DE102018213130A1 - Electrical vehicle electrical system and motor vehicle with such an electrical system - Google Patents

Abstract

The invention relates to an electrical system (4) for a motor vehicle (2) with an inverter (16) with at least one bridge branch (18), which bridge branch (18) has two series-connected switches (22) and a center tap (24) between the switches (22), and with two load connections (10), the bridge arm (18) of the inverter (16) being connected in series between the load connections (10), and wherein in a current path (26) between the center tap (24) and one the load connections (10), an inductor (28) and a DC voltage source (20) for setting a voltage (U) at the load connections (10) are connected in series to a predetermined voltage value. The invention further relates to a method for operating such an electrical system (4) and an electrically driven motor vehicle (2) with such an electrical system (4).

Description

The invention relates to an electrical system for a motor vehicle, with an inverter. Furthermore, the invention relates to a method for operating an electrical vehicle electrical system and an electrically driven motor vehicle with such an electrical system.

A motor vehicle typically has a DC voltage network with an electrical consumer (vehicle application), such as a headlight or an air conditioning system, the DC voltage network for its operation being connected to load connections (terminals) of a DC voltage source, in particular in the form of a battery. Furthermore, for example, a control unit, also referred to as an operational management system, is provided, by means of which the DC voltage source is connected to the load connections and thus to the DC voltage network when predetermined conditions are met, so that the DC voltage source provides an electrical voltage at its load connections (terminals) for the DC voltage network ,

A prerequisite for switching on the DC voltage source is, for example, that an electrical voltage is already present at the load connections, which essentially corresponds to the voltage provided by the DC voltage source. In other words, a predetermined voltage value must be set on the load connections. In this way, when the battery is connected to the load connections, a comparatively large (connection) current through the DC voltage network and possible damage to components of the DC voltage network associated therewith are avoided or the risk of damaging them is at least reduced. In other words, a prerequisite is that the DC voltage network is precharged.

For example, a so-called precharge resistor is used for precharging the DC voltage network. The precharge resistor is connected between the DC voltage source and the load connections, the precharge resistor causing a limitation and a reduction in the (connection) current.

So is from the EP 2 786 891 A1 a battery system with a plurality of cells and with a load circuit is known to which the voltage of the cells is applied. Furthermore, the battery system comprises a current sensor which is set up to detect the current flowing in the load circuit, and a precharge circuit which can be connected to the load circuit and which is set up to limit the current flowing through the load circuit by means of a resistor. Furthermore, the battery system has a disconnecting device connected in parallel with the precharge circuit, by means of which the precharge circuit can be bridged.

Such a precharge resistor is an additional component which increases manufacturing costs and for which additional installation space is required. In particular, an ohmic loss due to the precharge resistor is also comparatively large. Furthermore, the precharge resistance of the precharge can heat up in the course of the current limitation.

As an alternative to this, the (first) DC voltage network is precharged, for example by means of a second DC voltage source or by means of a second DC voltage network, in particular with a comparatively low voltage. Here, the second DC voltage source or the second DC voltage network is connected to the first DC voltage network via a DC voltage converter, so that a voltage provided by the second DC voltage source or by the second DC voltage network is adapted by means of the DC voltage converter to the voltage value specified by the control device, i.e. the output voltage of the DC voltage converter is set accordingly.

If the DC voltage network does not already have such a DC voltage converter, this is an additional component, which is why manufacturing costs are increased and additional installation space is necessary.

The invention has for its object to provide a suitable electrical system for precharging a DC voltage network. Furthermore, a method for operating the electrical vehicle electrical system and an electrically driven motor vehicle with such an electrical system are to be specified.

With regard to the electrical vehicle electrical system, the object is achieved according to the invention by the features of claim 1. With regard to the method, the object is achieved according to the invention by the features of claim 7 and with respect to the motor vehicle by the features of claim 10. Advantageous refinements and developments are the subject of the dependent claims. The explanations in connection with the electrical vehicle electrical system also apply analogously to the method and to the motor vehicle and vice versa.

The electrical vehicle electrical system is provided and set up for a motor vehicle, in particular an electrically driven motor vehicle. The vehicle electrical system, which is also referred to as the supply network, points here an inverter with at least one bridge branch (half bridge), which in turn comprises two series switches and a center tap between the switches. Furthermore, the vehicle electrical system has two load connections, the bridge arm of the inverter being connected in series between these load connections. In summary, the load connections, the two switches and the center tap are connected in series accordingly.

Furthermore, an inductance and a DC voltage source for setting an electrical voltage at the load connections to a predetermined voltage value are connected in series in a current path between the center tap and one of the load connections. In particular, the phase connection (positive pole, (+) pole) of the DC voltage source is connected to the inverter.

The DC voltage source, the inductance and the switches of the inverter form an (inductive) DC voltage converter. If the two switches are switched accordingly, a current flows through the inductance, as a result of which a magnetic field is generated. An energy corresponding to the magnetic field is therefore temporarily stored by means of the inductance.

For this purpose, the (first) switch which is connected between the center tap and the load connection connected to the current path is in particular switched to be current-conducting. In other words, the first switch connected in parallel with the current path is closed for this purpose. When this switch is opened, that is, when the switch is switched off, a voltage or a current is induced by means of the inductance. When the other (second) switch is electrically conductive, a corresponding voltage is then applied to the load connections. By means of a suitable switching of the first switch, in particular by means of a pulse width modulation with a suitable duty cycle (pulse-pause ratio, duty cycle), a temporal mean value of the voltage at the load connections can be set and expediently also set. In this way, it is possible for the (output) voltage at the load connections to be adapted to a predetermined voltage value. In an expedient embodiment, the electrical vehicle electrical system has a control unit for controlling the switches. In this case, it is preferably connected to control inputs of the switches.

In an advantageous embodiment, a capacitor is connected as a so-called charging capacitor between the load connections and parallel to the bridge arm of the inverter. The capacitor is charged based on the induced voltage and the voltage of the DC voltage source, so that a greater voltage is present at the capacitor than the DC voltage source provides. A step-up converter (step-up converter, boost converter, step-up converter) is thus formed. In other words, the DC-DC converter is designed as a step-up converter. In this way it is possible to set the voltage at the load outputs, that is to say the output voltage, to a value which is greater than that of the DC voltage source. In summary, the capacitor is charged in the course of precharging and then serves in particular to maintain the voltage present at the load connections, for example also during the charging process of the inductor, in other words when the inductor flows with appropriate switching of the two switches.

In summary, the voltage at the load outputs can be adjusted by means of the direct voltage converter or the step-up converter formed in this way. In particular, the voltage is adjusted in accordance with a predetermined voltage value. As a result, a DC network connected to the load connections can be precharged. For example, the DC voltage source is a 12V battery for a circuit for driving the electrically driven motor vehicle, which circuit is also referred to below as the drive train. The voltage of this DC voltage source is in particular converted (boosted) by means of the DC voltage converter designed as a step-up converter, so that a (application) DC voltage network of the motor vehicle, for example designed for 24V or 48V, is provided and set up, for example, for vehicle applications such as air conditioning or a headlight , can be preloaded and advantageously also preloaded.

The inverter and the DC voltage source are particularly preferably already part of a circuit present in the motor vehicle, in particular the drive train. The inverter and the DC voltage source are therefore no additional components to be introduced into the motor vehicle. Rather, existing means, that is to say the inverter and the DC voltage source, are used to set a voltage at the load connections and advantageously precharge the (application) DC voltage network.

In an advantageous development, according to a first variant, the inductance is that of an electrical machine, in particular a three-phase motor for driving the motor vehicle. With others A phase winding of the electrical machine is used as the inductance. As a result, the inductance is also advantageously already a component of the drive train and thus not a component which has to be introduced separately into the motor vehicle. However, it must be noted that a torque is generated when the current flows through a phase winding of the electrical machine designed as a three-phase motor. To avoid such a torque, in an alternative configuration, which is referred to here as the second variant, the inductance is a coil which is separate from the electrical machine and which is integrated in the drive train as a further component. For example, the coil is part of a vehicle component or is connected to the vehicle electrical system as an additional component.

In particular, the capacitor also serves to smooth a current and / or a voltage when the inverter is operating in order to generate the three-phase current for the electrical machine. The capacitor is thus already provided in the vehicle electrical system and does not form a separate component that is only to be introduced for the purpose of precharging.

According to a suitable embodiment of the first variant, the inverter has three bridge branches, each of which comprises two switches connected in series and a center tap between the switches. A phase winding of the electrical machine is connected to the center taps. The inverter therefore serves to generate the three phases (currents) for the operation of the electrical machine, which is designed in particular as a three-phase motor. The DC voltage source is connected to one of the center taps, ie directly connected to one of the phase windings.

The phase connections are interconnected, for example by means of a delta connection or a star connection. As a result, two of the center taps are also connected to one another via the corresponding phase windings. The inductance of the DC-DC converter or the step-up converter is consequently formed by means of the inductances of these two phase windings.

In an advantageous embodiment, the switches of the or each bridge branch are designed as semiconductor switches. These are particularly preferably self-locking n-channel MOSFETs (metal oxide semiconductor field effect transistors). As an alternative to this, the switches are, for example, bipolar transistors with an insulated gate electrode (IGBT), in each case one diode being connected in parallel to the associated bipolar transistor, the forward direction of which is antiparallel (opposite) to the forward direction of the bipolar transistor. As a result, the capacitor of the step-up converter is prevented from being discharged via the current path having the inductance. In the case of the execution as a MOSFET, however, this already prevents the so-called body diode of the MOSFET, so no additional diode is necessary.

The phase connection of the DC voltage source is suitably guided to the center tap. The (first) switch of the bridge branch forming the DC voltage converter or step-up converter, which switch is connected between the center tap and the load connection connected to the ground connection of the DC voltage source, is connected to the center tap on the drain side. The other (second) switch of this bridge branch is connected on the source side to the center tap and on the drain side to the other load connection.

A further switch is preferably additionally connected in the current path, in particular between the direct current source and the inductor. Using this, the DC voltage source can be switched on or off (precharged, disconnectable) depending on the switch position for precharging. If the switch is switched off, in particular after the DC voltage network has been precharged, influencing the (normal) operation of the inverter, for example for generating the rotating field of the electrical machine, is advantageously avoided.

According to an advantageous development, a voltage at the load connections of the electrical vehicle electrical system is set to a predetermined voltage value in a method for operating an electrical system which is embodied in one of the variants shown above. In this way, a voltage for precharging a DC voltage network is advantageously provided by means of the on-board electrical system.

According to a suitable embodiment, the voltage provided by the DC voltage source of the electrical system is converted. If the specified voltage value is greater than the voltage provided by the DC voltage source, it is converted upwards.

Furthermore, in an advantageous further development, the switches of the inverter are controlled in accordance with a suitable embodiment in such a way that the switches, the capacitor and the inductors act as direct voltage converters, in particular as step-up converters, for the direct voltage source. In other words, the switch of the inverter, the capacitor and by means of the inductors, with suitable activation of the switches of the inverter, a direct voltage converter, in particular an up converter, is formed. In addition, the inductance of a phase winding of an electrical machine is preferably used as the inductance.

In a further advantageous embodiment, an electrically driven motor vehicle has an electrical system in one of the variants described above. In particular, components already present in its drive train, namely at least the inverter and the DC voltage source, are used to provide a voltage set to a predetermined voltage value. This can and is expediently used for precharging a DC voltage network.

• 1 schematisch ein elektrisch angetriebenes Kraftfahrzeug mit einem elektrischen Bordnetz, wobei dessen Anwendungsbatterie über eine Steuervorrichtung einem Gleichspannungsnetz zuschaltbar ist, und wobei das Gleichspannungsnetz an eine Schaltung zum Antrieb des Kraftfahrzeugs angeschlossen ist,
• 2 in einem schematisierten Schaltbild das Bordnetz, welches eine Gleichspannungsquelle sowie einen Wechselrichter mit Brückenzweigen aufweist, wobei die Gleichspannungsquelle über eine als Spule ausgebildete Induktivität an einen Mittenabgriff zwischen zwei Schaltern einer der Brückenzweige angeschlossen ist,
• 3 in einem schematisierten Schaltbild eine alternative Ausgestaltung des Bordnetzes der 1, wobei die Induktivität diejenige einer elektrischen Maschine ist, und
• 4 in einem Flussdiagramm einen Verfahrensablauf zum Betrieb des Bordnetzes.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. In it show:

• 1 schematically an electrically driven motor vehicle with an electrical vehicle electrical system, the application battery of which can be connected to a DC voltage network via a control device, and the DC voltage network being connected to a circuit for driving the motor vehicle,
• 2 In a schematic circuit diagram, the vehicle electrical system, which has a DC voltage source and an inverter with bridge branches, the DC voltage source being connected via an inductance designed as a coil to a center tap between two switches of one of the bridge branches,
• 3 in a schematic circuit diagram an alternative embodiment of the electrical system of the 1 , the inductance being that of an electrical machine, and
• 4 in a flowchart a procedure for operating the vehicle electrical system.

Corresponding parts and sizes are always provided with the same reference symbols in all figures.

In 1 is schematically an electrically powered motor vehicle 2 shown. This has an electrical system 4 , which in turn comprises two subnets. The first subnet 4a is a DC network with an electrical or electronic consumer 6 , which is representative of an ohmic resistance here. Here is the first subnet 4a for its operation with a (application) battery 8th connected load connections 10 connected. Furthermore, there is a control unit called an operational management system 12 to a switch 14 the battery 8th connected by means of which the battery 8th to the load connections 10 is connectable. the battery 10 provides a voltage of 24 V or 48 V for the consumer, for example 6 ready.

It is also connected to the load connections 10 connected to a precharge circuit, which here is also referred to as a drive train for driving the motor vehicle 2 is formed. The drive train thus forms the second subnet 4b of the electrical system 4 , The second subnet 4b has a DC voltage source 20 which, for example, provides a voltage of 12 V. For preloading the first subnet 4a a DC-DC converter is provided, which converts the voltage provided by the DC voltage source to that for operating the first sub-network 4a provided voltage changes, so here converts up (increases).

In 2 is the electrical system 4 shown comparatively in detail, only the battery for the purpose of an improved overview 10 , as well as the switch 14 with connected control unit 12 of the first subnet 4a is shown. Between the load connections 8th is an inverter 16 with three bridge branches 18 connected. Each of the bridge branches 18 has two switches connected in series 22 on which in the configurations of the 2 and 3 are designed as self-locking n-channel MOSFET semiconductor switches. Between the switches 22 is a center tap 24 provided (switched). Furthermore, the bridge branches 18 parallel to each other between the load connections 10 switched, in other words the load connections 10 , the two switches 22 one of the bridge branches 18 as well as the assigned center tap 24 connected in series. In a current path 26 between one of the center taps 24 the bridge branches 18 and one of the load connections 10 is one as a coil 28a trained inductance 28 as well as the DC voltage source 20 connected in series. The phase connection (positive pole, (+) - pole) is the DC voltage source 20 over the coil 28a with the inverter 16 connected. The ground connection (minus pole, (-) pole) of the DC voltage source is corresponding 20 with the corresponding load connection 10 connected.

There is also a switch 32 in the current path 26 switched, by means of which the DC voltage source 20 as well as the coil 28a can be switched on or off. Furthermore, there is between the load connections 10 parallel to the bridge branches 18 of the inverter 16 a capacitor 30 connected. By means of this and by means of as a coil 28a trained inductors 28 as well as by means of that bridge branch 18 of the inverter 16 , at its center tap 24 the the inductance 28 having current path 26 is connected, an inductive DC-DC converter designed as a step-up converter is formed. In other words, the capacitor works 30 , the inductors 28 as well as the switches 22 of the corresponding bridge branch 18 as a step-up converter for the DC voltage source 20 , So are (terminal) connections 33 the DC voltage source 20 connected to the DC converter. The capacitor is used 30 as a so-called charging capacitor, the voltage of the capacitor across the load connections 10 as (output) voltage U of the second subnet 4b on the first subnet 4a is applied.

Those designed as MOSFET switches 22 the bridge branches 18 between the respective center tap 24 and that with the ground connection of the DC voltage source 20 connected load connection 10 are connected to the center tap on the drain side 24 and source side to this load connection 10 connected. The other switches 22 the bridge branches 18 are on the source side to the center tap and on the drain side to the other load connection 10 connected.

The body diodes 34 the switch designed as a self-locking n-channel MOSFET 22 prevent the capacitor from being discharged 30 about the inductance 28 ,

To control the switches 22 shows the electrical system 4 a control unit 36 on. This is the switch with control inputs 22 connected. For the purpose of an improved overview, here is only the connection of the control unit 36 with the control input (gate) of the switches forming the DC-DC converter 22 shown. The other switches are also not shown 22 of the inverter 16 as well as the switch 32 with the control unit 36 connected. The control unit 36 is according to the statements of 2 and 3 one to the control unit 12 separate control unit, in a variant not shown, however, is the control unit 36 into the control unit 12 integrated.

The voltage U depends on the switching behavior of the switches 22 , This is done by means of the control unit 36 that switch 22 of the bridge branch forming the DC voltage converter 18 what switch 22 between the center tap 24 and that to the ground connection (negative pole) of the DC voltage source 20 connected load output 10 is switched in such a way that the voltage U , at least on average over time, to a predetermined voltage value U _target is set. For the purpose of preloading the first subnet 4a corresponds to the tension U to operate the first subnet 4a provided voltage. For this is a pulse width of this switch 22 modulated accordingly, in particular a duty cycle set accordingly. By means of the DC-to-DC converter designed as step-up converter, the voltage U at the load outputs 10 here is set to a value greater than that of the DC voltage source 20 provided voltage is.

For the purpose of better identification, the conductors (connections) between the components forming the DC-DC converter are shown in broken lines. The conductors between the components are therefore not interrupted, but rather connect the components to one another electrically (galvanically).

In summary, the DC voltage migrates using the inverter 16 and by means of the DC voltage source 20 formed, which are already part of the drive train. The DC-DC converter is therefore advantageously not an additional one in the motor vehicle 2 component to be inserted.

3 shows an alternative embodiment of the electrical system 4 , At the center tap 24 every bridge branch 18 is a (excitation winding) phase winding 38 an electrical machine designed as a three-phase motor 40 connected. The three phase windings are shown schematically simplified 38 connected with each other. For example, a delta connection or a star connection is used for this. In addition, is in each of the phase windings 38 each represents a change over time of a current by means of a circle, by means of which a torque for driving the motor vehicle during normal operation of the three-phase motor 2 is produced.

The DC voltage source 20 is with its phase connection with one of the phase developments 35 , here the middle one, connected. The inductance 28 the DC-DC converter designed as a step-up converter is by means of the inductors 28b the phase winding 38 to which the phase connection of the DC voltage source 20 is connected, and by means of an inductor 28b one of the other two phase windings 38 according to the circuit or the control of the switches 22 of these two phase windings 38 assigned bridge branches 18 educated. In summary, the inductance 28 the DC-DC converter designed as a step-up converter by means of inductors 28b of the electrical machine 40 educated. The switch is analogous 32 between the DC voltage source 20 and inductance 28b connected.

The 4 shows in a flowchart a process flow of a method for operation of the electrical system 4 , Here the tension U at the load connections 10 to a predetermined voltage value U _target set (step e ). This is done by the DC voltage source 20 provided a tension what as a step B referred to as. Here the switch 32 switched on (closed) and the DC voltage source 20 thus switched on. The switches 22 are also controlled in such a way that these together with the capacitor 30 and together with the inductance 28 as a step-up converter for the DC voltage source 20 act (step A ). By means of the step-up converter that from the DC voltage source 20 provided voltage is converted up (raised) so that the (output) voltage U the setpoint U _target corresponds to what as a step W is designated. This is the capacitor 30 due to the induced voltage and the voltage of the DC voltage source 20 loaded accordingly. The set voltage U becomes the preload of the first subnet 4a (step V ).

The desk 32 is also switched off (open). This is how the (normal) operation of the inverter is influenced 16 , in particular for generating the rotating field of the electrical machine 40 , avoided. This takes place either after the voltage has been increased U to the setpoint U _target at the end of the step W or preferably after precharging the first subnet 4a (Step V ).

The invention is not restricted to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by a person skilled in the art without departing from the subject matter of the invention. In particular, all of the individual features described in connection with the exemplary embodiments can also be combined with one another in other ways without departing from the subject matter of the invention.

LIST OF REFERENCE NUMBERS

2

motor vehicle

4

Electrical system

4a, b

first or second subnet

6

consumer

8th

battery

10

load connection

12

control unit

14

switch

16

inverter

18

bridge branch

20

DC voltage source

22

(Semiconductor) switch

24

center tap

26

Current path

28

inductance

28a

Kitchen sink

30

capacitor

32

switch

33

DC voltage source connections

34

body diode

36

control unit

38

phase winding

40

electrical machine

A

Activate the switches

B

Provide a tension

e

To adjust

U

tension

U _target

voltage value

V

subpoena

W

upconverting

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for better information for 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.

Patent literature cited

• EP 2786891 A1 [0005]

Claims (10)

Electrical vehicle electrical system (4) for a motor vehicle (2), comprising - an inverter (16) with at least one bridge branch (18), which has two series-connected switches (22) and a center tap (24) between the switches (22), two load connections (10), the bridge branch (18) of the inverter (16) being connected in series between them, - an inductance (28) and. in a current path (26) between the center tap (24) and one of the load connections (10) a DC voltage source (20) for setting a voltage (U) at the load connections (10) to a predetermined voltage value (U _target ) are connected in series. Electrical system (4) after Claim 1 , characterized in that the inductance (28) is that of an electrical machine (40) or a separate coil (28a). Electrical system (4) after Claim 2 , characterized in that - the inverter (16) has three bridge branches (18), each of the bridge branches (18) comprising two series-connected switches (22) and a center tap (24) between the switches (22), - at the Center taps (24) each have a phase winding (38) of the electrical machine (40) connected, and - the direct voltage source (20) being connected to one of the center taps (24). Electrical system (4) according to one of the Claims 1 to 3 , characterized by a capacitor (30) connected in parallel to the bridge branch (18) as a charging capacitor for setting the voltage (U) at the load connections (10). Electrical system (4) according to one of the Claims 1 to 4 , characterized in that the switches (22) of the bridge branch (18) are designed as semiconductor switches, in particular as self-locking n-channel MOSFETs. Electrical system (4) according to one of the Claims 1 to 5 , characterized by a control unit (36) for actuating the switches (22) of the or each bridge branch (18). Method for operating an electrical system (4) according to one of the Claims 1 to 6 , wherein voltage (U) at the load connections (10) of the vehicle electrical system (4) is set to a predetermined voltage value (U _target ). Procedure according to Claim 7 , wherein a voltage provided by the DC voltage source (20) is converted, in particular up-converted or stepped up. Procedure according to Claim 7 or 8th The switches (22) of the inverter (16) are controlled in such a way that they and the capacitor (30) and the inductor (28) act as a DC voltage converter, in particular as a step-up converter, for the DC voltage source (20). Electrically driven motor vehicle (2) with an electrical system (4) according to one of the Claims 1 to 6 ,

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