detecting (S1) the electrical powers in the at least one voltage converter ( 3-1 - 3-2 ) and / or the voltage levels ( 2-1 - 2-3 ); Calculating (S2) an optimum operating point for the at least one voltage converter ( 3-1 - 3-2 ) based at least on the detected electrical power; Driving (S3) of the at least one voltage converter ( 3-1 - 3-2 ) such that it is operated at the optimum operating point; wherein during operation of the at least one voltage converter ( 3-1 - 3-2 ) at the optimum operating point the electrical losses in the vehicle electrical system ( 1 ) are minimized. A method according to claim 1, characterized in that when calculating an optimal operating point specifiable framework conditions ( 4 ). Method according to Claim 2, characterized in that the predefinable framework conditions ( 4 ) a minimum and / or maximum state of charge of at least one energy store ( 7-1 - 7-3 ) at least one of the voltage levels ( 2-1 - 2-3 ) exhibit; and / or that the specifiable framework conditions ( 4 ) a minimum and / or a maximum voltage of at least one of the voltage levels ( 2-1 - 2-3 ) exhibit; and / or that the specifiable framework conditions ( 4 ) a minimum and / or a maximum number of charge and discharge cycles and / or a maximum charge and discharge current for at least one energy store of at least one of the voltage levels ( 2-1 - 2-3 ) exhibit; and / or that the specifiable framework conditions ( 4 ) have a predicted driving performance and / or a predicted driving time; and / or that the specifiable framework conditions ( 4 ) a predicated recuperation power in at least one of the voltage levels ( 2-1 - 2-3 ) exhibit; and / or that the specifiable framework conditions ( 4 ) an actual or predicted consumption of electrical power of at least one consumer in at least one of the voltage levels ( 2-1 - 2-3 ) exhibit. Method according to one of the preceding claims, characterized in that when calculating an optimum operating point further electrical energy quantities of energy storage ( 7-1 - 7-3 ) of the voltage levels ( 2-1 - 2-3 ) and / or from a voltage converter ( 3-1 - 3-2 ) energy transferred to a voltage level can be assigned specific energy costs and the specific energy costs for supplying the voltage levels ( 2-1 - 2-3 ) are minimized with electrical energy. Method according to one of the preceding claims, characterized in that an optimum operating point for two voltage transformers ( 3-1 - 3-2 ), one of the voltage transformers ( 3-1 - 3-2 ) between a high voltage voltage level ( 2-1 ) and a midvoltage voltage level ( 2-3 ) and one of the voltage transformers ( 3-1 - 3-2 ) between the mid-voltage level ( 2-3 ) and a low-voltage level ( 2-2 ) is arranged. Method according to one of the preceding claims, characterized in that the optimum operating point for operation of the vehicle electrical system ( 1 ) is calculated for a given period of time; and the at least one voltage converter ( 3-1 - 3-2 ) is controlled in the predetermined period based on the calculated optimum operating point. Vehicle electrical system ( 1 ), with at least two voltage levels ( 2-1 - 2-3 ), which have different nominal voltages; and at least one voltage transformer ( 3-1 - 3-2 ), which between the voltage levels ( 2-1 - 2-3 ) is arranged; and a control device ( 5 ), which is adapted to the voltage converter ( 3-1 - 3-2 ) based on a method according to one of claims 1 to 6. Vehicle electrical system according to claim 7, characterized in that the vehicle electrical system ( 1 ) a high voltage voltage level ( 2-1 ) and a low voltage voltage level ( 2-2 ) and one between the high voltage voltage level ( 2-1 ) and the low-voltage level ( 2-2 ) arranged voltage transformer ( 3-1 - 3-2 ) having. Vehicle electrical system according to claim 8, characterized in that the vehicle electrical system ( 1 ) a high voltage voltage level ( 2-1 ), a midvoltage voltage level ( 2-3 ) and a low voltage voltage level ( 2-2 ) having; wherein a first voltage converter ( 3-1 - 3-2 ) between the high voltage voltage level ( 2-1 ) and the medium-voltage level ( 2-3 ) is arranged and a second voltage converter ( 3-1 - 3-2 ) between the mid-voltage level ( 2-3 ) and the low-voltage level ( 2-2 ) is arranged; or wherein a first voltage converter ( 3-1 - 3-2 ) between the high voltage voltage level ( 2-1 ) and the medium-voltage level ( 2-3 ) is arranged and a second voltage converter ( 3-1 - 3-2 ) between the high voltage voltage level ( 2-1 ) and the low-voltage level ( 2-2 ) is arranged.

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