DE102013205869B4 - Vehicle with a polyphase machine - Google Patents

Abstract

Vehicle with a 2xN-phase electric machine, with a first partial on-board power supply system (BN1), which has a first nominal DC voltage level, and with a second partial on-board power supply system (BN2), which has a second nominal DC voltage level, the electric machine having a rotor, a common stator system (1 ) with a first N-phase winding system (1a) and a second N-phase winding system (1b), the first partial power system comprises an intermediate circuit capacitor (3), a first inverter (2a) and a second inverter (2b), the first winding system the first inverter and the second winding system are assigned to the second inverter,
- the first N-phase winding system is designed in a star connection,
- the second N-phase winding system is designed in a star connection, and
- at least one star point of a winding system can be electrically connected to the higher potential of the second partial on-board energy system by a transfer circuit, characterized in that
- the transfer circuit can be operated with pulse width modulation.

Description

The invention relates to a vehicle with a 2xN-phase electrical machine, with a first partial on-board power supply system which has a first nominal DC voltage level, and with a second partial on-board power supply system which has a second nominal DC voltage level, the electric machine having a rotor, a common stator system with a first N -phase winding system and a second N-phase winding system, the first partial power system comprises an intermediate circuit capacitor, a first inverter and a second inverter, the first winding system is assigned to the first inverter and the second winding system is assigned to the second inverter.

Typically, components in a vehicle that consume electrical energy are supplied by an on-board power system with a nominal voltage of 14 volts. A secondary 12 V energy storage device, which takes on the function of an energy source or the function of an energy sink in the on-board network depending on the operating situation, and a 14 V generator are designed to provide an electrical output of 2-3 kW in the vehicle.

If several consumers with higher power requirements are integrated into the vehicle's on-board network, the on-board network can have two partial on-board energy networks. A DC controller then transfers electrical power between the two partial energy systems. The electric machine, which can also be operated by a motor in a vehicle with an electrified drive train, has the function of an electrical energy source or sink in the vehicle in addition to at least one energy storage device for each partial on-board energy network. Such an electrical system topology is in writing, for example DE 102 44 229 A1 shown.

DE 10 2012 203 528 A1 discloses a vehicle with an electric machine and a method for operating the same, with two stators being assigned to a rotor of an electric machine. The star point of the first stator system can be connected to the higher potential of a second sub-board network, which is assigned to the second stator system, via a transfer circuit.

It is an object of the invention to provide an improved vehicle with a 2xN-phase electrical machine, with a first partial on-board power supply system which has a first nominal DC voltage level, and with a second partial on-board power supply system which has a second nominal DC voltage level, the electric machine having a rotor, a common Stator system with a first N-phase winding system and a second N-phase winding system, the first partial power system comprises an intermediate circuit capacitor, a first inverter and a second inverter, the first winding system is assigned to the first inverter and the second winding system is assigned to the second inverter .

This task is solved by a vehicle according to claim 1. Advantageous embodiments and developments of the invention result from the dependent claims.

According to the invention, the first N-phase winding system is designed in a star connection, the second N-phase winding system is designed in a star connection, and at least one star point of a winding system can be electrically connected in a pulse width modulated manner using a transfer circuit with the higher potential of the second partial on-board energy system.

The expression 2xN means that the machine has two N-phase winding systems.

According to a preferred embodiment of the invention, the transfer circuit can be switched on or off permanently. In addition, according to the invention, the transfer circuit can be operated with pulse width modulation.

This means that the transfer circuit can assume a “permanent off” switching state or a “permanent on” switching state.

It is advantageous if the first winding system and the second winding system of the electrical machine each have three phases and the two winding systems are electrically offset from one another by essentially 30°.

According to a further embodiment variant of the invention, the two star points of the respective N-phase winding system can be connected to the higher potential of the second partial energy system via a common switch and the two inverters can be controlled in a phase-offset and pulse width modulated manner.

This ensures that a current ripple of a current flowing between the two partial on-board energy systems is reduced. A current ripple is understood to be an alternating component superimposed on the average direct current, which comes about because the inductance effective in the electrical machine is subjected to a pulse-width-modulated voltage. The height of the current ripple depends on the duty cycle pulse width modulated voltage, the clock frequency of the inverter, the level of the inductance and the voltage difference across the inductance.

For a buck converter, the current ripple can be specified as follows: $$\mathrm{<figure-callout\; id="0"\; label="\Delta \; I"\; filenames="DE102013205869B4\_0007.png"\; state="\{\{state\}\}">\Delta </figure-callout>}{I}_{}{}_0=\frac{U_e-U_a}{L}\cdot D\cdot t_s$$

For the buck converter, the duty cycle is defined as $$D=\frac{U_a}{U_e}$$

wobei hier das Tastverhältnis als $$D=\frac{U_a-U_e}{U_a}$$

definiert ist. Unter Annahme gleicher Parameter ergibt sich in beiden Fällen der gleiche Stromrippel.The current ripple applies to the step-up converter $$\mathrm{\Delta }{I}_{}$$$${}_0=\frac{U_e}{L}\cdot D\cdot t_s$$

where here the duty cycle is $$D=\frac{U_a-U_e}{U_a}$$

is defined. Assuming the same parameters, the same current ripple results in both cases.

Furthermore, it may be that the two star points of the two N-phase winding systems are electrically connected and can each be connected to the higher potential of the second partial on-board energy network via a switch, and the two inverters can be controlled in a phase-offset and pulse width modulated manner in order to create a current ripple between the two partial on-board energy systems to reduce the current flowing. A phase offset occurs, for example, because the control unit supplies the pulse width modulated control signals to the two inverters with a time delay.

It is particularly advantageous if the two star points of the two N-phase winding systems are electrically connected and can be connected to the higher potential of the second partial energy system via a half bridge, and at least one of the two inverters and / or the half bridge can be controlled in a phase-offset and pulse width modulated manner in order to achieve a To reduce current ripple of a current flowing between the two partial energy systems.

This means that only the half bridge or alternatively only one of the two inverters or the half bridge and one of the two inverters in combination are controlled in a phase-offset and pulse width modulated manner.

According to a particularly preferred variant of the invention, the respective star point of the respective N-phase winding system can be connected to the higher potential of the second partial on-board energy system via a half bridge and at least one of the two inverters and / or at least one of the half bridges can be controlled in a phase-offset and pulse width modulated manner to reduce a current ripple of a current flowing between the two partial energy systems.

It is also particularly advantageous if the first inverter has three high-side switches (HS1, HS2, HS3) and three low-side switches (LS1, LS2, LS3), and the second inverter has three high-side switches (HS4 , HS5, HS6) and three low-side switches (LS4, LS5, LS6), the three high-side switches of the first inverter and the three low-side switches of the first inverter can be controlled with pulse width modulation, the three high-side switches Side switch of the second inverter and the three low-side switches of the second inverter can be controlled in a pulse-width-modulated manner, and the electrical machine can be controlled as a motor or generator either when the transfer circuit is active or inactive or in a mixed operation by means of pulse-width-modulated control of the high-side switches and low-side switches. Side switch of the first inverter and the second inverter can be operated.

There are also advantages if the first nominal voltage level exceeds the second nominal voltage level in the direction of a higher nominal voltage level, and the electric machine can be operated as a DC step-down converter from the first partial on-board power supply system and to the second partial on-board power supply system both when the rotor is stationary and when the rotor is rotating.

The first nominal voltage level can also exceed the second nominal voltage level in the direction of a higher nominal voltage level and the electrical machine can be operated as a direct current step-up converter from the second partial on-board energy network to the first partial on-board energy network both when the rotor is stationary and when the rotor is rotating.

Furthermore, the rotor can be short-circuited if an excitation winding is present.

• Ein Fahrzeug mit einem 12 Volt-Teilenergiebordnetz und mit einem 48 Volt-Teilenergiebordnetz kann umgesetzt werden beispielsweise mit einem riemengetriebenen 48 Volt-Startergenerator und einem Gleichstrom-Gleichstrom-Steller zwischen den beiden Teilenergiebordnetzen.

The invention is based on the considerations set out below:

• A vehicle with a 12 volt partial on-board energy network and with a 48 volt partial on-board energy network can be implemented, for example, with a belt-driven 48 volt starter generator and a DC-DC converter between the two partial on-board energy systems.

Alternatively, a starter generator with two voltage levels can be used, ie an electrical machine with a common stator system and 2 x N-phase winding systems, whereby each partial on-board power system is assigned a winding system and the star points of the two winding systems can be connected via a switch. In this way, power can be transferred between the two partial energy systems without the need for a separate DC-DC converter, which has a beneficial effect on costs, weight and installation space.

The disadvantage of this, however, is that part of the power of the electrical machine is assigned to the 12-volt partial energy system and is not fully charged as recuperation power on the 48-volt side, for example in an energy storage device there such as a 48-volt lithium-ion battery can. If the assigned power is divided between the two partial on-board energy systems of, for example, 75% to the 48-volt partial on-board energy network and 25% to the 12-volt partial on-board energy network, half of the silicon semiconductor area required in the inverters for current-carrying capacity, which is designed, for example, using MOSFET technology, for the 12 volt partial energy on-board network (25%). With the same level of phase currents, the current ripple load of two intermediate circuit capacitors (one intermediate circuit capacitor in each partial power supply system), each of which is assigned to a 3-phase machine, exceeds the current ripple load of a 2 x 3-phase electrical machine with only one voltage level in which the two 3 -phase windings are shifted by 30° to each other. This means that the capacity of the intermediate circuit capacitors must be chosen to be high.

In order to improve the operation of a starter generator with two voltage levels, it is proposed, based on a 6-phase 48 volt starter generator with two 3-phase winding systems connected in a star connection, the electrical phases of which are each offset by 30 ° to one another, via a star point switch with the 12 volt partial on-board power supply system.

The star point switch can be used when stationary (0 revolutions of the rotor of the electrical machine per minute) or during operation (> 1500 revolutions of the rotor of the electrical machine per minute) either by permanently switching on or by pulse width modulated control, if necessary also in interleaved operation, i.e. phase-shifted control of the star point switches or the two B6 converters, which are assigned to the respective winding systems, electrical power can be transferred from the 48 volt partial on-board energy network to the 12 volt partial on-board energy network or vice versa.

In comparison to a system with a starter generator with two voltage levels, i.e. with two winding systems, whereby an electrical winding system is assigned to each partial on-board energy network and either the star points of the two winding systems can be connected to one another via a switch or the star point of the winding system, which is assigned to the partial on-board energy network with a higher voltage can be connected to the higher potential of the lower voltage on-board power supply system, there is the possibility of a smaller volume of the intermediate circuit capacitors due to a lower ripple current load, a smaller semiconductor area and a higher convertible direct current-direct current power. This has an advantageous effect on costs, weight and installation space.

When recuperating, the full power of the electrical machine can always be made available in the 48 volt partial energy system, i.e. the recuperation performance can be maximized to benefit the energy efficiency of the vehicle.

Furthermore, in the event of a single error, e.g. a winding short, a winding break or a MOSFET error in the star point switch, half the conversion power is still available via the second star point switch.

The invention therefore shows a vehicle with a 2xN-phase machine, with a first partial on-board power supply system which has a first nominal DC voltage level, and with a second partial on-board power supply system which has a second nominal DC voltage level, the electric machine having a rotor, a common stator with a first N -phase winding and a second N-phase winding, the first partial on-board power supply system comprises a first and a second inverter with a common intermediate circuit capacitor, the first winding system is assigned to the first inverter and the second winding system is assigned to the second inverter, and the second partial on-board power supply system comprises an intermediate circuit capacitor .

The connection between the two partial on-board energy networks occurs via the two star points of the 2xN-phase machine and the higher potential of the second partial on-board energy network, either directly or optionally via one or more switches. The inverter can either be a common bridge circuit or designed as a multi-level inverter. A particularly advantageous embodiment of the electrical machine consists of 2x3-phase winding systems that are offset from one another by a certain electrical angle, particularly advantageously by 30°. This reduces the current ripple in the intermediate circuit capacitors sator, which is assigned to the two inverters in the partial energy system 1, is significant.

Both winding systems are designed in a star connection and a transfer circuit connects both star points of the two winding systems with the higher potential of the second partial on-board energy network.

This means that both star points of the two winding systems can be directly electrically coupled to the higher potential of the second partial energy system.

According to a preferred embodiment of the invention, the transfer circuit comprises a first diode and a second diode, which are connected in opposite directions and in series.

Furthermore, the transfer circuit comprises a first switch which is connected in parallel with the first diode or alternatively a second switch which is connected in parallel with the first diode.

It is also particularly advantageous if the transfer circuit comprises the first switch, which is connected in parallel with the first diode, and the second switch, which is connected in parallel with the second diode.

The diodes connected in opposite directions ensure that when the first switch is open and/or when the second switch is open, the direct electrical coupling between the star point of the respective winding system and the higher potential of the second partial on-board energy network is ineffective. When the first switch is closed and/or when the second switch is closed, there is a direct electrical connection between the star point of the respective winding system and the higher potential of the second partial energy system in the form of a very low-resistance connection through a series connection of two closed switches or a series connection of a switch and a diode .

A further variant of the invention is that both inverters advantageously have a half bridge for each N phase of the machine, each with a high-side switch and a low-side switch. Each switch of a half bridge can be controlled in a pulse-width modulated manner, so that the electrical machine is either completely motoric or completely generator-like or in a pulse-width-modulated control of the high-side switches and the low-side switches of the first inverter and the second inverter, both when the star point connection is open or closed can be operated in mixed operation. The low-side switches and high-side switches each have a low-side diode and a high-side diode connected in parallel.

This means that the machine can be used as a generator or as a motor with regard to the partial on-board energy network. When operating as a generator, the partial energy on-board network 1 is supplied with electrical energy via at least one winding system of the machine as a result of a torque applied to the rotor from outside (e.g. from an internal combustion engine of the vehicle). When operating as a motor, electrical energy is taken from the partial energy on-board network 1 via at least one winding system and converted into rotational energy of the rotor, which is tapped from the rotor from outside (e.g. from a belt-driven consumer of the vehicle) as torque.

It is particularly advantageous if the first nominal voltage level exceeds the second nominal voltage level in the direction of the voltage level relative to a reference voltage in the vehicle, e.g. an electrical mass of the vehicle that is common to the two partial on-board energy systems, and the electric machine acts as a DC voltage step-down converter between the first partial on-board energy network when the rotor is at a standstill and can be operated to the second partial energy on-board network.

The electric machine can be operated as a bidirectional DC-DC converter in that the star point connection to the partial on-board power system 2 is closed and at least one of the star point currents is regulated to a positive or negative value via the control unit and the active inverter is controlled in a pulse width modulated manner.

In addition, if there is an excitation winding on the rotor of the electrical machine, it can be electrically short-circuited if necessary.

• 1: Fahrzeug mit elektrischer Maschine, Gleichstromsteller und zwei Teilenergiebordnetzen (Stand der Technik)
• 2: Fahrzeug mit elektrischer Maschine und einem Sternpunktschalter, welcher mit zusammengeschaltetem Sternpunkt der 2xN-phasigen Maschine verbunden
• 3: Fahrzeug mit elektrischer Maschine und zwei Sternpunktschaltern, welche mit jeweils einem Sternpunkt der 2xN-phasigen Maschine verbunden
• 4: Fahrzeug mit elektrischer Maschine und mit nachgeschalteter Halbbrücke, welche mit zusammengeschaltetem Sternpunkt der 2xN-phasigen Maschine verbunden
• 5: Fahrzeug mit elektrischer Maschine und mit zwei nachgeschalteten Halbbrücke, mit jeweils einem Sternpunkt der 2xN-phasigen Maschine verbunden
• 6a/b: Beispielhafte Ausführungsformen des Schalters/der Schalter nach den 2 bis 5

Preferred exemplary embodiments of the invention are described below with reference to the accompanying drawings. This results in further details, preferred embodiments and further developments of the invention. In the figures, the same reference numbers indicate the same technical features. Show in detail schematically

• 1 : Vehicle with electric machine, DC controller and two partial energy systems (state of the art)
• 2 : Vehicle with an electric machine and a star point switch, which is connected to the interconnected star point of the 2xN-phase machine
• 3 : Vehicle with electric machine and two star point switches, each with connected to a star point of the 2xN-phase machine
• 4 : Vehicle with an electric machine and a downstream half bridge, which is connected to the interconnected star point of the 2xN-phase machine
• 5 : Vehicle with an electric machine and two downstream half bridges, each connected to a star point of the 2xN-phase machine
• 6a /b: Exemplary embodiments of the switch(es) according to the 2 to 5

For a vehicle with two partial on-board energy systems (dual-voltage on-board electrical system) at two different nominal voltage levels, according to the state of the art, at least four components may essentially be required in addition to the two partial on-board energy systems themselves (see 1 ). These are an N-phase electrical machine (1) - preferably in a star connection, but other designs are also possible - and a DC voltage regulator (4) between two partial on-board power systems (BN1, BN2). The electrical machine can consist of two 3-phase winding systems, which can be constructed essentially identically. The two winding systems can also be connected to one another at a certain electrical angle.

The on-board electrical system (BN2) can, for example, be a conventional 12 V on-board electrical system and the on-board electrical system (BN1) can be an on-board electrical system with a higher nominal voltage level. Alternatively, the on-board electrical system (BN1) and the on-board electrical system (BN2) can have a comparable nominal voltage level of, for example, 400 V, if different energy storage devices, for example a lithium-ion battery and a double-layer capacitor, are combined with one another. Both on-board electrical systems have a higher electrical potential, which is essentially determined by the two nominal voltage levels, and a lower electrical potential, which is common to both on-board electrical systems and is possibly connected to the ground of the vehicle. The actual voltage levels of the higher electrical potentials of the two on-board electrical systems can deviate from the respective nominal voltage levels of the two on-board electrical systems at any time of operation.

The DC voltage controller enables the uni- or bi-directional transfer of power or energy between the two on-board electrical systems, regardless of the state of the electrical machine.

According to the state of the art, an N-phase electrical machine, e.g. a 6-phase machine with two three-phase windings in a star connection, can be used as the electrical machine. Each of the two 3-phase winding systems is operated via an inverter (2a, 2b) and a common intermediate circuit capacitor (3). The second partial on-board power supply system optionally has a smoothing capacitor (3').

2 shows a vehicle according to the invention with the electric machine (1) and a common star point switch (4), via which the star points of the 2xN-phase machine (1a, 1b) are connected to the partial on-board energy supply system (BN2).

This topology represents the simplest type of step-up/step-down converter. When the electric machine is rotating, however, the amount of power that can be transferred depends heavily on how high the two inverters, which are assigned to the partial on-board energy network 1, are already controlled, for example by one to generate positive or negative torque.

The advantage of the invention is that power can be transferred between the two on-board electrical systems via the electrical machine and the inverters used to operate the electrical machine and a circuit that can be easily integrated into the vehicle. This offers the advantage that without using a DC controller (4) (as in 1 shown) Energy can be transferred from one partial energy on-board network of the vehicle to the other partial energy on-board network of the vehicle without the need for the electrical machine to be in operation.

Another particular advantage is the ability to adjust an energy transfer direction (buck and/or boost operation) based on the design of the transfer circuit. This can, for example, consist of a switch that connects the partial on-board power supply (BN2) to the interconnection of the two star points of the N-phase machine. This can be advantageous if there is no electrical angle between the two N-phase winding systems and it is assumed that the star point voltage of both windings is essentially the same at all times.

3 shows a further embodiment of the vehicle with the electrical machine (1) and two star point switches (4a, 4b), which are each connected to a star point of the 2xN-phase machine (1a, 1b) and the partial on-board energy network (BN2).

The basic functionality of this topology is the same as the previous one 2 , but offers the advantage of redundancy.

This means that each star point of the N-phase machine can be separately connected to its own star point switch and the higher potential of the second partial on-board energy network. This can be advantageous if there is an electrical angle between the two N-phase winding systems and it cannot be guaranteed that the star point voltage of both windings is essentially the same at all times. Another advantage is the possibility of still being able to transfer half of the total power that can be transferred between the partial on-board energy systems if a winding system fails.

In addition, by operating the inverters of the two N-phase windings in a phase-shifted manner, the current ripple of the entire star point current that flows between the partial on-board energy systems 1 and 2 can be reduced, which means that the intermediate circuit capacitor (3 ') of the partial on-board energy network can be made smaller. If necessary, the star point switch can also be controlled by the control unit using pulse width modulation in order to further reduce the current ripple if necessary.

Further embodiments of the transfer circuit are in 4 in the form of a half bridge (switch 4 and switch 4`) and in 5 shown in the form of two half bridges (switches 4a, 4a`, 4b, 4b`). The advantage here is the possibility of using pulse-width modulated control of the switches (4) and (4') even with relatively low star point voltage and high voltage in the partial energy on-board network (BN2). 4 or the switches (4a) and (4a`) as well as the switches (4b) and (4b`) in 5 to realize a step-up converter operation.

In the 5 The topology shown additionally offers the degree of freedom of phase-shifted operation between the two half-bridges attached to the star points of the N-phase winding systems, whereby the current ripple of the total star point current that flows between the partial on-board energy systems (BN1) and (BN2) can be further reduced.

6a shows embodiments of the switches (4), (4`), (4a), (4b) from the 2 to 5 .

Variant 1 represents the simplest implementation option for the star point switch with just one switch and parallel diode, which can be used if it is ensured that the potential of the star point is always higher than the higher potential of the on-board electrical system. Variant 2 is particularly advantageous with 2 switches and diodes directed in opposite directions, which ensures that the voltage is blocked on both sides under any circumstances and enables both step-up and step-down converter operation. Variants 3 and 4 represent further options for a double-sided blocking switch if energy transfer in only one direction is required.

6b shows embodiments of the switches (4a`) and (4b`). 5 .

The simplest way to implement the freewheeling switch is the diode, which, however, results in gap operation at low current. The design as a switch with a parallel diode solves this problem and also has the advantage that the forward losses when the switch is closed are lower than when the diode conducts.

Reference symbol list

1

N-phase machine, preferably in a star connection

2a

Inverter for first winding system

2 B

Inverter for second winding system

3

Common intermediate circuit capacitor for BN1, assigned to inverters 1 and 2

3'

Smoothing capacitor, assigned to BN2

4, 4`, 4a, 4a`, 4b, 4b'

Switch (each)

40

DC/DC converter for energy transfer between partial energy on-board network 1 and 2

5

Control unit for controlling the inverter

6

Energy storage in the partial energy on-board network 1

6'

Energy storage in the partial energy on-board network 2

7

Consumers in BN1

7'

Consumers in BN2

Claims (11)

Vehicle with a 2xN-phase electrical machine, with a first partial on-board energy network (BN1), which has a first nominal DC voltage level, and with a second partial on-board energy network (BN2), which has a second nominal DC voltage level, wherein the electrical machine comprises a rotor, a common stator system (1) with a first N-phase winding system (1a) and a second N-phase winding system (1b), the first partial on-board power supply system includes an intermediate circuit capacitor (3), a first inverter (2a) and a second inverter (2b), the first winding system is assigned to the first inverter and the second winding system is assigned to the second inverter, - the first N-phase winding system is designed in a star connection, - that second N-phase winding system is designed in a star connection, and - through a transfer circuit at least one star point of a winding system can be electrically connected to the higher potential of the second partial on-board energy network, characterized in that - the transfer circuit can be operated with pulse width modulation. Vehicle after Claim 1 , characterized in that - the transfer circuit can be switched on permanently, and - the transfer circuit can be switched off permanently. Vehicle after Claim 1 or 2 , characterized in that - the first winding system and the second winding system of the electrical machine each have three phases and - the two winding systems are electrically offset from one another essentially by 30°. Vehicle according to one of the preceding claims, characterized in that - respective star points of the respective N-phase winding system can be connected to the higher potential of the second partial on-board energy network via a switch (4a, 4b), and - the two inverters (2a, 2b) are phase-offset and can be controlled in a pulse width modulated manner in order to reduce a current ripple of a current flowing between the two partial on-board power systems. Vehicle according to one of the Claims 1 until 3 , characterized in that - star points of the two N-phase winding systems are electrically connected and can be connected to the higher potential of the second partial energy system via a common switch (4), and - the two inverters (2a, 2b) can be controlled in a phase-offset and pulse width modulated manner to reduce a current ripple of a current flowing between the two partial energy systems. Vehicle according to one of the Claims 1 until 3 , characterized in that - star points of the two N-phase winding systems are electrically connected and can be connected to the higher potential of the second partial on-board energy system via a half bridge (4, 4`), and - at least one of the two inverters (2a, 2b) or the half bridge can be controlled in a phase-shifted and pulse-width modulated manner in order to reduce a current ripple of a current flowing between the two partial on-board power systems. Vehicle according to one of the Claims 1 until 3 , characterized in that - a respective star point of the respective N-phase winding system can be connected to the higher potential of the second partial energy system via a half bridge (4a, 4a 'and 4b, 4b`), and - at least one of the two inverters (2a, 2b) or at least one of the half bridges can be controlled in a phase-offset and pulse width modulated manner in order to reduce a current ripple of a current flowing between the two partial on-board power systems. Vehicle according to one of the preceding claims, characterized in that - the first inverter has three high-side switches (HS1, HS2, HS3) and three low-side switches (LS1, LS2, LS3), - the second inverter has three high -Side switches (HS4, HS5, HS6) and three low-side switches (LS4, LS5, LS6), - the three high-side switches of the first inverter and the three low-side switches of the first inverter are pulse width modulated can be controlled, - the three high-side switches of the second inverter and the three low-side switches of the second inverter can be controlled in a pulse width modulated manner, - the electrical machine can be controlled by a motor or generator either when the transfer circuit is active or inactive or in a mixed operation by pulse width modulated control High-side switch and low-side switch of the first inverter and the second inverter can be operated. Vehicle according to one of the preceding claims, characterized in that - the first nominal voltage level exceeds the second nominal voltage level in the direction of a higher nominal voltage level, - the electric machine both when the rotor is stationary and when the rotor is rotating acts as a direct current step-down converter from the first partial on-board energy network and to the second partial on-board energy network (BN2) is operable. Vehicle according to one of the preceding claims, characterized in that - the first nominal voltage level, the second nominal voltage level in the direction of higher nominal voltage voltage position exceeds, and - the electric machine can be operated as a DC step-up converter from the second partial on-board energy network (BN2) to the first partial on-board energy network (BN1) both when the rotor is stationary and when the rotor is rotating. Vehicle according to one of the preceding claims, characterized in that the rotor can be short-circuited in the presence of an excitation winding.

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