DE102014201440A1 - Motor vehicle electrical system with optimized switching function - Google Patents

Abstract

Vehicle electrical system with a voltage converter (9), a traction battery (8) and a traction network (7), characterized in that the voltage converter (9) has a first operating state (30), in which the voltage converter (9) operates as buck converter and an electric Voltage (Ubatt) of the traction battery (8) to a voltage (U1) of the traction network (7) lowers, and a second operating state (31), in which the voltage converter (9) operates as a through switch and the electrical voltage (Ubatt) of the traction battery (8) without subscripts to the traction network (7) through.

Description

The invention relates to a vehicle electrical system with a voltage converter, a traction battery and a traction network, and a method that is used in a motor vehicle electrical system with such a voltage converter.

A traction battery for a motor vehicle, in particular for an electric vehicle, a hybrid vehicle, or a fuel cell vehicle includes a large number of battery cells, which are usually arranged in modules to meet the vehicle's performance and range requirements. Individual battery cells or battery modules are electrically connected in series, so that the electrical voltages of the battery cells or battery modules add up.

The range of electric vehicles can be increased by carrying more stored electrical energy in the vehicle. The energy content of a traction battery depends on its electrical capacity and electrical voltage. An increase in range can be done either by increasing the electrical capacity of the traction battery, or by increasing the voltage of the traction battery. A series connection of battery cells or battery modules, however, are limited by the limitations of power electronics. Currently, for example, in the vehicle high-voltage infrastructure for traction drives, the voltage limit is approximately 400-450 V. The electrical voltage can not be increased arbitrarily, since all components in the traction network have a maximum permissible upper voltage limit.

Typically, all components powered by the traction network are designed so that the maximum voltage on the traction battery is below the upper voltage limit of the components. Thus, the outputs of the traction battery can be connected directly to the traction network. However, this has the disadvantage that the voltage at the traction network in normal operation in the middle range of the state of charge is far below the maximum allowable operating voltage of the components on the traction network.

It is also known to increase the range of a motor vehicle by connecting several battery module strings in parallel within a traction battery and thus increasing the electrical capacity of the traction battery. Although this increases the range of the motor vehicle, but the disadvantage of the greatly changed voltage to the traction battery is maintained. Even with this solution, the voltage at the traction network in normal operation in the middle of the state of charge is far below the maximum allowable operating voltage of the components on the traction network.

From the European patent EP 1 889 349 For example, a vehicle power supply apparatus is known in which a voltage converter boosts the voltage of a secondary battery. A connection unit makes it possible to switch between a connection and a disconnection of the voltage set up by the voltage converter.

The German patent application DE 10 2012 200 577 A1 describes a method for controlling a battery. The battery includes several battery module strings. The battery module strings have a plurality of battery modules, wherein a battery module has a coupling unit. The coupling unit acts as a voltage converter and couples the battery modules together. The method allows a supply of a load with a predetermined and substantially constant overall performance. Battery modules of the battery module strings can each be connected in series. As a result, the output voltages of the battery modules of a series circuit can be summed to a higher phase voltage.

Object of the present invention is to improve a motor vehicle electrical system so that the above-mentioned disadvantages are at least partially overcome.

This object is achieved by the motor vehicle electrical system according to claim 1.

Further advantageous embodiments of the invention will become apparent from the subclaims and the following description of preferred embodiments of the present invention.

A motor vehicle electrical system according to the invention has a voltage converter, a traction battery and a traction network. The motor vehicle electrical system can be, for example, a motor vehicle electrical system for an electric vehicle, a hybrid vehicle, or a fuel cell vehicle.

The voltage converter has a first operating state in which it acts as a buck converter and lowers an electric voltage of the traction battery to a voltage of the traction network, and a second operating state in which it operates as a through-switch and the electric voltage of the traction battery without down setting to the traction network.

The voltage of a traction battery is not constant over its state of charge, but decreases with decreasing state of charge. Although the The voltage of a fully charged traction battery may be too high for the components on the traction network, this does not necessarily mean that it is also at a lower charge state. The voltage converter can thus be set up so that it reduces the voltage at the traction network only when the battery is fully charged and switches the voltage of the traction battery on the traction network from a certain state of charge.

For example, the voltage converter can be designed such that in the first operating state it lowers the voltage of the traction battery to a voltage upper limit of the traction network.

The operational state for the through-connection can be optimized for the function of the through-connection, so that losses during switching-through are reduced.

For plug-in hybrid vehicles, i. For hybrid vehicles, where it is possible to charge the traction battery externally, the hybrid operation usually starts when the traction battery is discharged to a low state of charge. In hybrid operation, the voltage converter in this exemplary use in a plug-in hybrid vehicle therefore does not have to work as a step-down converter in the first operating mode, but only needs to switch through. The voltage converter can therefore operate in this exemplary case in hybrid operation essentially in the second operating mode as a through switch.

According to one exemplary embodiment, the voltage converter has a switch which makes it possible to switch between the first operating state in which the voltage converter works as a buck converter and the second operating state in which the voltage converter works as a through-connection.

The switch, which allows switching between the first operating state and the second operating state of the voltage converter, can be designed, for example, as a relay, in particular as a contactor.

The switch, which allows switching between the first operating state and the second operating state of the voltage converter, but can also be designed as a semiconductor switch, for example as a MOSFET or IGBT.

The switch, which allows switching between the first operating state and the second operating state of the voltage converter, can be realized in a further embodiment functionally in transistors of the voltage converter, which also take over the function of voltage conversion.

Thus, the voltage converter described above can enable an optimized switching of the input voltage.

An exemplary automotive electrical system includes a traction battery, a traction network, and a voltage converter coupled between the traction battery and the traction network, as described above. For example, the voltage converter can be connected directly to the poles of a traction battery on the input side. On the output side, the voltage converter can directly feed a traction network with its consumers.

The traction battery may advantageously have at high values of the state of charge, an electrical voltage which is higher than the threshold voltage of the traction network. Thus, in the vehicle electrical system, a traction battery can be used, which has a voltage in the fully charged state, which is above the voltage upper limit of the traction network. This makes it possible to design the maximum voltage on the traction battery so that it lies above the maximum operating voltage of the components on the traction network.

The traction network may include power electronics (e.g., an inverter) that converts electrical energy from the traction network to operate an electric machine.

Furthermore, a low-voltage on-board electrical system can be coupled to the traction network via a further voltage converter which is coupled between the traction network and the low-voltage electrical system, reduces the electrical voltage of the traction network to the voltage level of the low-voltage network and supplies electrical energy from the traction network to the low-voltage vehicle electrical system. The low-voltage on-board electrical system can be, for example, a conventional 12V vehicle electrical system.

The traction network may further include other consumers coupled to the traction network, such as an air conditioning compressor or a heater.

In the case of an electric vehicle or a plug-in hybrid, the traction battery can also be charged by means of an external charger with electrical energy. In this case, the voltage converter according to the invention can serve to raise the voltage of the charger to the voltage of the traction battery.

A method of operating a vehicle electrical system having a traction battery, a traction network, and a voltage converter coupled between the traction battery and the traction network comprises: detecting the traction battery electrical voltage, driving the voltage converter to a first Operating state is offset, in which the voltage converter operates as a buck converter and deepens a voltage of the traction battery to a voltage limit of the traction network, if the voltage of the traction battery is above the voltage limit of the traction network, and driving the voltage converter such that this in a second operating state is offset, in which the voltage converter operates as a through switch and the electrical voltage of the traction battery without subscrit to the traction network turns on, if the voltage of the traction battery is smaller o which is equal to the voltage limit of the traction network. The method can be executed by a controller. The voltage converter may receive corresponding control signals from, for example, a battery management system, or other control center such as a motor controller.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

1 schematically shows an embodiment of a motor vehicle with an electrical system;

2 schematically shows a voltage converter according to an embodiment of the invention;

3 schematically shows the voltage curve of a traction battery as a function of their state of charge; and

4 schematically shows an exemplary driving operation selection of a plug-in hybrid vehicle depending on the state of charge of a traction battery.

An exemplary embodiment of a motor vehicle in which the voltage converter according to the invention can be used is shown schematically in FIG 1 shown. The car 1 is constructed here by way of example according to the principle of parallel hybrid. When parallel hybrid are both an internal combustion engine 2 as well as an electric machine 3 via a gearbox 4 mechanically to a drive axle 5 coupled. The from the combustion engine 2 discharged mechanical energy is by means of the electric machine 3 converted into electrical energy and with the help of power electronics, in particular an inverter 6 via a first voltage converter according to the invention 9 in a traction battery 8th fed. The traction battery 8th can electrical energy through the traction network 7 to the electric machine 3 provide. Conversely, the internal combustion engine 2 delivered mechanical energy (or recuperative from the drive axle 4 recovered mechanical energy) of the traction battery 8th be supplied. With the traction network 7 is via a second voltage converter 10 furthermore also a low-voltage on-board network 11 coupled, which is exemplified here as a 12V electrical system. With the traction network 7 are also other high-voltage consumers 12 coupled, here for example an air conditioning compressor. The traction network 7 , the power electronics 6 and the high-performance consumers 12 be from the traction battery 8th fed and are at a voltage level through the first voltage converter 9 is given. The first voltage transformer 9 this exemplary motor vehicle 1 that is between the traction battery 8th and the traction network 7 is preferably realized by the voltage converter according to the invention.

The exemplary motor vehicle 1 can be operated in different operating states. In a first operating state, the motor vehicle 1 burned by means of power from the internal combustion engine. Part of the energy generated by the internal combustion engine is used to regenerate electrical energy. Low-voltage consumers of the low-voltage network are using this generically generated electrical energy 11 and high-voltage consumers 12 provided. In a second operating state, the motor vehicle 1 burned by means of power from the internal combustion engine and generator-generated electrical energy is the traction battery 8th supplied to load these. In a third operating state, the motor vehicle 1 purely electric with energy from the traction battery 8th hazards. In a fourth operating state, the motor vehicle 1 by means of power from the internal combustion engine "burned" driven and electrical energy from the traction battery 8th is used to support the combustion (boosting). In a fifth operating state, electrical energy is recuperatively recovered and the traction battery 8th fed.

2 schematically shows an exemplary embodiment for the first voltage converter 9 of the motor vehicle 1 that between traction battery ( 8th in 1 ) and traction network ( 7 in 1 ) and is an embodiment of the present invention. The voltage converter 9 takes over connections 21 a source voltage Ubatt contrary. The connections 21 are For example, with the two poles of a traction battery ( 8th in 1 ) coupled. The voltage converter 9 has a first switching transistor T1 and an anti-parallel connected first diode D1, which together form a first switching element 22 form. The voltage converter 9 further comprises a second switching transistor T2 and an anti-parallel connected second diode D2, which together form a second switching element 23 form. The two switching elements 22 . 23 are using control signals 24 from a drive 20 driven. For example, the two transistors T1 and T2 may each be implemented as a field effect transistor (FET), in particular as a MOSFET, or as an insulated gate bipolar transistor (IGBT). As an alternative to the transistors T1, T2 and turn-off thyristors could be used. The transistors T1, T2 are controlled by the driver 20 with a control signal 24 driven in a manner known to those skilled in the art, whereby they change at very short intervals between the conductive and insulating state. The control signals 24 For example, a control method for voltage transformers known to the person skilled in the art can be implemented by means of pulse width modulation (PWM) or pulse frequency modulation (PFM). Depending on the switching state of the switching units 22 and 23 is a coil L1 either electrical energy from the source voltage Ubatt (eg from the traction battery 8th in 1 ), or electrical energy taken from the coil L1 and a load (eg the traction network 7 out 1 ) at an exit 25 of the voltage converter 9 provided with an output voltage U1. The voltage converter 9 can work as a buck converter.

In a first switching state, transistor T1 is closed and transistor T2 is open. In this first switching state, current flows from the traction battery ( 8th in 1 ) via the coil L1 in the traction network ( 7 in 1 ). In a second switching state, both transistors T1 and T2 are open. In this second switching state, current flows via the coil L1 and diode D2 into the traction network ( 7 in 1 ), whereby high losses occur at diode D2. In a third switching state, transistor T1 is open and transistor T2 is closed. In this third switching state, current flows through the coil L1 and transistor T2 without losses in the traction network ( 7 in 1 ). In a fourth switching state, both transistors T1 and T2 are both open. This fourth switching state corresponds to the second switching state.

By means of the control signals 24 a duty cycle can be controlled, which determines the proportionality factor with a step-down converter, with which the source voltage Ubatt is converted into the output voltage U1.

For additional smoothing of the output voltage U1 in the embodiment, a smoothing capacitor C1 to the output 25 of the voltage converter 9 connected in parallel.

The voltage converter 9 This embodiment has a switch S1, which makes it possible to switch between a first operating state and a second operating state. In the first operating state (open switch S1), the voltage converter operates 9 as a buck converter and sets the source voltage Ubatt to an output voltage U1 deep. In the second operating state (closed switch S1), the voltage converter operates 9 as a through-switch and switches the source voltage Ubatt without lowering to the output 25 by, so that the output voltage U1 is equal to the source voltage Ubatt. The switch S1 is formed in this embodiment as a contactor, which can be switched by means of an electrical control signal. Alternatively, the switch S1 could also be realized as a field-effect transistor, in particular as a MOSFET. A MOSFET has the advantage that the switch S1 has a high efficiency.

In yet an alternative embodiment, the switch S1 may also be functionally connected through the transistors (T1, T2 in FIG 1 ) of a voltage converter are realized, which take over the function Tiefsetzung the source voltage. In this embodiment, transistor T1 is permanently closed and transistor T2 is opened. In this case, the step-down ratio, with which the source voltage Ubatt is converted into the output voltage U1, results from the losses at the coil L1.

The switch S1 is controlled by means of electrical signals of a control unit (not shown). This control unit can also, for example, the specifications for the voltage conversion for the control 20 specify, for example, the proportionality factor of the voltage conversion. The voltage converter may receive corresponding control signals from, for example, a battery management system, or other control center such as a motor controller. The corresponding control signals may be provided to the voltage converter via an electronic communication path, such as a vehicle bus system, in a manner known to those skilled in the art. The control center can perform the control of the voltage converter in dependence on other state variables, in particular depending on the state of charge of the traction battery, which is known to the battery management system.

The voltage converter 9 This embodiment can be operated bidirectionally. The voltage converter sets in one direction 9 a high voltage of the traction battery 8th to a lower voltage of the traction network 7 down and feeds electrical energy from the traction battery 8th into the traction network 7 one. In a reverse direction sets voltage converter 9 a low voltage of the traction network 7 to a higher voltage of the traction battery 8th high and carries electrical energy from the traction network of the traction battery 8th to.

3 schematically shows the voltage curve of a traction battery as a function of their state of charge. The state of charge (also called "state of charge", in short SoC) is a characteristic value for the state of charge of batteries. The state of charge value indicates the still available charge amount of a battery in relation to the nominal value, ie of the available charge amount in the fully charged state. The state of charge value is given as a percentage of the nominal value. A charge state value of 50% means, for example, that the battery still has a remaining charge of 50% based on the full charge of 100%. A battery module with a nominal capacity of 28 Ah, for example, has a charge state value of 50% only a removable amount of charge of 14 Ah. The state of charge value of a battery module can be determined in the manner known to the person skilled in the art, for example by voltage measurement, on a current-integrative basis, by measuring the impedance, in batteries with liquid electrolyte on a chemical basis, or in NiMH batteries by means of the dependency of the charge state value on the internal pressure. The method of voltage measurement uses predetermined discharge curves to determine the state of charge value. In the current-integrative method, the charge state value is determined via the battery current during an integration time. Furthermore, a combination of two or more of said methods is possible.

At maximum state of charge SoC (equal to or near 100%), the voltage of the traction battery is exemplary at a final charging voltage of Ubattmax = 550 V. This final charging voltage Ubattmax is greater than the voltage upper limit Umax of a traction network, which is assumed here as Umax = 400 V, for example. The voltage converter operates in this range of high state of charge values in an operating mode in which it lowers the voltage Ubatt to the maximum permissible limit voltage Umax. With decreasing state of charge SoC the voltage Ubatt of the traction battery decreases. At a state of charge of about 70%, the voltage Ubatt of the traction battery reaches the voltage upper limit Umax of the traction network of 400 V. From here, a lowering of the voltage Ubatt of the traction battery is no longer required. The voltage converter is switched to its second mode of operation by switching the traction voltage Ubatt to the traction network without stepping down. With increasing emptying of the traction battery, the voltage Ubatt of the traction battery drops further until it reaches a discharging final voltage of Ubattmin from here exemplary 300 V with complete emptying of the traction battery. An inventive voltage converter thus operates in two operating states. At a voltage of the traction battery, which is greater than the voltage upper limit of the traction network, the voltage converter operates in a first operating state in which it lowers the voltage of the traction battery to the voltage upper limit of the traction network. This operating state is in the diagram of 3 by double arrow 30 characterized. At a voltage of the traction battery, which is smaller than the (or equal to) the voltage upper limit of the traction network, the voltage converter operates in a second operating state, in which he turns on the voltage Ubatt of the traction battery without downsizing the traction network. This operating state is in the diagram of 3 by double arrow 31 characterized. In 3 Furthermore, a nominal voltage Ubattnom of the traction battery is also shown, which here is Ubattnom = 384 V by way of example.

4 schematically shows an exemplary driving operation selection of a plug-in hybrid vehicle depending on the state of charge SoC of a traction battery. The traction battery is charged by external charging up to a maximum state of charge of 95%. Up to a state of charge of 25% is a purely electric driving. This purely electric driving is in 4 through the double arrow 32 characterized. Between a state of charge of 25% and a minimum state of charge of 10% is a hybrid driving operation. This hybrid ride is in 4 by a double arrow 33 characterized. A comparison of the driving conditions of the 4 with the switching ranges of the voltage converter off 3 shows that a voltage converter according to the invention in hybrid operation in its second operating state ( 31 ) can be held in which he works as a through switch and transfers the voltage of the traction battery without downsizing to the traction network.

LIST OF REFERENCE NUMBERS

1

motor vehicle

2

internal combustion engine

3

electric machine

4

transmission

5

drive axle

6

Inverter (power electronics)

7

traction power

8th

traction battery

9

first voltage converter

10

second voltage converter

11

Low-voltage onboard network

12

High-voltage consumer (eg air conditioning compressor)

20

control

21

Connections for source voltage Ubatt

22

switching unit

23

switching unit

24

control signals

25

Connections for output voltage U1

T1

transistor

T2

transistor

D1

diode

D2

diode

C1

capacitor

L1

Kitchen sink

S1

Switch (e.g. contactor)

U1

Source voltage (e.g., of traction battery)

U2

Output voltage (e.g., for traction network)

30

first operating state (buck converter)

31

second operating state (through switch)

32

electrical operation

33

hybrid operation

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1889349 [0006]
• DE 102012200577 A1 [0007]

Claims (10)

Motor vehicle electrical system with a voltage converter ( 9 ), a traction battery ( 8th ) and a traction network ( 7 ), characterized in that: the voltage transformer ( 9 ) a first operating state ( 30 ), in which the voltage transformer ( 9 ) works as a buck converter and an electrical voltage (Ubatt) of the traction battery ( 8th ) to a voltage (U1) of the traction network ( 7 ) and a second operating state ( 31 ), in which the voltage transformer ( 9 ) operates as a through switch and the electrical voltage (Ubatt) of the traction battery ( 8th ) without subsidence to the traction network ( 7 ) switches through. Motor vehicle electrical system according to claim 1, wherein the voltage converter ( 9 ) is designed so that in the first operating state ( 30 ) the tension of the traction battery ( 8th ) to a voltage upper limit (Umax) of the traction network deepens. Motor vehicle electrical system according to one of the preceding claims, wherein the voltage converter ( 9 ) further comprises a switch (S1) that switches between the first operating state ( 30 ), in which the voltage transformer ( 9 ) operates as a buck converter, and the second operating state ( 31 ), in which the voltage transformer ( 9 ) works as a through switch allows. Motor vehicle electrical system according to claim 3, wherein the switch (S1) of the voltage converter ( 9 ) is designed as a contactor, or as a field effect transistor, in particular as a semiconductor switch, in particular as a MOSFET or IGBT. Motor vehicle electrical system according to Claim 3, in which the switch (S1) is functionally connected to transistors (T1, T2) of the voltage converter ( 9 ) is realized, which also take over the function of the voltage conversion. Motor vehicle electrical system according to one of the preceding claims, wherein the voltage converter ( 9 ) between the traction battery ( 8th ) and the traction network ( 7 ) is coupled. Motor vehicle electrical system according to Claim 6, in which the traction battery ( 8th ) at high values of the state of charge (SoC) has an electrical voltage (Ubatt) which is higher than the limit voltage (Umax) of the traction network ( 7 ). Motor vehicle electrical system according to Claim 6 or 7, in which the traction network ( 7 ) a power electronics ( 6 ), the electrical energy from the traction network ( 7 ) for the operation of an electric machine ( 3 ). Motor vehicle electrical system according to one of claims 6-8, further comprising a low-voltage vehicle electrical system ( 11 ) and another voltage converter ( 10 ), the low-voltage on-board electrical system ( 12 ) to the traction network ( 7 ), the electrical voltage (U1) of the traction network ( 7 ) reduces to the voltage level of the low-voltage network and electrical energy from the traction network ( 7 ) the low-voltage on-board electrical system ( 11 ) feeds. Method for operating a vehicle electrical system with a traction battery ( 8th ), a traction network ( 7 ) and a voltage converter ( 9 ) according to any one of claims 1-5 connected between the traction battery ( 8th ) and the traction network ( 7 ), comprising determining the electrical voltage of the traction battery ( 8th ), Driving the voltage converter ( 9 ) such that this in a first operating state ( 30 ), in which the voltage transformer ( 9 ) works as a buck converter and an electrical voltage (Ubatt) of the traction battery ( 8th ) to a voltage limit (Umax) of the traction network ( 7 ), if the voltage (Ubatt) of the traction battery exceeds the voltage limit (Umax) of the traction network ( 7 ), and driving the voltage converter ( 9 ) such that this in a second operating state ( 31 ), in which the voltage transformer ( 9 ) operates as a through switch and the electrical voltage (Ubatt) of the traction battery ( 8th ) without subsidence to the traction network ( 7 ), if the voltage (Ubatt) of the traction battery is less than or equal to the voltage limit (Umax) of the traction network ( 7 ).

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