DE102010019151B4 - Method and device for energy transmission in a motor vehicle - Google Patents

Abstract

Device for energy transmission in a motor vehicle, the motor vehicle having an on-board network, the on-board network having at least one low-voltage area (2) with a first voltage level, the device (1) having at least one electric machine (6), a converter assigned to the electric machine (6). (7), at least one intermediate circuit capacitor (CZK), at least one energy store assigned to the low-voltage range, at least one element for voltage conversion and at least one control unit, the electric machine (6) being operable in motor mode or generator mode, the converter (7) has at least one half-bridge with two power switches (S1, S2, S3, S4, S5, S6), wherein a section between the power switches (S1, S2, S3, S4, S5, S6) has a first supply path with a terminal (K1, K2, K3) of the electric machine (6) is electrically connected, the element for voltage conversion at least at least two power switches (S1, S2, S3, S4, S5, S6, S7, S8) and at least one inductor (L), the power switches of the voltage conversion element being the power switches (S1, S2, S3, S4, S5, S6 ) of the at least one half-bridge of the converter (7), wherein the at least one inductance (L) of the element for voltage conversion in a second supply path that connects the low-voltage range (2) and that between the power switches (S1, S2, S3, S4, S5 , S6) electrically connects the half-bridge portion of the half-bridge, the second supply path being different from the first supply path, characterized in that the device (1) has a unit (10) designed to determine at least one mean phase voltage (UP1M) a mean phase voltage (UP1M) of the converter (7) at least depending on a desired, in the low voltage range (2) into or out of the low voltage range h (2) to determine power (PNV) to be transmitted, the device (1) further having at least one unit (12) designed to determine at least one motor voltage (US1, US2, US3) of the electric machine (6) to determine a motor voltage (US1, US2, US3) of the electric machine (6) at least as a function of a desired electrical power (PEM) of the electric machine (6), the device (1) further having at least one unit (13), which is designed to determine at least one target phase voltage (UP1, target, UP2, target, UP3, target) a target phase voltage (UP1, target, UP2, target, UP3, target) of the converter (7) at least as a function the mean phase voltage (UP1M) and the motor voltage (US1, US2, US3), the control unit switching the circuit breakers (S1, S2, S3, S4, S5, S6) of the converter (7) depending on the target phase voltage (UP1, target, UP2, target, UP3, target) controls.

Description

The invention relates to a method and a device for energy transmission in a motor vehicle.

In modern motor vehicles, there is often a need to supply electrical loads with a supply voltage that can have different voltage levels for different loads. As a rule, supply voltages of different voltage levels are made available by different energy stores, for example batteries. Thus, it is known to provide low-voltage batteries with an output voltage of 12 V (conventional vehicle electrical system batteries) for a conventional low-voltage system. These are used to supply power to control units in the vehicle, for example, which are designed for a voltage level of 12 V. With the increase in control devices and electrical consumers, in particular electrical consumers with a high power requirement, in the vehicle, the idea was developed of integrating a so-called high-voltage battery, which has a higher output voltage, for example 42 V, than the low-voltage battery in the vehicle. As a result, e.g. a lower current is required for the same power requirement, which means that smaller cable cross-sections can be used. Here, the low-voltage battery and the high-voltage battery are generally formed separately.

In classic vehicles powered by internal combustion engines, there is also the problem that there are usually two differently designed electric motors for converting electrical energy from the vehicle electrical system battery into mechanical energy (motor operation) and for converting mechanical energy into electrical energy from the vehicle electrical system battery (generator operation). (e.g. a starter and an alternator) are required.

the DE 102 44 229 A1 discloses a generic power supply system equipped with a high voltage system and a low voltage system. The power supply system includes an AC motor suspended as a load on the high voltage system and driven by the high voltage power supply source. Further, the power supply system includes an inverter for controlling the supply of power to the AC motor. Further, the power supply system includes a low-voltage system supply path for applying a neutral point voltage of the AC motor to a low-voltage system load and a low-voltage system load for connecting to the low-voltage system supply path, wherein a voltage ratio of the low-voltage system to the high-voltage system is set to 1:2 to 1:4 .

the DE 198 57 645 A1 discloses an electrical system for an electric vehicle, comprising: a DC input circuit, a voltage inverter connected to the DC input circuit, to which an input voltage is applied from the DC input circuit and which generates a variable AC voltage of variable frequency, an AC motor having a plurality of windings whose each end is connected to an AC output terminal of the inverter while the other ends of the windings are connected together to form a neutral point of the motor windings, a variable voltage energy storage element connected between the neutral point and a connection point in the DC input circuit, and a DC power supply connected to the opposite Ends of the energy storage element is connected.

A generic device for energy transmission in a motor vehicle is known from WO 2007/123 884 A2.

A device for energy transmission in a motor vehicle is known from US 2007/0 200 521 A1, the element for voltage conversion being formed by two separate switching elements and a separate inductor.

The technical problem arises of creating a method and a device for energy transmission in a motor vehicle which, on the one hand, enable energy transmission with favorable efficiency and are designed cost-effectively, with energy transmission from a low-voltage range of the vehicle electrical system to the electric machine and/or other voltage ranges of the vehicle electrical system different voltage levels and an energy transfer from the electric machine in the low-voltage range, in particular to the on-board battery, and / or the other voltage ranges is made possible.

The solution to the technical problem results from the objects with the features of claims 1 and 6. Further advantageous configurations of the invention result from the dependent claims.

A device for energy transmission in a motor vehicle is proposed, the motor vehicle having an on-board electrical system, the on-board electrical system having at least one low-voltage range with a first voltage level. In this case, electrical consumers of the motor vehicle, in particular control units of the motor vehicle, are connected to the vehicle electrical system. The first voltage level can be 12 V, for example. The device also includes at least one electric machine and a converter assigned to the electric machine. The electric machine can be operated in motor mode or generator mode. In motor operation, the electric machine can be used, for example, as a starter for an internal combustion engine in the motor vehicle. In generator operation, the electric machine can be used, for example, as an alternator in an internal combustion vehicle. An operating voltage of the electric machine can be variable, in particular higher than 12V. The electrical machine is preferably designed as a three-phase electrical machine and the converter as a three-phase converter. In this case, the converter serves to generate an AC voltage with a desired frequency and a desired amplitude from a DC voltage during motor operation of the electric machine. In generator operation, the converter is also used to generate a DC voltage with a desired amplitude from an AC voltage generated by the electric machine.

Of course, a single-phase design of the electric machine, for example as a DC machine, is also conceivable.

The device according to the invention also includes at least one intermediate circuit capacitor. In this case, the intermediate circuit capacitor is preferably connected upstream of the converter, so that an operating or input voltage of the converter is equal to the intermediate circuit voltage drop across the intermediate circuit capacitor. The intermediate circuit voltage can also be variable, in particular the intermediate circuit voltage can be higher than 12V.

The device also includes at least one energy storage device assigned to the low-voltage range. This energy store can in particular be a battery or what is known as an on-board power supply battery. Without restriction, the energy store is referred to below as the vehicle electrical system battery. The vehicle electrical system battery is used here to supply energy to electrical consumers connected to the vehicle electrical system, in particular also to supply energy to the electric machine in motor operation. The vehicle electrical system battery is also used to store energy, in particular to store the electrical power generated by the electric machine in generator mode.

The device also includes at least one element for voltage conversion. The converter is electrically coupled to the low-voltage range, in particular to the vehicle electrical system battery, via the element for voltage conversion. In this case, the element for voltage conversion can be operated as a so-called step-down converter or as a so-called step-up converter. The element for voltage conversion is preferably a direct current converter (DC/DC converter).

The converter includes at least one half-bridge with two power switches, with a section of the half-bridge between the power switches being electrically connected to a terminal of the electric machine via a first electrical supply path. In this case, the power switches are in the form of MOSFETs or IGBTs, for example.

According to the invention, the element for voltage conversion also includes at least two circuit breakers. The element for voltage conversion also includes at least one inductor. In this case, an inductance is understood to mean an at least partially inductive component, for example a coil. According to the invention, the power switches of the voltage conversion element are the power switches of the at least one half-bridge of the converter. As a result, the element for voltage conversion is at least partially integrated into the converter.

The at least one inductance of the element for voltage conversion is arranged in a second supply path, which electrically connects the low-voltage area and the section of the half-bridge lying between the power switches of the half-bridge.

According to the invention, the second supply path is different from the first supply path. As a result, the at least one inductor is designed as an individual component, in particular as a component that is designed separately from an inductor of the electric machine. In contrast to DE 102 44 229 A1 and to DE 198 57 645 A1 According to the invention, an inductance of the element for voltage conversion is not formed by an inductance of the electric machine.

This advantageously means that when the electric machine is operating as a generator, circuit breakers of the element for voltage conversion can be controlled by a control unit in such a way that electrical energy generated by the electric machine is at least partially transferred to the low-voltage range, i.e. to the vehicle electrical system battery and/or to the low-voltage range consumer, is transferrable. Furthermore, the circuit breakers of the voltage conversion element can be controlled by the control unit during motor operation in such a way that energy in the low-voltage range, in particular electrical energy stored in the vehicle electrical system battery, can be at least partially transmitted to the electric machine.

In this case, the energy transmission is independent of voltage differences in the vehicle electrical system, ie also independent of voltage differences between the low-voltage range and an intermediate circuit voltage.

In motor operation, energy can be supplied to the electric machine from the vehicle electrical system battery in an advantageous manner. If the electric machine is used as a starter, e.g. In addition, the electric machine can take over the functionality of an alternator, ie a generator, in an equally advantageous manner, with electrical energy being able to be stored in the vehicle electrical system battery. The operating modes described (motor or generator operation) are made possible here by means of the element for voltage conversion. For example, high voltages generated by the electric machine in generator mode can be converted by means of the element for voltage conversion into an output voltage of the converter that is the same as the first voltage level. Likewise, voltages required for starting or motor operation of the electric machine can be converted from the first voltage level to a desired, in particular higher, voltage level by means of the voltage conversion element. This results in particular in a mode of operation of the electric machine that is favorable in terms of efficiency. Since the power switches of the element for voltage conversion are also power switches of at least one half-bridge of the converter, the result is a partially integrated design of the element for voltage conversion. As a result, production costs and installation space requirements can be minimized in an advantageous manner.

Especially when compared to the teaching of DE 102 44 229 A1 and the DE 198 57 645 A1 no star point tapping of the electric machine is necessary. This results in an advantageous manner in that electric machines with different motor circuits, eg delta circuits, can be operated in motor and generator mode by means of the device according to the invention. In a further advantageous manner, the comparison results in improved efficiency in DC voltage converter operation, hereinafter also referred to simply as converter operation, of the converter, since the at least one inductance of the element for voltage conversion can be optimized for converter operation.

A possible optimization is e.g. the use of ferrite as magnet material. Motor inductances, i.e. inductances of the electric machine, have to take into account the requirements for high forces or torques in their design. In particular, the material used for the motor inductors must be designed to suit high magnetic field strengths, which, for example, leads to the use of higher-loss iron as the magnet material. Such requirements advantageously do not exist in the design or dimensioning of the at least one inductance of the element for voltage conversion.

A control or regulation of the circuit breakers can also take place via a so-called control or regulation hierarchy with several levels. In this case, for example, a desired current intensity and/or current direction can be specified by the at least one inductance of the element for voltage conversion. The control unit or sub-units of the control unit determine an intermediate circuit voltage to be set by means of the voltage conversion element from the desired current intensity and/or current direction. From this, in turn, switching times of the power switches of the element for voltage conversion can be calculated. Likewise, the control unit or a sub-unit of the control unit can determine a desired terminal differential voltage and/or a desired motor current from desired operating parameters of the electric machine (torque, speed, direction of rotation). Continue For example, switching times of the power switch of the converter can be calculated from the desired terminal differential voltages.

A unit for determining at least one mean phase voltage determines at least one mean phase voltage of the converter at least as a function of a desired energy transfer into the low-voltage range or out of the low-voltage range. Here, the mean phase voltage is a voltage to be set by the voltage conversion element. The mean phase voltage is therefore the phase voltage of the half-bridge or half-bridges which also include the power switches of the voltage conversion element.

The half bridge is placed between a high voltage supply path and a low voltage supply path, e.g. In this context, the phase voltage of a half-bridge designates the drop across the power switch of the half-bridge, which is arranged between a section between the power switches of the half-bridge and the supply path with the low voltage.

Furthermore, at least one unit for determining at least one motor voltage of the electric machine determines a motor voltage of the electric machine at least as a function of a desired mechanical power of the electric machine. Motor voltage is understood to be a voltage whose properties (e.g. amplitude, frequency, phase) determine a speed and/or a torque and/or a direction of rotation of the electric machine. If the electric machine is connected in a star connection, for example, the motor voltages refer to the phase voltages of the electric machine. If the electric machine is not connected in a star connection, the motor voltages can be calculated using the methods explained later. The terminal differential voltages of the electric machine can also be derived from the motor voltages, which can also determine an operating mode (torque, speed, direction of rotation) of the electric machine. At least one unit for determining at least one setpoint phase voltage determines a setpoint phase voltage of at least one half bridge of the converter at least as a function of the mean phase voltage and the motor voltage. In particular, a desired mode of operation (motor or generator operation with a desired speed and a desired torque) can be set by means of the at least one motor voltage or its properties. The average phase voltage determines, among other things, whether energy is transferred from the electric machine to the low-voltage area or from the low-voltage area to the electric machine. Since the circuit breakers of the element for voltage conversion are at the same time circuit breakers of the converter, problems can arise here if a mean phase voltage deviates from a phase voltage determined from a desired motor voltage.

In order to avoid these problems, the unit for determining at least one target phase voltage determines the final target phase voltage of the converter to be set, in particular also the phase voltage of the at least one half bridge, which at the same time includes power switches of the element for voltage conversion and the converter, depending on the determined mean phase voltage and the at least one motor voltage. This results in different methods for determining the at least one setpoint phase voltage.

If, for example, the electrical machine is a three-phase electrical machine and the converter is a three-phase converter and only includes a first half-bridge, which is assigned to a first phase of the electrical machine, circuit breakers that are also circuit breakers of the element for voltage conversion, the unit for determining at least one setpoint phase voltage in a first operating mode, set the target phase voltage of the first half-bridge equal to the mean phase voltage determined by the at least one unit for determining a mean phase voltage. At the same time, the unit for determining at least one target phase voltage can calculate the target phase voltage of the second half bridge as a sum of the mean phase voltage of the first half bridge (target phase voltage of the first half bridge) and a desired terminal difference voltage between the to the first half bridge determine the terminal of the electric machine connected to the converter and the terminal of the electric machine connected to the second half-bridge. Similarly, the third phase voltage can be determined as a sum of the target phase voltage of the first half-bridge and a desired terminal differential voltage between the first terminal of the electric machine and the third terminal of the electric machine.

In a second mode of operation, the first target phase voltage is calculated as a sum of the average phase voltage and a desired first motor voltage. Similarly, a second target phase voltage is the sum of the mean phase voltage and a desired second motor voltage calculated. Similarly, a target third phase voltage is calculated as a sum of the average phase voltage and a desired third motor voltage.

The unit for determining at least one average phase voltage, the unit for determining at least one motor voltage and the unit for determining at least one target phase voltage can be integrated into the control unit or designed as separate control units. Furthermore, the control unit or a sub-unit of the control unit controls switching of the power switches of the converter as a function of the setpoint phase voltage determined. This advantageously results in converter operation with desired properties (direction of energy transmission, amount of energy transmitted) and desired operation of the electric machine (motor or generator operation) with desired properties (e.g. torque, speed, direction of rotation) by means of the converter becomes.

In a further advantageous manner, the device according to the invention makes it possible for a charging or discharging current of the vehicle electrical system battery not to flow additionally via the inductances, for example windings of the electric machine, which can lead to a lower maximum torque or to torque fluctuations, for example.

In an advantageous embodiment of the invention, when the electric machine is operating as a motor, the electric machine can be supplied with energy exclusively from the vehicle electrical system battery. This advantageously results in the electric machine being able to be supplied with energy solely from the vehicle electrical system battery. As a result, no further energy stores need to be arranged in the motor vehicle to supply energy to the electric machine.

In a further embodiment, the converter is designed as a three-phase converter, with each phase of the converter being assigned a half-bridge, each with two circuit breakers. Analogous to the previous statements, a section between the power switches of each half-bridge is electrically connected to terminals of a three-phase electrical machine via first supply paths. The element for voltage conversion includes six power switches and three inductances, the six power switches being the two power switches of the half-bridges of the converter. The inductances of the voltage conversion element are each arranged in second supply paths, the second supply paths electrically connecting the low-voltage range and the section of the respective half-bridge lying between the power switches of the respective half-bridge and being different from the first supply paths. The design of the element for voltage conversion with six power switches and three inductors advantageously increases the degree of freedom of control in converter operation of the element for voltage conversion. A converter function of the element for voltage conversion is performed here by means of the power switches of all half-bridges, which advantageously enables symmetrical control of the electric machine even while a conversion function of the element for voltage conversion is being exercised. The three inductances of the element for voltage conversion are preferably designed to be the same. Compared to the embodiment with only one inductance, however, the respective inductances of the element for voltage conversion can be designed for smaller currents.

In a further embodiment, the control unit can be used to control switching of the power switches of the converter and thus also of the element for voltage conversion as a function of at least one desired mechanical output of the electric machine and a desired energy transfer into the low-voltage range or out of the low-voltage system. A desired mechanical power of the electric machine includes a mechanical power in motor operation, eg depending on a desired speed and a desired torque, and a desired mechanical power in generator operation, eg depending on a desired braking torque of the electric machine. Here, the control unit essentially has to fulfill two tasks. On the one hand, at least two circuit breakers of the converter, which are also circuit breakers of the element for voltage conversion, must be controlled in such a way that a desired energy transfer from the low-voltage range to the electric machine or from the electric machine into the low-voltage range is made possible. Furthermore, the control unit must control all power switches of the converter, ie also the power switches of the element for voltage conversion, in such a way that a desired mechanical output of the electric machine is set. Various control methods are explained in more detail below. The device according to the invention results in an advantageous manner that a desired energy transmission with the desired transmission direction and desired Amount of energy can be adjusted simultaneously to a desired mode of operation of the electric machine by means of the control unit.

In a further embodiment, the vehicle electrical system has at least one high-voltage area with a second voltage level, the second voltage level being higher than the first voltage level. The high-voltage area is preferably connected to the intermediate circuit capacitor via a supply path. An (output) voltage of the vehicle electrical system battery, that is to say a DC voltage with the first voltage level, can be converted to a voltage with the second voltage level by means of the element for voltage conversion. In this way, it is possible in an advantageous manner to also connect electrical loads to the vehicle electrical system that are designed for an operating voltage that is higher than an output voltage of the vehicle electrical system battery. The element for voltage conversion advantageously makes it possible for electrical energy to be transmitted from the low-voltage range to the high-voltage range and/or to the electric machine. At the same time, when the electric machine is operating as a generator, electrical energy can be transferred from the electric machine into the high-voltage range and/or into the low-voltage range.

A method for energy transmission in a motor vehicle is also proposed, the motor vehicle having a device for energy transmission in accordance with the explanations above. When the electric machine is operating as a generator, a control unit controls circuit breakers of the element for voltage conversion, which are also circuit breakers of a converter, in such a way that electrical energy generated by the electric machine is at least partially transferred into the low-voltage range, in particular to the on-board battery. In this case, a control unit determines switching times of the circuit breakers and controls switching of these circuit breakers according to the calculated switching times. Furthermore, the control unit controls the power switches of the element for voltage conversion in motor operation in such a way that energy from the low-voltage range, in particular electrical energy stored in the vehicle electrical system battery, is at least partially transmitted to the electric machine. When the electric machine is operating as a motor, the electric machine can be supplied with energy partially or exclusively from the vehicle electrical system battery. The method according to the invention advantageously enables an electric machine to be used simultaneously as a motor, e.g. as a starter, or as a generator, e.g. as an alternator, in which case the electric machine can be supplied with energy, e.g. Furthermore, the electrical energy generated in generator operation can also be stored in the vehicle electrical system battery and/or used to supply energy to electrical consumers assigned to the low-voltage range. The method for controlling the circuit breakers, which is carried out by means of the control unit, makes it possible for two different functions of the converter to be carried out simultaneously. A first function here is a converter function, the switching times of power switches of the element for voltage conversion being controlled as a function of a desired energy transfer into the low-voltage range or out of the low-voltage range. In a second function, the method for controlling the circuit breakers enables the electric machine to be operated with desired operating parameters such as e.g. B. a desired torque and / or a desired speed.

A control or regulation of the circuit breakers can also take place via a so-called control or regulation hierarchy with several levels. In this case, for example, a desired current strength and/or current direction can be specified by the at least one inductor of the element for voltage conversion. The control unit or sub-units of the control unit determine an intermediate circuit voltage to be set by means of the voltage conversion element from the desired current intensity and/or current direction. From this, in turn, switching times of the power switches of the element for voltage conversion can be calculated. Likewise, the control unit or a sub-unit of the control unit can determine a desired terminal differential voltage and/or a desired motor current from desired operating parameters of the electric machine (torque, speed, direction of rotation). Furthermore, switching times of the circuit breakers of the converter can be calculated from the desired terminal differential voltages, for example.

A unit for determining at least one mean phase voltage determines at least one mean phase voltage of the converter at least as a function of a desired energy transfer into the low-voltage range or out of the low-voltage range. Here, the mean phase voltage is a voltage to be set by the voltage conversion element. The mean phase voltage is therefore the phase voltage of the half-bridge or half-bridges which also include the power switches of the voltage conversion element.

The half bridge is arranged between a high voltage supply path and a low voltage supply path, eg ground. In this context, the phase voltage of a half-bridge designates the drop across the power switch of the half-bridge, which is arranged between a section between the power switches of the half-bridge and the supply path with the low voltage.

Furthermore, at least one unit for determining at least one motor voltage of the electric machine determines a motor voltage of the electric machine at least as a function of a desired mechanical power of the electric machine. Motor voltage is understood to be a voltage whose properties (e.g. amplitude, frequency, phase) determine a speed and/or a torque and/or a direction of rotation of the electric machine. If the electric machine is connected in a star connection, for example, the motor voltages refer to the phase voltages of the electric machine. If the electric machine is not connected in a star connection, the motor voltages can be calculated using the methods explained later. The terminal differential voltages of the electric machine can also be derived from the motor voltages, which can also determine an operating mode (torque, speed, direction of rotation) of the electric machine. At least one unit for determining at least one setpoint phase voltage determines a setpoint phase voltage of at least one half bridge of the converter at least as a function of the mean phase voltage and the motor voltage. In particular, a desired mode of operation (motor or generator operation with a desired speed and a desired torque) can be set by means of the at least one motor voltage or its properties. The average phase voltage determines, among other things, whether energy is transferred from the electric machine to the low-voltage area or from the low-voltage area to the electric machine. Since the circuit breakers of the element for voltage conversion are at the same time circuit breakers of the converter, problems can arise here if a mean phase voltage deviates from a phase voltage determined from a desired motor voltage.

In order to avoid these problems, the unit for determining at least one target phase voltage determines the final target phase voltage of the converter to be set, in particular also the phase voltage of the at least one half bridge, which at the same time includes power switches of the element for voltage conversion and the converter, depending on the determined mean phase voltage and the at least one motor voltage. This results in different methods for determining the at least one target phase voltage.

If, for example, the electrical machine is a three-phase electrical machine and the converter is a three-phase converter and only includes a first half-bridge, which is assigned to a first phase of the electrical machine, circuit breakers that are also circuit breakers of the element for voltage conversion, the unit for determining at least one setpoint phase voltage in a first operating mode, set the target phase voltage of the first half-bridge equal to the mean phase voltage determined by the at least one unit for determining a mean phase voltage. At the same time, the unit for determining at least one target phase voltage can calculate the target phase voltage of the second half bridge as a sum of the mean phase voltage of the first half bridge (target phase voltage of the first half bridge) and a desired terminal difference voltage between the to the first half bridge determine the terminal of the electric machine connected to the converter and the terminal of the electric machine connected to the second half-bridge. Similarly, the third phase voltage can be determined as a sum of the target phase voltage of the first half-bridge and a desired terminal differential voltage between the first terminal of the electric machine and the third terminal of the electric machine.

In a second mode of operation, the first target phase voltage is calculated as a sum of the average phase voltage and a desired first motor voltage. Similarly, a second target phase voltage is calculated as the sum of the mean phase voltage and a desired second motor voltage. Similarly, a target third phase voltage is calculated as a sum of the average phase voltage and a desired third motor voltage.

The unit for determining at least one average phase voltage, the unit for determining at least one motor voltage and the unit for determining at least one target phase voltage can be integrated into the control unit or designed as separate control units. Furthermore, the control unit or a sub-unit of the control unit controls switching of the power switches of the converter as a function of the setpoint phase voltage determined. This advantageously results in converter operation with desired properties (direction of energy transmission, amount of energy transmitted) and desired operation of the electric machine (motor or generator). cal operation) with desired properties (e.g. torque, speed, direction of rotation) is made possible by means of the converter.

In one embodiment, a desired energy transfer into or out of the low-voltage range and a desired mechanical power of the electric machine are determined by a strategy unit at least as a function of an intermediate circuit voltage and/or at least one sensor signal relating to driving dynamics and/or at least one sensor signal specific to driving operation. This results in an advantageous manner in that a permissible upper limit of an intermediate circuit voltage, which is specified, for example, by operating parameters of the intermediate circuit capacitor, is not exceeded. In this way, in particular, a destruction of the intermediate circuit capacitor is avoided. The strategy unit here forms a top control or regulation level of a control or regulation hierarchy. Here, in particular, the desired energy transfer, now to be regarded as manipulated variables, into or out of the low-voltage range and the desired mode of operation of the electric machine are adapted to an intermediate circuit voltage. In addition or as an alternative, variables relating to driving dynamics, for example a speed or an acceleration of the vehicle, can also be taken into account. In addition or as an alternative, input variables such as the position of the accelerator pedal, brake pedal and/or selector lever can also be taken into account when determining the two manipulated variables. In this case, sensor signals specific to driving operation designate output signals, e.g. from an accelerator pedal sensor, a brake pedal sensor and/or a selector lever position sensor.

In a further specific embodiment, the unit for determining at least one setpoint phase voltage determines the at least one setpoint phase voltage as a function of a speed of the electric machine. In particular, the switching of the power switches of the converter can be controlled according to the first operating mode explained above and the second operating mode explained above as a function of a rotational speed. Ideally, the unit for determining at least one setpoint phase voltage determines the at least one setpoint phase voltage in such a way that, particularly in the first operating mode, a differential terminal voltage does not exceed the average phase voltage determined by the unit for determining an average phase voltage. Ideally, the unit for determining at least one target phase voltage determines the at least one target phase voltage in the second operating mode in such a way that an AC component of the current through the at least one inductance of the element for voltage conversion remains sufficiently small, for example is smaller than a predetermined threshold value.

For reasons of simpler implementation, however, a speed-dependent criterion for determining the at least one setpoint phase voltage can also be used instead of these criteria. For this purpose, the device according to the invention can advantageously include a sensor for detecting the speed of the electric machine. In the first operating mode, the current through the at least one inductance of the voltage conversion element is a direct current. However, in the first operating mode, the level of a differential terminal voltage is limited to half the intermediate circuit voltage in the most favorable case, as a result of which it is not possible to operate the electric machine with a differential terminal voltage above the limit. In the second operating mode, a differential terminal voltage can assume the level of the intermediate circuit voltage. However, in this case, an alternating current component is superimposed on a direct current flowing through the at least one inductance of the at least one element for voltage conversion. The advantages of each operating mode can be exploited in an advantageous manner as a result of the speed-dependent switchover between the two operating modes.

In a further embodiment, the unit for determining at least one target phase voltage determines the at least one target phase voltage according to a first and a second operating mode, with switching between the first and second operating modes depending on the speed of the electric machine, with switching being a hard switching, or hysteresis-based switching, or fade-based switching. In the simplest case (hard switching), a “hard” switch is made between the first operating mode and the second operating mode at a predetermined speed limit. This switching is easy to implement in an advantageous manner. However, if the electric machine fluctuates around the predetermined speed limit in a small speed interval for a longer period of time, it could happen that a target phase voltage, for example of the first phase, deviates from an average phase voltage determined for the first phase at unfavorably selected switchover times. This can advantageously be avoided by means of hysteresis-based switching. To this end, two predetermined speed limits are set, an upper speed limit and a lower speed limit. If the speed of the electric machine exceeds the upper limit, the target phase voltages are determined according to the second operating mode. If the speed falls below the If the electric machine is now the lower limit, the target phase voltages are determined according to the first operating mode. Between the lower and upper limit or between the upper and lower limit (hysteresis range), the operating mode to which you last switched is retained. In unfavorable cases, “hard” switching can produce unpleasant acoustic noises. This can be avoided in an advantageous manner by a fade-based switching. In this case, target phase voltages are again determined above an upper limit according to the second operating mode. Below a lower speed limit, target phase voltages are determined according to the first operating mode. In the range between the lower and the upper speed limit, the setpoint phase voltages are interpolated, for example, linearly between the setpoint phase voltages determined according to the first and the second operating mode. A fade factor can be used for this purpose, for example.

Furthermore, the device according to the invention can have at least one sensor for sensing a rotor position of the electric machine and/or a sensor for sensing a phase current of the electric machine and/or a sensor for sensing the first voltage level and/or a sensor for sensing the second voltage level and/or a sensor for sensing a charging or discharging current of the vehicle electrical system battery and/or a sensor for sensing a current flowing through the at least one inductance of the element for voltage conversion, the control unit switching the power switches of the converter as a function of at least the rotor position and/or the phase current and/or the first voltage level and/or the second voltage level and/or the charging and/or discharging current and/or the current flowing through the at least one inductor. The various sensor signals can be evaluated at different levels of the control hierarchy.

A thin-film capacitor (supercap, boostcap) can also be connected in parallel with the intermediate circuit capacitor. This can advantageously take up or deliver similar or even greater power than the on-board battery in a matter of seconds. In this case, a power consumption or output can also advantageously take place simultaneously with a power consumption or output of the vehicle electrical system battery. As a result, the electric machine can also be operated at higher powers, at least for a short time, than when it is operated exclusively via the vehicle electrical system battery.

Furthermore, the control unit can switch the circuit breakers depending on energy transfer into a high-voltage range of the vehicle electrical system or out of the high-voltage range of the vehicle electrical system and/or depending on losses, e.g. ohmic losses and/or hysteresis losses in the electric machine and/or switching losses in the circuit breakers. The energy to be transmitted into the high-voltage range and/or the losses can be viewed here as disturbance variables from the point of view of control technology. Their respective size is determined outside of the open-loop or closed-loop control and cannot be determined by the control unit independently of the energy to be transmitted into the low-voltage range and the energy generated by the electric machine. As is known in control engineering, it can be useful to precontrol these disturbance variables to improve the control quality. For this purpose, for example, the main energy consumers who are responsible for the energy to be transmitted in the high-voltage range can report a measured or estimated value of their currently consumed power to the control unit. This can be done, for example, via a data bus, for example a CAN bus. The losses can be estimated, for example, by the control unit calculating or estimating a simple loss model. If a pilot control is carried out by means of the control unit, the control unit then ideally only needs to compensate for a deviation between estimated and real disturbance variables during operation. This advantageously results in the fact that total amounts of the disturbance variables do not have to be compensated for.

• 1 ein schematischer Schaltplan einer Vorrichtung zur Energieübertragung (Stand der Technik),
• 2 ein schematischer Schaltplan einer erfindungsgemäßen Vorrichtung zur Energieübertragung,
• 3 ein schematischer Schaltplan einer weiteren erfindungsgemäßen Vorrichtung zur Energieübertragung und
• 4 ein schematisches Blockschaltbild eines Verfahrens zur Energieübertragung.

The invention is explained in more detail using second exemplary embodiments. The figures show:

• 1 a schematic circuit diagram of a device for energy transmission (prior art),
• 2 a schematic circuit diagram of a device according to the invention for energy transmission,
• 3 a schematic circuit diagram of a further device according to the invention for energy transmission and
• 4 a schematic block diagram of a method for energy transmission.

In the following, the same reference symbols designate elements with the same or similar technical properties.

1 shows a schematic circuit diagram of a device 1 for energy transmission in a motor vehicle according to the prior art. The device 1 includes an on-board electrical system (not shown in full) with a low-voltage area 2 and a high-voltage area 3. In this case, the low-voltage area 2 has a first voltage level of 12 V, which corresponds to a battery voltage U _batt =12 V. The high-voltage area 3 shown schematically has a second voltage level of 42V. In this case, the low-voltage area 2 includes an on-board power supply battery 4 which has an output voltage Ubatt of 12V. Further, schematically illustrated electrical consumers 5 are connected to the low-voltage area 2 . The device 1 also includes an electric machine 6. The electric machine 6 is shown as a three-phase electric machine 6. FIG. In this case, the electric machine 6 has three terminals K1 , K2 , K3 of the electric machine 6 . It is also shown that the strands of the electric machine 6 represented by the motor inductances ML1, ML2, ML3 are connected in a star circuit to the star point S. The respective motor voltages U _S1 , U _S2 , U _S3 drop across the motor inductances ML1, ML2, ML3. in the in 1 The illustrated embodiment, the motor voltages U _S1 , U _S2 , U _S3 are equal to the phase voltages of the electric machine 6. The device 1 also includes a three-phase converter 7. The three-phase converter 7 includes three half-bridges. A first half-bridge includes a first switch S1 and a second switch S2 of the first half-bridge, with diodes D1, D2 being connected antiparallel to the switches. A second half-bridge of the converter 7 includes a first switch S3 and a second switch S4 of the second half-bridge. Analogously, diodes D3, D4 are connected anti-parallel to the first switch S3 and second switch S4 of the second half-bridge. A third half-bridge includes a first switch S5 and a second switch S6 of the third half-bridge, with diodes D5, D6 in turn being connected antiparallel to the first and second switches S5, S6 of the third half-bridge. Phase voltages U _{P1 ,} U _P2 , U _P3 are set using the power switches S1, S2, S3, S4, S5, S6. The difference between a first phase voltage U _P1 and a second phase voltage U _P2 forms a differential terminal voltage U _K1-K2 between the first terminal K1 and the second terminal K2 of the electric machine 6. A second differential terminal voltage U _K1 is analogous _-K3 and a third differential terminal voltage U _K2-K3 determined. By switching the power switches S1, S2, S3, S4, S5, S6, predetermined phase voltages and thus predetermined differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 can be set. An intermediate circuit capacitor C _ZK is connected in parallel with the half-bridges. An intermediate circuit voltage U _ZK drops across the intermediate circuit capacitor C _ZK . An element 8 for voltage conversion is connected between the low-voltage area 2 and the intermediate circuit capacitor C _ZK . The element 8 for voltage conversion includes an inductor L and two power switches S7, S8, with diodes D7, D8 in turn being connected antiparallel to the power switches. The element 8 for voltage conversion is a so-called DC/DC converter.

Operation of the power transmission device 1 is outlined below. Initially, all circuit breakers S1, ..., S8 are open. The intermediate circuit capacitor C _ZK is then charged via the inductance L and the diode D7 antiparallel to the power switch S7 of the element 8 for voltage conversion to approximately the battery voltage Ubatt. If, for example, a higher intermediate circuit voltage U _ZK is required to start an internal combustion engine, for which the electric machine 6 acts as a starter, the circuit breaker S8 can be closed. A current iL then builds up through the inductance L against the in 1 shown current direction of iL. If the circuit breaker S8 is opened again, the inductance L continues to drive the current iL, which flows through the diode D7, which is connected antiparallel to the circuit breaker S7, into the intermediate circuit capacitor C _ZK and thus increases the intermediate circuit voltage U _ZK . In order to reduce losses, the circuit breaker S7 can also be closed in this phase. The magnitude of the current iL through the inductance L decreases. In this case, element 8 is used for voltage conversion as a step-up converter from battery voltage Ubatt to intermediate circuit voltage U _ZK .

When the internal combustion engine is running, for example, the electric machine 6 can also work as a generator, for example as an alternator. In this case, the three-phase converter 7 is controlled in such a way that the intermediate circuit voltage U _ZK is greater than the battery voltage Ubatt. The element 8 for voltage conversion is now used as a step-down converter from the intermediate circuit voltage U _ZK to the battery voltage Ubatt in order to supply electrical consumers 5 and/or to charge the vehicle electrical system battery 4 . Here, the power switch S7 is closed. A current iL then builds up in the in 1 shown current direction of iL. If the power switch S7 is opened again, the inductance L continues to drive the current iL through the diode D8 without energy being drawn from the intermediate circuit. In order to reduce losses, the circuit breaker S8 can also be closed in this phase. The magnitude of the current iL through the inductance L decreases.

2 shows a schematic circuit diagram of a device 1 according to the invention for energy transmission. Analogous to the in 1 Device 1 shown comprises the device according to the invention 1 a low-voltage area 2 with an on-board battery 4 and electrical loads 5. The device 1 also includes a three-phase electric machine 6 and a three-phase converter 7. In 2 no anti-parallel diodes D1, . . . , D8 are shown here, which is only used to simplify the illustration. In 2 shows that a section between the power switches S1, S2 of the first half-bridge is connected to a first terminal K1 of the electric machine 6 via a first supply path. A first phase current i _P1 flows in the first supply path. Similarly, sections between the power switches S3, S4 and S5, S6 of the second and third half-bridges are connected to the second and third terminals K2, K3 of the electric machine 6 via first supply paths, in which phase currents i _P2 , i _P3 flow. In 2 It is shown that the section between the power switches S1, S2 is additionally connected to the low-voltage area 2, in particular to the on-board battery 4, via a second supply path. The inductance L of the element for voltage conversion is arranged in the second supply path. In this case, the element for voltage conversion is partially integrated into the converter 7 . It is shown that the power switches S1, S2 of the first half-bridge are used on the one hand as power switches S1, S2 of the converter 7 and on the other hand as power switches S1, S2 of the element for voltage conversion, which in 1 are shown as circuit breakers S7, S8.

It should be noted here that the power switches S1-S6 are preferably in the form of MOSFETs which, for technological reasons, automatically also generate the anti-parallel diodes D1-D6 as parasitic components.

In 3 a circuit diagram of a further device 1 according to the invention for energy transmission is shown. In this case, each section between the power switches S1, S2 and S3, S4 and S5, S6 of the half-bridges of the converter 7 is connected to the low-voltage area 2, in particular the on-board battery 4, via second supply paths. Inductances L1, L2, L3 are arranged in each case in the second supply paths. In this case, all circuit breakers S1, ..., S6 of the converter 7 function as circuit breakers of the converter and the element for voltage conversion.

ausgegangen. Hierbei bezeichnet P_EM z.B. eine von der in 2 dargestellten Elektromaschine 6 im motorischen Betrieb umgesetzte Leistung. Im motorischen Betrieb gibt die Elektromaschine 6 die mechanische Leistung P_Mech = M x Ω ab, wobei M ein Wellendrehmoment und Ω eine Winkelgeschwindigkeit eines Rotors der Elektromaschine 6 bezeichnet. Wird vereinfacht angenommen, dass die Elektromaschine 6 verlustlos ist, so ist die dem Bordnetz entnommene elektrische Leistung P_EM = P_Mech. Weiter bezeichnet die Leistung P_NV eine aus dem Niedrigspannungsbereich 2 heraus übertragene elektrische Leistung oder eine in den Niedrigspannungsbereich 2, d.h. zur Bordnetzbatterie 4 und zu den elektrischen Verbrauchern 5, übertragene Leistung. Die Leistung P_NV kann gemäß $${\text{P}}_{\text{NV}}={\text{U}}_{\text{batt}}\times {\text{i}}_{\text{L}}$$

berechnet werden. Die Leistung P_HV bezeichnet die von einem Hochspannungsbereich 3 aufgenommene oder abgegebene Leistung und berechnet sich gemäß $${\text{P}}_{\text{HV}}={\text{U}}_{\text{ZK}}\times {\text{i}}_{\text{HV}}$$

4 shows a schematic block diagram of a method for energy transmission. Essential aspects of the method for energy transmission, in particular a control or regulation of switching, for example in 2 illustrated circuit breakers S1, ..., S6 explained. Here is from a current account $$0={\text{P}}_{\text{EM}}+{\text{P}}_{\text{NV}}+{\text{P}}_{\text{HV}}+{\text{P}}_{\text{CC}}+{\text{P}}_{\text{exit}}$$

went out. Here, P _EM designates, for example, one of the in 2 Electric machine 6 shown in motor operation converted power. In motor operation, the electric machine 6 delivers the mechanical power P _Mech =M x Ω, where M denotes a shaft torque and Ω denotes an angular velocity of a rotor of the electric machine 6 . If, in simplified terms, it is assumed that the electric machine 6 has no losses, then the electrical power P EM taken from the vehicle electrical system is P _EM =P _Mech . Furthermore, the power P _NV designates an electrical power transmitted out of the low-voltage area 2 or an electrical power transmitted into the low-voltage area 2, ie to the vehicle electrical system battery 4 and to the electrical consumers 5. The power P _NV can according to $${\text{P}}_{\text{NV}}={\text{u}}_{\text{batt}}\times {\text{i}}_{\text{L}}$$

be calculated. The power P _HV designates the power absorbed or emitted by a high-voltage area 3 and is calculated according to $${\text{P}}_{\text{HV}}={\text{u}}_{\text{CC}}\times {\text{i}}_{\text{HV}}$$

auf.The intermediate circuit capacitor C _ZK absorbs the power during motor operation $${\text{P}}_{\text{CC}}={\text{u}}_{\text{CC}}\times {\text{i}}_{\text{CC}}$$

on.

In this context, P _Loss designates all losses, for example ohmic losses and hysteresis losses in the electric machine 6 and switching losses in the circuit breakers S1, . . . , S6.

In the method according to the invention, the power P _NV and the power P _EM can be set by switching the power switches S1, . . . , S6.

Motor operation of the electric machine 6 is assumed below. In a top level of the control hierarchy, a power P _NV to be drawn from the low-voltage range, in particular the vehicle electrical system battery 4, and an electrical power P _EM of the electric machine 6 are specified.

In this case, the power P _NV transmitted out of the low-voltage region 2 can be controlled by changing a current strength of the current iL flowing through the inductance L of the element for voltage conversion. Assuming no loss $${\text{u}}_{\text{L}}=\text{L}\times {\text{you}}_{\text{L}}/\text{German}$$

In this case, U _L designates a voltage drop across the inductance L. So if a first phase voltage U _P1 of a first half-bridge of the in 2 If the converter 7 shown is greater than the battery voltage Ubatt, then the current intensity of i _L increases. The current intensity of iL falls when the first phase voltage U _P1 is less than the battery voltage Ubatt. It is assumed here that the battery voltage Ubatt is constant and is 12 V. The current level and a current direction of the current iL can therefore be changed by adjusting the first phase voltage U _P1 . In this case, the current intensity and the current direction of the current iL can preferably be detected by means of a sensor, with the first phase voltage U _P1 being controlled using a difference between a setpoint current and a currently detected actual current i _L, setpoint −i _L .

In 4 It is shown that a unit 10 for determining a mean first phase voltage U _{P1M calculates} a mean first phase voltage U _P1M as a function of a target current i _L,soll and a detected current iL through the inductance L. It is shown here that the setpoint current i _{L,setpoint is} determined by a strategy unit 11 . The function of the strategy unit 11 will be explained in more detail later.

A major limitation of the 2 device 1 for energy transmission shown is that a mean value over time of the first phase voltage U _P1 must be equal to a mean value of the battery voltage Ubatt, since otherwise the vehicle electrical system battery would be permanently charged or discharged. In addition, the operating conditions of conventional rotating electrical machines 6 mean that mean values of the phase voltages U _{P1 ,} U _P2 , U _P3 must be the same. Under these assumptions, the unit 10 for determining the first mean phase voltage U _{P1M must} determine the first phase voltage U _P1 and also the other phase voltages U _P2 , U _P3 , at least on average over time, equal to the battery voltage Ubatt, regardless of the intermediate circuit voltage U _ZK . The intermediate circuit voltage U _ZK is preferably regulated to twice the battery voltage Ubatt. In this exemplary embodiment, therefore, U _ZK preferably corresponds to 24 V. A mean value of the phase voltage U _{P1 ,} U _P2 , U _P3 can then be set to half the intermediate circuit voltage U _ZK .

As is known, a phase voltage U _{P1 ,} U _P2 , U _P3 can be set by pulse width modulation. For example, the first phase voltage U _P1 can be set by the power switches S1, S2 of the first half-bridge being alternately closed or opened. Opening or closing can take place with a constant frequency. If, for example, a switch-on time T _S1 of the first power switch S1 of the first half bridge is equal to the switch-on time T _S2 of the second power switch S2 of the first half bridge within a period, the first phase voltage U _P1 is on average half the intermediate circuit voltage U _ZK/2 . If the first power switch S1 is permanently closed, the first phase voltage U _P1 is equal to the intermediate circuit voltage U _ZK . If the second power switch S2 is permanently closed, the first phase voltage U _P1 is equal to zero. The mean value of the first phase voltage U _P1 can be set anywhere between zero and the intermediate circuit voltage U _ZK by a ratio of the switch-on times T _S1 , T _S2 to the period duration (sum of the switch-on times T _S1 + T _S2 ): $${\text{<figure-callout id="1" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}/{\text{u}}_{\text{CC}}={\text{<figure-callout id="1" label="T S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">T</figure-callout>}}_{\text{S}}/\left({\text{<figure-callout id="1" label="T S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">T</figure-callout>}}_{\text{S}}+{\text{T}}_{\text{S}2}\right)$$

As previously mentioned, the electrical power P _EM to be generated by the electric machine 6 can also be adjusted. Known methods for controlling electrical machines can essentially also be used for the in 2 device shown are applied. In this case, it can generally be assumed that a setpoint torque M setpoint _is specified by a top level of a controller hierarchy _, with the setpoint torque M setpoint being determined with the aid of known methods and using other input variables from a unit 12 for determining motor voltages U _S1 , U _S2 , U _S3 to be determined. In 2 an electric machine 6 is shown, which is connected according to a so-called star connection. In this case, a first motor voltage U _S1 corresponds to a phase voltage present between a first terminal K1 and a star point S of the electric machine 6 . Analogously, a second motor voltage U _S2 designates a phase voltage dropping between a second terminal K2 of the electric machine 6 and the star point S. Analogously, a third motor voltage U _S3 designates a phase voltage dropping between a third terminal K3 and a star point S of the electric machine 6 . It should be noted here that the in 2 motor voltages U _S1 , U _S2 , U _S3 shown cannot be shown directly for each connection of an electric machine 6 . If the electric machine 6 is connected in a delta circuit, for example, then the motor voltages U _S1 , U _S2 , U _S3 mentioned here cannot be measured directly, but can only be calculated indirectly. Methods for calculating the motor voltages U _S1 , U _S2 , U _S3 for any configuration of electric machines will be explained in more detail later. Differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2 - _K3 can be determined by means of the motor voltages U _S1 , U _S2 , U _S3 . A first differential terminal voltage U _K1-K2 describes a voltage difference between a voltage present at the first terminal K1 and a voltage present at the second terminal K2. A second differential terminal voltage U _K1-K3 and a third differential terminal voltage U _K2-K3 are defined analogously. The differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 correspond to a difference in the phase voltages U _P1 - U _P2 , U _P1 - U _P3 , U _P2 - U _P3 . This makes it clear that desired motor voltages U _S1 , U _S2 , U _S3 can be set by adjusting the phase voltages U _P1 , U _P2 , U _P3 .

As a rule, to determine the motor voltages U _S1 , U _S2 , U _S3 from the target torque M target _, target phase currents i _P1, target , i _P2, target , i _P3, target are calculated using a rotor position of the electric machine 6 detected by a motor position sensor . The motor voltages U _S1 , U _S2 , U _S3 are calculated from this, possibly using phase currents i _P1 , i _P2 , i _P3 detected by means of sensors.

Often, but not necessarily, the motor voltages U _S1 , U _S2 , U _S3 are cosine, e.g $${\text{u}}_{\text{S}}$$$$1_{}={\text{u}}_{\text{A}}\times \text{cos}\left(\mathrm{a}\right);{\text{<figure-callout id="2" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}={\text{u}}_{\text{A}}\times \text{cos}\left(\mathrm{a}+120°\right);{\text{<figure-callout id="3" label="u S" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}={\text{u}}_{\text{A}}\times \text{cos}\left(\mathrm{a}+240°\right)$$

Here, U _A designates a maximum voltage amplitude of the motor voltage U _S1 , U _S2 , U _S3 and α a rotor position of the rotor of the electric machine 6 (not shown). 6. It is important for the method according to the invention that a time average of the motor voltage U _S1 , U _S2 , U _S3 is approximately zero when the electric machine 6 is rotating.

A unit 13 for determining setpoint phase voltages U _{P1,soll ,} U _{P2,soll , U P3,soll} determines setpoint values for the phase voltages U _P1,soll , U _P2,set, U _P3,set . The setpoint phase voltages _UP1, set, UP2,set _{, UP3,} set are determined in two different operating modes.

A first operating mode is used for a standstill (speed of the electric machine 6 equal to zero) and low speeds of the electric machine 6 . In this case, the first target phase voltage U _{P1,setpoint is} set equal to the first mean phase voltage U _P1M determined by the unit 10 for determining the first mean phase voltage U _P1M . The remaining setpoint phase voltages are determined in such a way that the terminals K1, K2, K3 of the electric machine 6 have differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 which are caused by the motor voltage U _S1 , U _S2 , U _S3 are specified. The desired phase voltages U _P1,soll , U _{P2,soll ,} U _P3,soll are determined here according to $${\text{<figure-callout id="1" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}};{\text{<figure-callout id="2" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+\left({\text{<figure-callout id="2" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}-{\text{u}}_{\text{S}1}\right);{\text{<figure-callout id="3" label="u P" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+\left({\text{<figure-callout id="3" label="u S" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}-{\text{u}}_{\text{S}1}\right)$$

The first operating mode is characterized in that the first phase voltage U _P1 and the motor voltages U _S1 , U _S2 , U _S3 can be set independently of one another even when the electric machine 6 is stationary and delivering a high torque. It is thus possible to transfer a desired power P _NV out of the low-voltage area 2 . At the same time it is possible to operate the electric machine 6 in a desired mode of operation, ie with a desired torque and a desired speed.

The disadvantage here is that a terminal differential voltage U _K1-K2 , U _K1-K3 , U _K2-K3 at the terminals K1 , K2 , K3 of the electric machine 6 may not exceed the mean phase voltage U _P1M . This can be derived as shown below. According to a mesh equation: $${\text{<figure-callout id="2" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{<figure-callout id="1" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}+{\text{u}}_{\text{S}2}-{\text{<figure-callout id="1" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}$$

The phase voltages U _{P1 ,} U _P2 , U _P3 , in particular also the second phase voltage U _P2 , can be set anywhere between 0 and 24 V by means of the power switches S3, S4, as explained above. In the first operating mode, the first phase voltage U _P1 is constant and, as explained above, on average equal to the battery voltage Ubatt = 12 V. A difference between the second and the first motor voltage U _S2 - U _S1 (differential terminal voltage U _{K1 -K2} ) must only be between -12 V and 12 V. This has the disadvantage that in the first operating mode the electric machine 6 can also be operated exclusively with differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 with a maximum amplitude of -12V or 12V if the electric machine 6 is designed for higher amplitudes of the differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 .

The second operating mode is intended for higher speeds. Here, the setpoint phase voltages U _P1, set, U _P2,set, U _P3, set are determined according to $${\text{<figure-callout id="1" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+{\text{<figure-callout id="1" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}};{\text{<figure-callout id="2" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+{\text{<figure-callout id="2" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}};{\text{<figure-callout id="3" label="u P" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+{\text{<figure-callout id="3" label="u S" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}$$

Here, the motor voltages U _S1 to U _S3 are added to the average phase voltage U _P1M determined by the unit 10 in order to obtain the target phase voltages U _P1, set , U _{P2,set ,} U _P3, set. It should be noted here that in the second operating mode the requirement to regulate the first phase voltage U _P1 to a constant mean phase voltage U _P1M is not exactly implemented. In this case, the first motor voltage U _S1 determined by the unit 12 is superimposed on the first mean phase voltage U _P1M . The first motor voltage U _S1 (and also the further motor voltages U _S2 , U _S3 ) is preferably an AC voltage with a mean value of zero or close to zero. Depending on the size of the inductance L of the element for voltage conversion, an alternating current with the speed-dependent frequency of the first motor voltage U _S1 is thus superimposed on the current iL. In this case, however, it can be assumed that a mean value of the current iL essentially does not change due to the superimposition of an alternating current. A differential terminal voltage U _K1-K2 , U _K1-K3 , U _K2-K3 at the terminals K1, K2, K3 of the electric machine 6 can have an amplitude in the second operating mode that is theoretically twice the average determined by the unit 10 first phase voltage U corresponds to _P1M . If, for example, the battery voltage Ubatt = 12 V and the intermediate circuit voltage U _ZK = 24 V, the electric machine can also be operated with differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 with amplitudes of -24 V to 24 V are operated. This is explained in more detail below. Based on the mesh equation from formula 9, the first and the second phase voltage U _{P1 ,} U _P2 can be set in the range between 0 V and 24 V, since the first phase voltage U _P1 is no longer a constant phase voltage. It follows from this that the first differential terminal voltage U _K1-K2 , which corresponds to the difference between the second and the first motor voltage U _S2 -U _S1 , can theoretically assume voltage amplitudes between -24 V and 24 V.

1. 1. Im ersten Betriebsmodus sollten die Differenz-Klemmen-Spannungen U_K1-K2, U_K1-K3, U_K2-K3 an den Klemmen K1, K2, K3 die erste mittlere Phasenspannung U_P1M nicht überschreiten.
2. 2. Im zweiten Betriebsmodus sollte ein Wechselstromanteil des Stromes iL durch die Induktivität L des Elements zur Spannungswandlung ausreichend klein bleiben.

Ideally, switching between the first and the second operating mode should meet the following requirements:

1. 1. In the first operating mode, the differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 at terminals K1, K2, K3 should not exceed the first average phase voltage U _P1M .
2. 2. In the second operating mode, an AC component of the current iL through the inductance L of the element for voltage conversion should remain sufficiently small.

For reasons of simpler feasibility, these criteria are not used directly, but rather a criterion that is dependent on the rotational speed Ω of the electric machine 6 for switching between the first and the second operating mode. In this case, switching as a function of the speed Ω can be a hard switching, a hysteresis-based or a fade-based switching. A crossfade-based switching is now explained below. For a fade-based switching, an upper speed limit and a lower speed limit are predetermined. Above the upper speed limit, the setpoint phase voltages U _P1,soll , U _{P2,soll ,} U _P3,soll are determined according to the second operating mode and below the lower speed limit according to the first operating mode. Between the lower and the upper speed limit, linear interpolation takes place between the target phase voltages U _P1, target , U _{P2,target ,} U _P3, target determined according to the two operating modes. A fade factor u _fak is used for this. If the speed Ω is less than the lower speed limit, the fade factor u _fak = 0. If the speed Ω is greater than the upper speed limit, the fade factor u _fak = 1. If the speed Ω is between the lower and the upper speed limit, the fade factor u _fak is determined according to $$\left(\mathrm{\Omega }-\text{lower speed limit}\right)/\left(\text{upper speed limit}-\text{lower speed limit}\right)$$

The desired phase voltages U _P1,soll , U _{P2,soll ,} U _P3,soll are then determined according to $$\begin{array}{l}{\text{<figure-callout id="1" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+{\text{and}}_{\text{fac}}\times {\text{<figure-callout id="1" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}},\hfill \\ {\text{<figure-callout id="2" label="u P" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+{\text{<figure-callout id="2" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}-\left(1-{\text{and}}_{\text{fac}}\right)\times {\text{<figure-callout id="1" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}},\hfill \\ {\text{<figure-callout id="3" label="u P" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{P}}={\text{u}}_{\text{P}1\text{M}}+{\text{<figure-callout id="3" label="u S" filenames="DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}-\left(1-{\text{and}}_{\text{fac}}\right)\times {\text{<figure-callout id="1" label="u S" filenames="DE102010019151B4\_0017.png,DE102010019151B4\_0018.png" state="{{state}}">u</figure-callout>}}_{\text{S}}\hfill \end{array}$$

The switching times of the power _{switches S1 ,} U _ZK determined and the circuit breakers S1, ..., S6 controlled accordingly.

The power P _HV transmitted into the high-voltage area 3 and the power loss P _Verl can be regarded as interference variables from the point of view of control technology. These can be at least partially compensated for, for example, by means of a pilot control, as a result of which the control quality of the control of the power P _NV to be transmitted from the low-voltage range 2 and the electrical power P _EM of the electric machine 6 is improved.

und $${\text{dU}}_{\text{ZK}}/\text{dt}=1/{\text{C}}_{\text{ZK}}\times {\text{i}}_{\text{ZK}}$$

von der Leistung P_ZK ab. Überschreitet z.B. die Zwischenkreisspannung U_ZK eine zulässige obere Grenze der Zwischenkreisspannung U_ZK, so können der Zwischenkreiskondensator C_ZK und/oder Leistungsschalter S1, ..., S6 zerstört werden. Unterschreitet die Zwischenkreisspannung U_ZK z.B. einen Wert von 2 x Ubatt, so kann die Elektromaschine nur mit eingeschränkter Leistung betrieben werden und/oder es können Drehmomentschwankungen auftreten. Hieraus folgt, dass auch die Zwischenkreisspannung U_ZK vorzugsweise gesteuert oder geregelt werden sollte. Die Steuerung oder Regelung der Zwischenkreisspannung U_ZK kann hierbei indirekt durch eine geeignete Wahl der elektrischen Leistung P_EM und der Leistung P_NV eingestellt werden. Hierbei besteht allerdings das Problem, dass nur drei zu regelnde Größen (P_EM, P_NV, U_ZK) mit einer Steuereinheit, die letztendlich nur die Leistung P_NV und die Leistung P_EM einstellen kann, zu regeln sind. Dieses Problem ist durch die Strategieeinheit 11 gelöst. Diese kann, abhängig von einer jeweiligen Betriebssituation, einer Priorisierung der Regelgrößen vornehmen. Dies kann auch als Optimierungsproblem aufgefasst werden, bei dem sich eine Gütefunktion betriebssituationsabhängig ändert. Hierbei bestimmt die Strategieeinheit 11 einen gewünschten Sollstrom i_L,soll durch die Induktivität L und ein Sollmoment M_soll abhängig von einer aktuellen Zwischenkreisspannung U_ZK, einer aktuellen Batteriespannung Ubatt und weiteren Eingangsgrößen, von denen exemplarisch eine Fahrpedal-Stellung FP und eine Bremspedalstellung BP dargestellt sind.Similarly to the interference variables, the power P _ZK transmitted to the intermediate circuit capacitor C _ZK cannot be set independently of the other powers specified in formula 1. However, the intermediate circuit voltage U _{ZK overhangs} $${\text{i}}_{\text{CC}}={\text{P}}_{\text{CC}}/{\text{u}}_{\text{CC}}$$

and $${\text{you}}_{\text{CC}}/\text{German}=1/{\text{C}}_{\text{CC}}\times {\text{i}}_{\text{CC}}$$

depends on the power P _ZK . If, for example, the intermediate circuit voltage U _{ZK exceeds} a permissible upper limit of the intermediate circuit voltage U _ZK , the intermediate circuit capacitor C _ZK and/or circuit breakers S1, . . . , S6 can be destroyed. If the intermediate circuit voltage U _ZK falls below a value of 2×Ubatt, for example, then the electric machine can only be operated with limited power and/or torque fluctuations can occur. It follows from this that the intermediate circuit voltage U _ZK should preferably also be controlled or regulated. In this case, the control or regulation of the intermediate circuit voltage U _ZK can be adjusted indirectly by a suitable selection of the electrical power P _EM and the power P _NV . However, there is the problem here that only three variables to be regulated (P _EM , P _NV , U _ZK ) have to be regulated with a control unit which ultimately can only set the power P _NV and the power P _EM . The strategy unit 11 solves this problem. Depending on the respective operating situation, this can prioritize the controlled variables. This can also be understood as an optimization problem in which a quality function changes depending on the operating situation. In this case, strategy unit 11 determines a desired target current i _L, target through inductance L and a target torque M target as a function of a current intermediate circuit voltage U _{ZK ,} a current battery voltage Ubatt and other input variables, of which an accelerator pedal position FP and a brake pedal position BP are shown as examples are.

This results in a control hierarchy with a total of four levels. In a top level of the control hierarchy, strategy unit 11 determines a desired setpoint current i _{L, setpoint} and a desired setpoint torque M setpoint for electric machine 6. In a second level, unit 10 determines a first average phase voltage U _P1M and unit 12 determines motor voltages U _S1 , U _S2 , U _S3 . In a third level of the control hierarchy, the unit 13 determines setpoint phase voltages U _P1, set , U _{P2,set ,} U _P3, set . In a fourth and last level of the control hierarchy, units 14 determine the switching times of the power switches S1, ..., S6 of the half-bridges of the converter 7.

Some operating situations are considered below as examples.

• Hierbei dient das Element zur Spannungswandlung, insbesondere die Induktivität L und die Leistungsschalter S1, S2, als Aufwärtswandler, dessen Funktion vorhergehend in den Erläuterungen zu 2 dargestellt wurde. Die Leistungsschalter S3, ..., S6 können hierbei geöffnet bleiben. Alternativ können die ersten Leistungsschalter S3, S5 der zweiten und dritten Halbbrücke synchron zu dem ersten Leistungsschalter S1 der ersten Halbbrücke und die zweiten Leistungsschalter S4, S6 der zweiten und dritten Halbbrücke synchron zu dem zweiten Leistungsschalter S2 der ersten Halbbrücke angesteuert werden. Hierdurch ändert sich ein Zustand der stehenden und unbestromten Elektromaschine 6 nicht, da die Differenz-Klemmen-Spannungen U_K1-K2, U_K1-K3, U_K2-K3 Null sind. Die Strategieeinheit 10 bestimmt ein Sollmoment M_soll = 0 und eine Soll-Zwischenkreisspannung U_ZK,soll von z.B. 2 x U_batt. Ein Sollstrom i_L,_soll, insbesondere eine Stromstärke des Sollstroms i_L,_soll, kann dann z.B. auf einfache Weise mittels eines P-Reglers vorgegeben werden. Beispielsweise kann i_L,soll gemäß

$${\text{I}}_{\text{L},\text{soll}}={\text{P}}_{\text{const}}\times \left({\text{U}}_{\text{Zk},\text{soll}}-{\text{U}}_{\text{ZK}}\right)$$

mit einem Verstärkungsfakt P_const kleiner Null bei der in 2 dargestellten Richtung des Stromes iL in 2 sein.Structure of an intermediate circuit voltage U _ZK with a stationary, torque-free electric machine 6:

• In this case, the element for voltage conversion, in particular the inductance L and the power switches S1, S2, serves as a step-up converter, the function of which was previously explained in the explanations for 2 was presented. The circuit breakers S3, ..., S6 can remain open in this case. Alternatively, the first power switches S3, S5 of the second and third half bridges can be driven synchronously with the first power switch S1 of the first half bridge and the second power switches S4, S6 of the second and third half bridges can be driven synchronously with the second power switch S2 of the first half bridge. As a result, a state of the stationary and unenergized electric machine 6 does not change, since the differential terminal voltages U _K1-K2 , U _K1-K3 , U _K2-K3 are zero. Strategy unit 10 determines a setpoint torque M _setpoint =0 and a setpoint intermediate circuit voltage U _{ZK,set of,} for example, 2×U _batt . A target current i _L , target _, in particular a current intensity of the target current i _L , target _, can then be specified in a simple manner, for example, by means of a P controller. For example, i _L,soll according to

$${\text{I}}_{\text{L},\text{target}}={\text{P}}_{\text{const}}\times \left({\text{u}}_{\text{Zk},\text{target}}-{\text{u}}_{\text{CC}}\right)$$

with a gain factor P _const less than zero at the in 2 shown direction of the current iL in 2 be.

Tempering:

This results in two control scenarios. If a maximum torque that can be set is limited by the properties of the electric machine 6, then the setpoint torque M setpoint _is set to this maximum possible torque. The strategy unit 10 then determines a setpoint current i _L ,nom _, with which the intermediate circuit voltage U _{ZK is also regulated to a predetermined setpoint intermediate circuit voltage U ZK,} nom (see formula 16). If a maximum torque that can be set is not limited by the properties of the electric machine 6, but rather by a maximum power that can be drawn from the vehicle electrical system battery 4, then the strategy unit 10 determines the target current i _L, setpoint as the maximum permissible amount in relation to the in 2 Negative current direction shown, value i _{L,setpoint,max} . As a result, the electric machine 6 is supplied with as much energy as possible. The setpoint torque M setpoint can then _be specified in such a way that the intermediate circuit voltage U _{ZK is regulated to a predetermined setpoint intermediate circuit voltage U ZK,} setpoint, in the simplest case by means of a P controller according _to formula 16. If the setpoint torque M setpoint reaches a maximum permissible value or if the intermediate circuit voltage U _ZK approaches its maximum permissible value, the strategy unit can reduce the amount of the setpoint current i _L, setpoint in terms of amount. In both scenarios, the battery voltage Ubatt can also be detected, with the amount of the current i _L, setpoint being reduced when the battery voltage Ubatt falls below a lower limit. As a result, an optimal power point of the vehicle electrical system battery 4 can be set in an advantageous manner.

recuperate:

Similar to starting, different control scenarios can also be used in recuperation mode. If the maximum possible negative torque is not limited by the properties of the electric machine 6, the strategy unit 10 can set a maximum permissible, in relation to the 2 shown current direction of the current iL positive, target current i _L,soll output. Here, the vehicle electrical system battery 4 withdraws as much electrical energy as possible from the electric machine 6 operated as a generator. In this case, setpoint torque M set can _be specified in such a way that intermediate circuit voltage U _{ZK is regulated to a specified set intermediate circuit voltage U ZK,} set , which in turn can be done using a simple P rule according to formula 16. If the setpoint torque M _setpoint reaches a minimum permissible value or the intermediate circuit voltage U _ZK approaches a minimum permissible value, the setpoint current i _L, setpoint can be reduced in terms of absolute value by the strategy unit. In this case too, the battery voltage Ubatt can also be detected and, if the battery voltage Ubatt exceeds an upper limit, the amount of the setpoint current i _L, setpoint can be reduced. If the maximum torque that can be set is determined by properties of the electric machine, then the setpoint torque M setpoint _{should be} set to this maximum torque.

Of course, other operating situations, e.g. traction help, stall protection, a so-called engine boost function, discharging of the intermediate circuit capacitor C _ZK into the vehicle electrical system battery 4 at the end of the journey and a normal generator function without limitation can also be implemented using the device according to the invention and the method according to the invention .

In the previous statements, the vehicle electrical system battery 4 was considered the only energy source by means of which the electric machine 6 can be supplied with electrical energy during motor operation. In this case, the intermediate circuit capacitor C _ZK can be regarded as a smoothing capacitor which can absorb or output maximum power in the millisecond range at best. It does not make sense here to design the electric machine for significantly greater power than the vehicle electrical system battery 4 short can pick up or give away on time. Optionally, what is known as a thin-film capacitor can also be connected in parallel with the intermediate circuit capacitor C _ZK . In a matter of seconds, this can then absorb or deliver similar or even greater power than the vehicle electrical system battery 4 . The electric machine 6 can thus be designed for higher powers than the powers that can be output or absorbed by the vehicle electrical system battery 4 for a short time. In this case, it may be necessary to design the circuit breakers S1, ..., S6 for larger currents.

An energy content of a capacitor depends quadratically on a voltage drop across the capacitor. $$\text{E}=0.5\times \text{C}\times \text{u}\times \text{u}$$

Corresponding to the previously explained operating situation of a build-up of an intermediate circuit voltage U _ZK with a stationary, torque-free electric machine, the thin-film capacitor can be charged to as high an energy content as possible in such an arrangement. As a result, for at least one motor high-load case, such as a cold start of a diesel engine, electrical power can be made available for a short time, which exceeds the maximum power available from the vehicle electrical system battery 4 . In such a case, the strategy unit 10 would specify a desired intermediate circuit voltage U _ZK,soll close to a maximum permissible value (eg 4×U _batt, in this case approx. 48 V). In addition, strategy unit 10 could limit setpoint current i _L, setpoint to a minimum permissible (negative) value.

During a starting process explained above, a device that also includes a thin-film capacitor can be controlled in such a way that strategy unit 10 requests a maximum permissible target torque _Msoll and a minimum permissible target current iL _,soll . The thin-film capacitor can deliver the electrical power that is required in addition to the power delivered by the vehicle electrical system battery 4, with the intermediate circuit voltage U _ZK dropping. In a case of recuperation, analogously to the recuperation mode explained above, the strategy unit can request a relatively low target intermediate circuit voltage U _ZK, setpoint (eg 2×U _batt ) at the start of recuperation mode. In the case of sufficiently strong braking, the strategy unit would then request a maximum setpoint current i _L, setpoint and a minimum setpoint torque M setpoint _, ie maximum amount in terms of amount as a generator. The electrical power that the vehicle electrical system battery 4 cannot absorb is stored in the thin-film capacitor. In order not to have to abruptly reduce the braking torque when the maximum value of the intermediate circuit voltage U _ZK is reached, it can be useful for the strategy unit _to start setting the target torque M target from a predetermined threshold of the intermediate circuit voltage U _ZK , e.g. at 90% of a maximum intermediate circuit voltage U _ZK to reduce in amount. After the end of braking, the strategy unit 11 can leave the setpoint current i _L, setpoint at a high setpoint value in order to prepare the intermediate circuit voltage U _ZK for any further recuperation.

Electrical wiring of electric machines is conceivable in which the previously explained motor voltages U _S1 , U _S2 , U _S3 are not explicitly as in 2 Device 1 shown are available. With electric machines connected in this way, a desired mode of operation (speed, torque) of the electric machine and the phase voltages U _{P1 ,} U _P2 , U _P3 to be set for this or the switching times of the circuit breakers S1, . . . , S6 are determined directly. In addition to the setpoint torque M setpoint and possibly other measured variables, the intermediate circuit voltage U _ZK can also usually _be specified. If the phase voltages U _{P1 ,} U _P2 , U _P3 are not available, but only pulse duty factors, they can be converted into phase voltages U _{P1 ,} U _P2 , U _P3 according to formula 6. Calculation methods are specified below with which calculated phase voltages U _{P1 ,} U _P2 , U _P3 of any electric machine can be converted into motor voltages U _S1 , U _S2 , U _S3 according to the invention.

In a first case, half of the intermediate circuit voltage U _ZK is subtracted from the predetermined phase voltages U _P1 , U _P2 , U _P3 in order to obtain the motor voltages U _S1 to U _S3 . If the average values over time of the motor voltages U _S1 , U _S2 , U _S3 calculated in this way are equal to or close to zero for an electric machine 6 operated at a constant operating point, correct operation of the electric machine is possible using the method according to the invention.

In a second alternative, a mean value can be determined from the phase voltages U _P1 to U _P3 and subtracted from the respective phase voltages U _P1 , U _P2 , U _P3 in order to obtain the motor voltages U _S1 , U _S2 , U _S3 .

Reference List

1

Device for energy transfer

2

low voltage range

3

high voltage area

4

on-board battery

5

electrical consumers

6

electric machine

7

converter

8th

Voltage conversion element

10

Unit for determining an average phase voltage

11

strategy unit

12

Unit for determining at least one motor voltage

13

Unit for determining a target phase voltage

14

Unit for determining switching times

Ubatt

battery voltage

UCC

intermediate circuit voltage

UP1

first phase voltage

UP2

second phase voltage

UP3

third phase voltage

US1

first motor voltage

US2

second motor voltage

US3

third motor voltage

L

inductance

UL

voltage across the inductor

UP1M

first mean phase voltage

UP1, set

first target phase voltage

UP2, should

second target phase voltage

UP3, should

third target phase voltage

iNV

low voltage range current

ibat

battery power

iL

current through the inductance

iHV

High Voltage Range Electricity

iZK

intermediate circuit current

iP1

first phase current

iP2

second phase current

iP3

third phase current

iL, should

Target current through the inductor

S1

first power switch of the first half-bridge

S2

second power switch of the first half-bridge

S3

first power switch of the second half-bridge

S4

second power switch of the second half-bridge

S5

first power switch of the third half-bridge

S6

second power switch of the third half-bridge

D1

diode

D2

diode

D3

diode

D4

diode

D5

diode

D6

diode

S7

first circuit breaker of the voltage conversion element

S8

second power switch of the voltage conversion element

D7

diode

D8

diode

K1

first terminal of the electric machine

K2

second terminal of the electric machine

K3

third terminal of the electric machine

S

star point

ML1

first motor inductance of the electric machine

ML2

second motor inductance of the electric machine

ML3

third motor inductance of the electric machine

FP

accelerator pedal sensor signal

bp

Brake pedal sensor signal

Msoll

target torque

a

rotor position

Ω

rotational speed

TS1

Switching time of the first circuit breaker of the first half bridge

TS2

Switching time of the second power switch of the first half bridge

Claims (9)

Device for energy transmission in a motor vehicle, the motor vehicle having an on-board network, the on-board network having at least one low-voltage area (2) with a first voltage level, the device (1) having at least one electric machine (6), a converter assigned to the electric machine (6). (7), at least one intermediate circuit capacitor (C _ZK ), at least one energy store assigned to the low-voltage range, at least one element for voltage conversion and at least one control unit, wherein the electric machine (6) can be operated in motor mode or generator mode, the Converter (7) has at least one half-bridge with two power switches (S1, S2, S3, S4, S5, S6), wherein a section between the power switches (S1, S2, S3, S4, S5, S6) via a first supply path with a Terminal (K1, K2, K3) of the electric machine (6) is electrically connected, wherein the element for voltage conversion mi at least two power switches (S1, S2, S3, S4, S5, S6, S7, S8) and at least one inductor (L), the power switches of the voltage conversion element being the power switches (S1, S2, S3, S4, S5, S6 ) of the at least one half-bridge of the converter (7), wherein the at least one inductance (L) of the element for voltage conversion in a second supply path that connects the low-voltage range (2) and that between the power switches (S1, S2, S3, S4, S5 , S6) electrically connects the half-bridge section of the half-bridge, is arranged, wherein the second supply path is different from the first supply path, characterized in that the device (1) has a unit (10) which is designed in such a way to determine at least one mean phase voltage (U _P1M ) a mean phase voltage (U _P1M ) of converter (7) at least as a function of a desired power (P _NV ) to be transmitted into or out of the low-voltage range (2), the device (1) further having at least one unit (12). , which is designed in such a way to determine at least one motor voltage ( _{US1, US2 , US3} ) of the electric machine (6) a motor voltage ( _{US1, US2 , US3} ) of the electric machine (6) at least as a function of a desired electrical To determine power (P _EM ) of the electric machine (6), wherein the device (1) further comprises at least one unit (13) which is designed to determine at least one Target phase voltage ( _UP1,setup , U _P2,setup, U _P3,setup ) a set phase voltage ( _UP1,setup , U _P2,setup, U _P3,setup ) of the converter (7) at least as a function of the average phase voltage (U _P1M ) and the motor voltage (U _S1 , U _S2 , U _S3 ), the control unit switching the circuit breakers (S1, S2, S3, S4, S5, S6) of the converter (7) depending on the setpoint Phase voltage (U _P1,soll , U _P2,soll, U _P3,soll ) controls. device after claim 1 , characterized in that in the motor operation of the electric machine (6) an energy supply of the electric machine (6) can be guaranteed exclusively from the energy store. Device according to one of Claims 1 or 2 , characterized in that the converter (7) is designed as a three-phase converter (7), each phase of the converter (7) being assigned a half-bridge each with two circuit breakers (S1, S2, S3, S4, S5, S6), wherein a section between the power switches (S1, S2, S3, S4, S5, S6) of each half-bridge is electrically connected via first supply paths to a respective terminal (K1, K2, K3) of a three-phase electrical machine (6), the element for voltage conversion being 6 Circuit breakers (S1, S2, S3, S4, S5, S6) and 3 inductances (L1, L2, L3), with the 6 circuit breakers (S1, S2, S3, S4, S5, S6) each containing the 2 circuit breakers (S1, S2, S3, S4, S5, S6) of the half-bridges of the converter (7), in each case one inductance (L1, L2, L3) of the element for voltage conversion being arranged in second supply paths, the second supply paths covering the low-voltage range (2) and between the circuit breakers (S1, S2, S3, S4, S5, S6 ) electrically connect the respective half-bridge lying section of the respective half-bridge and are different from the first supply paths. Device according to one of the preceding claims, characterized in that the power switches (S1, S2, S3, S4, S5, S6) of the converter (7) are switched by means of the control unit as a function of at least one desired electrical power (P _EM ) of the electric machine and a desired power (P _NV ) to be transmitted into or out of the low-voltage range (2) can be controlled. Device according to one of the preceding claims, characterized in that the vehicle electrical system additionally has at least one high-voltage area (3). Method for energy transmission in a motor vehicle, the motor vehicle having an on-board network, the on-board network having at least one low-voltage area (2) with a first voltage level, the motor vehicle having at least one electric machine (6), a converter (7) assigned to the electric machine (6) , at least one intermediate circuit capacitor (C _ZK ), at least one energy store assigned to the low-voltage range, at least one element for voltage conversion and at least one control unit, with the electric machine (6) being operated in motor mode or generator mode, with the converter (7 ) has at least one half-bridge with two power switches (S1, S2, S3, S4, S5, S6), with a section between the power switches (S1, S2, S3, S4, S5, S6) having a first supply path with a terminal (K1 , K2, K3) of the electric machine (6) is electrically connected, wherein the element for voltage conversion at least at least two power switches (S1, S2, S3, S4, S5, S6, S7, S8) and at least one inductor (L), the power switches of the voltage conversion element being the power switches (S1, S2, S3, S4, S5, S6 ) of the at least one half-bridge of the converter (7), the at least one inductance (L) of the element for voltage conversion being arranged in a second supply path, which electrically connects the low-voltage area (2) and the section of the half-bridge lying between the power switches of the half-bridge is, wherein the second supply path is different from the first supply path, wherein in the generatori During operation, the control unit controls the power switches (S1, S2, S3, S4, S5, S6) of the voltage conversion element in such a way that the electrical energy generated by the electric machine (6) is at least partially transferred into the low-voltage range, with the Control unit controls power switches (S1, S2, S3, S4, S5, S6) of the element for voltage conversion in such a way that electrical energy stored in the energy store is at least partially transmitted to the electric machine, characterized in that a unit (10) for determining at least an average phase voltage (U _P1M ) determines an average phase voltage (U _P1M ) of the converter (7) at least as a function of a desired power (P _NV ) to be transmitted into the low-voltage range (2) or out of the low-voltage range (2), wherein at least one unit (12) for determining at least one motor voltage (U _S1 , U _S2 , U _S3 ) of the Ele electric machine (6) determines a motor voltage (U _S1 , U _S2 , U _S3 ) of the electric machine (6) at least as a function of a desired electrical power (P _EM ) of the electric machine (6), with at least one unit (13) for determining at least one Target phase voltage ( _UP1,setup , U _P2,setup, U _P3,setup ) a set phase voltage ( _UP1,setup , U _P2,setup, U _P3,setup ) of the converter (7) at least as a function of the average phase voltage (U _P1M ) and the motor voltage (U _S1 , U _S2 , U _S3 ), the control unit switching the circuit breakers (S1, S2, S3, S4, S5, S6) of the converter (7) as a function of the setpoint phase voltage (U _P1,set , U _P2,set, U _P3,set ) controls. procedure after claim 6 , characterized in that a desired power (P _NV ) to be transmitted into or out of the low-voltage range (2) and a desired electrical power (P _EM ) of the electric machine from a strategy unit (11) at least in Depending on an intermediate circuit voltage (U _ZK ) and/or at least one driving-dynamics sensor signal and/or at least one driving-specific sensor signal (FP, BP) is determined. Procedure according to one of Claims 6 or 7 , characterized in that the unit (13) for determining at least one target phase voltage (U _P1, target , U _{P2, target ,} U _P3, target ) the at least one target phase voltage (U _P1, target , U _P2, target U _P3,soll ) as a function of a speed (Ω) of the electric machine (6). procedure after claim 8 , characterized in that the unit (13) for determining at least one target phase voltage (U _P1, target , U _{P2, target ,} U _P3, target ) the at least one target phase voltage (U _P1, target , U _P2, target U _P3,soll ) determined according to a first and a second operating mode, depending on the speed (Ω) is switched between the first and the second operating mode, with switching being a hard switch or a hysteresis-based switch or a fade-based switch.

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