Method for operating an energy converter, energy converter for electrically coupling a DC electrical system with an electric machine, and motor vehicle

Abstract

The invention relates to a method for operating an energy converter (10, 12, 14, 16, 18) for electrically coupling a first DC electrical system (20) with an electric machine (22), wherein the electric machine has a stator winding (26) with at least two phase windings (28, 30, 32) which is coupled via a respective first switching element (34, 36, 38) to a positive potential (52), via a respective second switching element (40, 42, 44) to a negative potential (54) and via a respective third switching element (46, 48, 50) to an intermediate electrical potential (56).According to the invention, the third switching elements each have two anti-series connected switching element transistors (64, 66) which are electrically connected to each other at a central terminal (68, 70, 72), wherein at least between two central terminals a primary winding (76, 78, 80, 98) of a transformer (82, 84, 86, 88) is connected, wherein the switching element transistors are operated in such a way that they are subjected to voltage pulses.

Description

[0001] The invention relates to a method for operating an energy converter, wherein a first DC electrical system is electrically coupled to an electric machine via the energy converter, wherein the energy converter has a DC intermediate circuit electrically coupled to the first DC electrical system, wherein the electric machine has a stator winding with at least two phase windings, wherein each phase winding is coupled to a positive electrical potential of the DC intermediate circuit via at least one respective first switching element of the energy converter, to a negative electrical potential of the DC intermediate circuit via at least one respective second switching element of the energy converter, and to an intermediate electrical potential of the DC intermediate circuit via at least one respective third switching element of the energy converter, depending on the respective switching states of the switching elements.wherein the positive electrical potential is greater than the intermediate electrical potential and the intermediate electrical potential is greater than the negative electrical potential, wherein the switching elements are operated in a switching mode depending on predetermined phase voltages for the respective phase windings. The invention further relates to an energy converter for electrically coupling a first DC electrical system to an electric machine, wherein the energy converter has a DC intermediate circuit electrically coupled to the first DC electrical system, wherein the electric machine has a stator winding with at least two phase windings, with respective first switching elements for electrically coupling a respective phase winding to a positive electrical potential of the DC intermediate circuit depending on the respective switching states of the first switching elements.The invention comprises two switching elements for electrically coupling a respective phase winding to a negative electrical potential of the DC link, depending on the respective switching states of the second switching elements; two switching elements for electrically coupling a respective phase winding to an intermediate electrical potential of the DC link, depending on the respective switching states of the third switching elements, wherein the positive electrical potential is greater than the intermediate electrical potential and the intermediate electrical potential is greater than the negative electrical potential; and a control unit configured to operate the switching elements in a switching mode depending on predefinable phase voltages for the respective phase windings. Finally, the invention also relates to a motor vehicle with an electric machine having a stator winding with at least two phase windings.a first and a second DC electrical system, as well as a power converter for electrically coupling the DC electrical systems and the electric machine.

[0002] Methods of the generic type, energy converters of the generic type, and motor vehicles of the generic type are extensively known in the prior art, so that a separate printed proof is not fundamentally necessary. Energy converters, also called energy transformers or the like, serve to electrically couple electrical networks, in particular vehicle electrical systems, and electrical equipment to one another so that energy exchange can take place. Preferably, the energy converter enables energy exchange in a bidirectional direction, at least with respect to the electric machine. This makes it possible to operate the electric machine in both motor and generator modes. The energy converter therefore also provides bidirectional energy coupling, at least for the first DC vehicle electrical system.

[0003] The first DC electrical system can, for this purpose, include an energy storage device, in particular a battery, such as a vehicle battery or similar in a motor vehicle. However, the DC electrical system can also include other energy sources or sinks.

[0004] The stator winding of an electric machine is typically supplied with alternating current. The electric machine can therefore be, for example, a synchronous machine, an asynchronous machine, or the like. The stator winding has at least two phase windings. However, a stator winding with three phase windings is widely used. The phase windings are supplied with corresponding alternating currents that have essentially the same frequency. However, the phase currents are phase-shifted relative to each other. In a stator winding with three phase windings, the phase currents are each shifted in phase by approximately 120° relative to each other. Therefore, the power converter typically provides the functionality of an inverter with regard to the coupling between the first DC electrical system and the electric machine.The inverter or energy converter has a DC intermediate circuit that is electrically coupled to, or can be coupled to, the first DC on-board network.

[0005] Furthermore, the energy converter provides a DC / DC converter capability, allowing the first DC electrical system to be electrically coupled to the second. Such an energy converter is particularly suitable for use in vehicles that are at least partially electrically powered. In such a vehicle, the electric motor can be part of an electric drivetrain that propels the vehicle during normal driving operation. It is now common practice in electrically powered vehicles for the first DC electrical system to operate at a relatively high DC voltage, especially a high-voltage DC voltage. High voltage refers to a DC voltage greater than approximately 60 V, specifically a DC voltage that complies with the ECE R 100 standard.A direct current voltage lower than approximately 60 V is referred to here as low-voltage direct current. Electrically powered vehicles often have a second DC electrical system, which is also a low-voltage system. The function of the first and second DC electrical systems in an electrically powered vehicle is well known to those skilled in the art, so further explanation is omitted here.

[0006] In the prior art, it is common practice for the energy converter to use an inverter for electrically coupling the first DC electrical system to the electric machine. The function of the inverter for coupling the first DC electrical system to the electric machine is also known to those skilled in the art, which is why detailed explanations in this regard are omitted here.

[0007] To electrically couple the first and second DC electrical systems, the prior art provides for a corresponding energy converter, in particular a DC / DC converter. In this context, CN 108 512 407 A discloses a pre-charging circuit, a control method for this circuit, and a converter. Furthermore, DE 10 2012 204 108 A1 discloses a power electronic arrangement with synchronization of a voltage node in the intermediate circuit.

[0008] Overall, this state-of-the-art design has proven its worth, but it also proves to be costly.

[0009] The invention is based on the objective of reducing the effort required for the energy converter.

[0010] The invention proposes a method, an energy converter and a motor vehicle according to the independent claims as a solution.

[0011] Advantageous further training opportunities arise from the characteristics of the dependent requirements.

[0012] With regard to a generic method, it is particularly proposed that the third switching elements each have two anti-series connected switching element transistors which are electrically connected to each other at a central terminal of the respective third switching element, wherein at least between the two central terminals of two selected third switching elements a primary winding of at least one transformer is connected, wherein the switching element transistors of the selected third switching elements are operated in such a way that the primary winding is supplied with voltage pulses.

[0013] With regard to a generic energy converter, the invention particularly proposes that the third switching elements each have two anti-series connected switching element transistors which are electrically connected to each other at a central terminal of the respective third switching element, wherein at least between the two central terminals of two selected third switching elements a primary winding of at least one transformer is connected, wherein the control unit is additionally configured to operate the switching element transistors of the selected third switching elements in such a way that the primary winding is supplied with voltage pulses.

[0014] With regard to a motor vehicle of the type described, the invention specifically proposes that the energy converter be designed according to the invention.

[0015] The invention is based, among other things, on the idea that by appropriately operating the switching element transistors in switching mode, it is possible to apply voltage pulses to the primary winding of at least one transformer. For this purpose, it can be provided, for example, that the switching element transistors of the at least two selected switching elements are operated based on different clock rates or clock frequencies. For example, it can be provided that the clock rates are phase-shifted relative to each other by a predefinable value, or the like. Preferably, however, the clock rates on which the switching element transistors of the third switching element are operated in clock mode are essentially the same.In this way, it is possible for the switching element transistors of the at least two selected switching elements to assume their switching states differently from one another, so that the at least one primary winding of the at least one transformer can be supplied with voltage pulses accordingly. The deviation between the clock rates on which the switching operation for the switching element transistors of the two at least selected switching elements is based can be essentially constant. Furthermore, it is of course also possible for the clock rates to be varied. For example, it can be provided that the deviation between the clock rates depends on the energy or power to be supplied by the at least one transformer.

[0016] The invention enables the simple, electrically isolated provision of electrical energy by means of at least one transformer, which can then be used for any purpose. For example, it can be provided that a second DC electrical system of a motor vehicle, electrically coupled to a secondary winding of the at least one transformer, is electrically supplied with energy by means of the at least one transformer. In a motor vehicle, the first DC electrical system can, for example, be designed as a high-voltage system, which serves in particular to supply the electric drive train with electrical energy. In addition, the motor vehicle can have a second DC electrical system, which is preferably designed as a low-voltage system.The low-voltage electrical system can be connected to electrical devices that require less power for their intended operation compared to the electric drivetrain. Such electrical devices can include, for example, a navigation system, vehicle lighting, an infotainment system, electric windows, electric mirror adjustment, and / or the like.

[0017] The energy converter of the invention thus provides not only the functionality of an inverter for operating the electric machine, but also the function of an energy converter for supplying a vehicle electrical system or the like. The energy converter of the invention can therefore implement the coupling of vehicle electrical systems and an electric machine particularly cost-effectively and efficiently. This results in cost savings compared to the prior art.

[0018] The switching element transistors can be configured as bipolar transistors or field-effect transistors. A standard bipolar transistor, an insulated-gate bipolar transistor (IGBT), or a similar device can be used as the bipolar transistor. A junction field-effect transistor or a metal-oxide-semiconductor field-effect transistor (MOSFET) can be used as the field-effect transistor. Combinations of these transistors can also be used as switching element transistors, for example, in the form of a Darlington transistor or similar configuration.

[0019] The switching operation of a transistor means that, in the on-state, a very low electrical resistance is provided between the terminals forming the switching path, allowing a high current flow at a very low residual voltage. In the off-state, the transistor's switching path has a high resistance, meaning it provides a high electrical resistance, so that even at a high voltage applied to the switching path, there is essentially no current flow, or only a very small, often negligible, current flow. This differs from the linear operation of a transistor.

[0020] Since the energy converter provides the functionality of an inverter, the energy converter, and in particular the inverter provided by it, also includes a DC link. The DC link typically has at least one DC link capacitor, which supports the functionality with respect to the inverter. To achieve the desired functionality, the inverter provided by the energy converter of the invention is designed as a three-level inverter. The inverter thus provides three electrical potentials at its AC terminals, to which the stator winding and the phase windings of the electric machine are connected, depending on the switching states of the first, second, and third switching elements.It is important to note that the switching elements electrically coupled to each phase winding do not simultaneously assume the switched-on state. Rather, each winding terminal of a given phase winding is always electrically coupled to at most one electrical potential of the DC link by means of the respective first, second, and third switching elements. This can, of course, also create additional possibilities for providing voltage pulses, namely when, in a specific operating state, the two selected third switching elements happen to be in the switched-off state. In such a case, it is then possible to provide additional voltage pulses by appropriately switching on the respective switching element transistors. This proves particularly advantageous when there is a high energy demand that is to be supplied by at least one transformer.Preferably, at least one winding end of each phase winding is electrically connected to a first, a second and a third switching element.

[0021] To provide the intermediate potential, the DC link can have a separate power source. Alternatively, the intermediate potential can be provided by the intermediate link capacitor, for example, by forming the intermediate link capacitor as a series circuit with the intermediate potential connected to its center terminal. Of course, other possibilities are conceivable.

[0022] The DC link is electrically coupled to the first DC electrical system. This first DC electrical system can provide the intermediate potential in addition to the positive and negative electrical potentials. However, it is also possible for the intermediate potential to be provided by the power converter, as explained previously.

[0023] In a motor vehicle, the DC electrical system can include individual vehicle batteries. With regard to the first DC electrical system, the intermediate potential can therefore be provided by the vehicle battery. In this case, the vehicle battery thus serves not only to provide the positive and negative electrical potentials, but also the intermediate potential.

[0024] Regarding the coupling between the electric machine and the first DC electrical system, the energy converter is designed for bidirectional electrical coupling. This makes it possible to operate the electric machine not only as a motor but also as a generator. This proves advantageous when the electric machine is used to brake a vehicle, for example, when driving downhill. The electrical energy supplied by the electric machine in generator mode can then be fed to the first DC electrical system, such as the vehicle battery. Preferably, it can also be fed, at least partially, to the at least one transformer.

[0025] With regard to the at least one transformer, only a unidirectional energy flow is provided on the energy converter side. However, this should be sufficient for most applications, especially in a motor vehicle.

[0026] The at least one transformer can, of course, have more than just a single primary winding, for example, two, three, or even more primary windings. The number of primary windings is preferably chosen to correspond to the number of third-phase windings, or vice versa. In particular, if three third-phase windings are provided, meaning that the stator winding also has three phase windings, the at least one transformer can be designed as a three-phase transformer, for example, connected on the primary side in a delta or star configuration, with the respective center terminals of the third-phase windings connected. In principle, it is also possible, instead of a multi-phase primary winding in the at least one transformer, to choose a corresponding number of single-phase transformers, whose primary windings can be connected accordingly.

[0027] It is further proposed that the at least one transformer has at least one secondary winding electrically coupled to a rectifier unit, whereby a DC voltage is provided by the rectifier unit depending on the voltage pulses. This makes it possible to provide a second DC voltage by means of the energy converter, which can be electrically coupled to or form a second DC electrical system. This is particularly advantageous for use in motor vehicles, as it allows for the simple implementation or support of the low-voltage electrical system. Separate energy converters, especially DC / DC converters or the like, can be eliminated. This enables a particularly compact and efficient power supply solution, especially in motor vehicles.

[0028] It is further proposed that the switching states of the switching elements be determined based on a PWM switching pattern specified for each of the phase windings, in order to set a specific phase alternating current at each phase winding. The PWM switching patterns for the at least two phase windings are determined by comparing the respective phase alternating voltages assigned to the phase windings with corresponding reference alternating voltages. In this way, the desired switching operation of the switching element transistors, as well as the switching elements as a whole, can be achieved with minimal effort. Determining the PWM switching patterns can be implemented analogously using a suitably designed hardware circuit, digitally using a suitably designed digital circuit, or using a program-controlled computer unit and / or the like.

[0029] The control unit serves to control the switching states of the switching elements. The control unit can be implemented as a hardware circuit and / or a program-controlled computer unit. In particular, the control unit can provide corresponding switching signals for the switching element transistors, enabling them to operate in switching mode. By appropriately controlling the switching element transistors using the respective switching signals, the switching state of the third switching element can be achieved. For this functionality, each switching element transistor has an inverse diode connected in parallel to its switching path. The control unit is preferably designed to execute the PWM switching patterns and the control of the switching states of the switching elements essentially in real time.

[0030] Preferably, triangular or sawtooth AC voltages are used as reference AC voltages, the frequency of which is determined depending on a clock rate for the PWM switching patterns. This allows for particularly simple generation of the PWM switching patterns. By providing a phase difference between the reference AC voltages, a corresponding phase difference with respect to the switching operation of the switching element transistors can also be achieved, thus enabling simple adjustment of the voltage pulses. The phase difference can be selected depending on the electrical energy or power to be supplied by the at least one transformer. The control unit can be configured to adjust the phase difference based on a phase control signal.The phase control signal can be provided by another unit, which outputs the phase control signal depending on a required energy or power demand.

[0031] It is further proposed that the respective frequencies of the reference AC voltages be set. The frequencies can preferably be set essentially independently of one another. By setting or adjusting the frequencies relative to each other, it is possible to influence or adjust the voltage pulses. This is one way to adjust the electrical energy or power transmitted via the transformer of the power converter. Setting or adjusting the frequencies can be achieved, for example, using the control unit. It can be provided that each of the reference AC voltage frequencies has its own individually adjustable oscillator. The oscillators can be set, at least with respect to their respective frequencies, using the control unit. The oscillators can be designed separately.It is also possible that the control unit contains the oscillators.

[0032] Furthermore, it is proposed that a phase difference between the reference AC voltages be set. For example, it is possible to provide a first reference AC voltage using an oscillator. Subsequent reference AC voltages can be derived from the first reference AC voltage using a phase-shifting unit. The phase shift of the phase-shifting unit can be adjusted, at least with respect to its phase shift. For example, the phase shift of each phase-shifting unit can be set by the control unit. Alternatively or additionally, separate oscillators can be used for the reference AC voltages, preferably operated at approximately the same frequency, with phase differences being set by the control unit. Combinations with the aforementioned configurations are also possible.

[0033] Furthermore, it is proposed that the DC voltage and / or the electrical power supplied by the rectifier unit be adjusted depending on the phase difference between the reference AC voltages. In this way, control can be achieved by specifying the required electrical power or by measuring the DC voltage supplied by the rectifier unit. Based on this, the phase control signal can be provided, which serves to adjust the phase difference between the reference AC voltages. Preferably, it is provided that, in the case of more than two reference AC voltages, the phase difference between each successive reference AC voltage is also specified.

[0034] According to a further development, it is proposed that at least one transformer has a secondary winding electrically coupled to a rectifier unit in order to electrically couple a second DC electrical system via the rectifier unit. The transformer can have a single secondary winding. However, it can also be designed as a multi-phase transformer with a corresponding number of secondary windings, corresponding to the number of phases. Each secondary winding can be electrically connected to its own separate rectifier unit. For this purpose, the rectifier unit has a corresponding AC voltage connection that can be electrically coupled to the respective secondary winding. The rectifier units have DC voltage connections at which the rectified voltage is provided.The DC voltage connections can be connected to each other, for example in parallel, in series and / or the like.

[0035] According to a further embodiment, it is proposed that the stator winding has three phase windings, wherein the power converter has respective first, second, and third switching elements for each of the phase windings, and wherein the control unit is configured to operate the switching elements in switching mode depending on predefinable phase voltages for the respective phase windings, and wherein the at least one transformer has three primary windings electrically coupled to the respective center terminals. In this way, a particularly cost-effective system can be realized because electrical machines with stator windings having three phase windings are very common and inexpensive. At the same time, this embodiment makes it possible to use a suitably designed transformer, so that cost-effective components can also be used in this respect.This is particularly advantageous for use in a motor vehicle because an energy converter can be implemented cost-effectively.

[0036] Preferably, the at least one transformer has three secondary windings electrically coupled to a single rectifier unit. In this way, for example, a particularly cost-effective and simple rectifier unit can be implemented using a B6 diode circuit. However, it is also possible to provide separate rectifier units for the secondary windings. The rectifier unit can generally include diodes, thyristors, and / or similar components to perform the rectification function.

[0037] The advantages and effects described for the method according to the invention also apply equally to the energy converter and the motor vehicle according to the invention, and vice versa. In particular, method features can therefore also be formulated as device features and vice versa.

[0038] For use cases or application situations that may arise during the procedure and are not explicitly described here, it may be provided that, according to the procedure, an error message and / or a request for user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0039] The invention may also include the control unit for the energy converter. The control unit may comprise a data processing device or a processor unit or processor circuit configured to provide, in addition to controlling the switching element, at least one comparator function for the method according to the invention. For this purpose, the processor unit may comprise at least one microprocessor and / or at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor). In particular, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an NPU (Neural Processing Unit) may be used as the microprocessor.Furthermore, the processor device can include program code configured to perform the functionality required for carrying out the method according to the invention when executed by the processor device. The program code can be stored in a data memory of the processor device. The processor device can, for example, be based on at least one circuit carrier such as a circuit board and / or on at least one SoC (System on Chip).

[0040] The invention also includes further developments of the discharge circuit according to the invention, which have features already described in connection with the further developments of the method according to the invention. For this reason, the corresponding further developments of the discharge circuit according to the invention are not described again here.

[0041] The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.

[0042] The invention also includes combinations of the features of the described embodiments. The invention therefore also includes realizations that each exhibit a combination of the features of several of the described embodiments, provided that the embodiments have not been described as mutually exclusive.

[0043] The following are exemplary embodiments of the invention described. This is illustrated by: Fig. 1 a schematic circuit diagram of a two-level inverter of a motor vehicle according to Fig. 11, which is connected to a vehicle battery and to a three-phase electric machine of the motor vehicle according to Fig. 11 is connected, Fig. 2 a schematic circuit diagram of a three-level inverter, which is connected to a first DC electrical system and to the three-phase electric machine of the motor vehicle according to Fig. 11 is connected, Fig. 3 a schematic diagram representation in which a first of three phase voltages for a first phase winding of the stator winding of the three-phase electrical machine and a reference AC voltage for determining a PWM switching pattern for the inverter according to Fig. 1 or Fig. 2 is shown, Fig. 4 a schematic circuit diagram of the three-level inverter according to Fig. 2, wherein third switching elements comprise a series connection of two transistors each to form center terminals, wherein an isolating converter is connected to the center terminals to form a power converter, Fig. 5 a schematic diagram representation such as Fig. 3, in which a second of the three phase voltages is used for a second phase winding of the stator winding of the three-phase electrical machine and a second reference AC voltage is used to determine a PWM switching pattern for the energy converter according to Fig. 4 is shown, Fig. 6 a schematic diagram representation such as Fig. 3, wherein a third of the three phase voltages is used for a third phase winding of the stator winding of the three-phase electrical machine and a third reference AC voltage is used to determine a PWM switching pattern for the energy converter according to Fig. 4 is shown, Fig. 7 an excerpt of the schematic circuit diagram of the energy converter according to Fig. 4, in which a first embodiment for the isolation transformer is provided with a three-phase transformer and three rectifier units, Fig. 8 a schematic circuit diagram of the energy converter according to Fig. 4, in which a second embodiment for the isolation converter is provided with three single-phase transformers and three rectifier units, Fig. 9 a schematic circuit diagram of the energy converter according to Fig. 4, in which a third embodiment for the isolation transformer is provided with a three-phase transformer and a single rectifier unit, Fig. 10 a schematic circuit diagram of the energy converter according to Fig. 9, in which a fourth embodiment for the isolation transformer is provided with a three-phase transformer and a single rectifier unit, wherein a capacitor is connected in series to each of the primary windings, and Fig. 11 A schematic side view of a motor vehicle with an electric powertrain.

[0044] The exemplary embodiments described below are preferred embodiments of the invention. In these exemplary embodiments, the described components each represent individual features of the invention, which can be considered independently of one another and each further develops the invention independently. Therefore, the disclosure is intended to include combinations of features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0045] In the figures, identical reference symbols denote functionally equivalent elements.

[0046] Fig. Figure 11 shows a schematic side view of a motor vehicle 120 with an electric powertrain 122. The powertrain 122 has a vehicle battery 124 which is connected to a DC intermediate circuit 24 ( Fig. 4) an energy converter 10, 12, 14, 16, 18 is electrically coupled. The energy converter 10, 12, 14, 16, 18 is connected on the AC side to an electric machine 22, which serves to drive the motor vehicle 120 during normal operation. The electric machine 22 is designed as a three-phase asynchronous machine. In alternative configurations, a correspondingly different electric machine can of course be selected, for example a synchronous machine or the like. Likewise, the electric machine 22 can be designed for a different number of phases.

[0047] The energy converter 10, 12, 14, 16, 18 has the DC intermediate circuit 24 ( Fig. 2) which can be electrically coupled to the vehicle battery 124 via a switching unit (not shown), depending on the switching state of the switching unit. The vehicle battery 124 is designed as a high-voltage battery and provides a DC voltage of approximately 450 V.

[0048] During normal operation, the DC link 24 is electrically coupled to the vehicle battery 124, enabling the power converter 10, 12, 14, 16, 18 to convert the electrical energy from the vehicle battery 124 into an AC voltage suitable for the electric machine 22. The power converter 10, 12, 14, 16, 18 is designed for bidirectional electrical energy coupling or power coupling between the vehicle battery 124 and the asynchronous machine 22. For this purpose, the power converter 10, 12, 14, 16, 18 acts as an inverter.

[0049] Fig. Figure 1 shows a schematic circuit diagram of a two-level inverter 128, as used as an energy converter in motor vehicles according to Fig. 11 can be used. Such a two-level inverter 128 is disclosed, for example, in EP 2 863 528 A1. The inverter 128 is designed for three-phase operation and for this purpose has three respective first switching elements 34, 36, 38 and three respective second switching elements 40, 42, 44, which form respective series connections. The stator winding of the asynchronous machine 22 with its phase windings is connected to the center terminals of the series connections. In this embodiment, it is provided that the phase windings are connected in a star connection.

[0050] The vehicle battery 124 is part of a first DC electrical system 20 and is supplied with electrical energy by it. The first switching elements 34, 36, 38 are electrically coupled to a positive electrical potential 52 of the first DC electrical system 20, so that, depending on their switching states, the respective phase windings of the electric machine 22 can be coupled to the electrical potential 52. Similarly, the second switching elements 40, 42, 44 are coupled to a negative electrical potential 54 of the first DC electrical system 20, so that the corresponding ends of the phase windings can be coupled to the negative electrical potential 54, depending on the respective switching states.

[0051] The switching elements 34 to 44 are designed as MOSFETs, which are supplied with corresponding switching signals by a control unit (not shown) so that the MOSFETs can operate in switching mode and thus provide the switching states of the switching elements 34 to 44. It is provided that the respective switching elements 34 to 44 for each of the phases are operated in PWM mode, which is known in principle to those skilled in the art, therefore further explanations are omitted here.

[0052] Fig. Figure 2 shows a schematic circuit diagram of a three-level inverter 126, which is also connected to the electrical DC power supply 20 and to the asynchronous machine 22 of the motor vehicle 120 according to Fig. 11 is connected. In this embodiment, the inverter 126 utilizes an additional electrical potential, namely an intermediate potential 56. The intermediate potential 56 is smaller than the positive electrical potential 24, but larger than the negative electrical potential 54. Preferably, the intermediate potential 56 is set approximately midway between the positive and negative electrical potentials 52 and 54. For this purpose, the inverter 126 additionally has third switching elements 46, 48, and 50, which allow the respective phase windings 28, 30, and 32 of the stator winding 26 of the asynchronous machine 22 to be electrically coupled to the intermediate potential 56, depending on their switching states.

[0053] As from Fig. As can be seen in Figure 2, each of the third switching elements 46, 48, 50 has two anti-series connected switching element transistors 64, 66, which in this case are also formed by MOSFETs. The switching element transistors 64, 66 form the respective center terminals 68, 70, 72 of the respective third switching elements 46, 48, 50. This configuration of the third switching elements 46, 48, 50 allows a bidirectional off-state to be achieved, even though the third switching elements 46, 48, 50 are formed by transistors, specifically MOSFETs in this case. This is important to note because transistors typically have inverse diodes connected in parallel to their control path.

[0054] Out of Fig. 2 It is further evident that the inverter 126 has the DC intermediate circuit 24, which is connected to the vehicle battery 124 of the motor vehicle 120 according to Fig. 11 is electrically coupled. Furthermore, it is from Fig. 2. It is evident that the motor vehicle is in accordance with Fig. It may have 11 further electrical components, which are also connected to the first DC electrical system 20 and are directly supplied with the voltage of the vehicle battery 124, namely an electric heater 130, a high-voltage DC / DC converter 132, a low-voltage DC / DC converter 134 and an electric air conditioning compressor 136. Further components may be connected as required.

[0055] Fig. Figure 3 shows a schematic diagram representation of signal waveforms over time. Fig. Figure 3 shows a signal waveform of a first phase voltage 58 and a first reference AC voltage 104. By comparing the first phase voltage 58 with the first reference AC voltage 104, the PWM switching pattern can be determined for those switching elements that are electrically connected to the first phase winding 28, namely switching elements 34, 40, and 46. For the other two phase windings 30 and 32, a further phase voltage 60 and 62, respectively, is shown. Fig. 5, Fig. 6) specified, which is also compared with the first phase AC voltage 104 in order to determine the respective PWM switching patterns for the switching elements connected to the phase windings 30, 32. Determining the PWM switching patterns is also known to those skilled in the art, which is why further detailed explanations are omitted here. Determining the PWM switching patterns can be done at least partially using analog hardware or at least partially computer-aided using a program-controlled computer unit and / or the like.

[0056] Fig. Figure 4 shows a schematic circuit diagram of the three-level inverter 126 according to Fig. 2, wherein an isolating converter 74 is connected to the center terminals 68, 70, 72, thus forming an energy converter 10. The energy converter 10 therefore includes not only the functionality of the inverter 126, but also a further energy conversion functionality, namely that provided by means of the isolating converter 74. By appropriately operating the third switching elements 46, 48, 50, and in particular the switching element transistors 64, 66, it is possible to provide a voltage to, for example, power a second DC electrical system 112 ( Fig. 7 to Fig. 10) to provide or supply with electrical energy. This is made possible by not comparing the phase alternating voltages 58, 60, 62 to the same reference alternating voltage 104.

[0057] This shows Fig. 5 a schematic diagram representation such as Fig. 3, in which the second of the three phase voltages 60 for the second phase winding 30 of the stator winding 26 of the asynchronous machine 22 is compared with a second reference AC voltage 106. Fig. Figure 6 shows a schematic diagram representation of how Fig. 3, in which the third of the three phase voltages 62 for the third phase winding 32 of the stator winding 26 of the asynchronous machine 22 is compared with a third reference AC voltage 108. Depending on these comparisons, the respective PWM switching patterns are determined. Based on these PWM switching patterns, the respective switching elements 34 to 50 are operated so that the energy converter 10 according to Fig. 4 can provide the inverter functionality. The in the Fig. 3, Fig. 5 and Fig. The phase voltages 58, 60, 62 shown in Figure 6 correspond to those also used for inverter 126 according to Figure 6. Fig. 2 can be used. As from Fig. As can be seen in Figure 2, the switching elements 34 to 50 are controlled by means of a control unit 110 of the inverter 126.

[0058] Out of Fig. As can be seen in Figure 4, the switching elements 34 to 50, and in particular the switching element transistors 64 and 66, are controlled by a control unit 110 with respect to their respective switching states or switching operation. The control unit 110 serves to determine the respective PWM switching patterns, depending on predefined phase-alternating voltages 58, 60, and 62, which are compared with the phase-alternating voltage 104.

[0059] In contrast to the design of inverter 126 according to Fig. 2 is in the inverter function of the energy converter 10 according to Fig. 4. It is provided that the phase AC voltages 48, 60, 62 are not compared with a single reference AC voltage 104, but rather with individual reference AC voltages 104, 106, and 108, respectively. In the present case, it is provided that the phase voltage 58 is compared with the reference AC voltage 104, the phase voltage 60 with the reference AC voltage 106, and the phase voltage 62 with the reference AC voltage 108. The phase voltages 58, 60, and 62 are implemented as sinusoidal AC voltages, whereas the reference AC voltages 104, 106, and 108 are implemented as triangular voltages. The amplitudes of the AC voltages are approximately equal. In alternative embodiments, sawtooth AC voltages or similar waveforms can be used as reference AC voltages instead of triangular voltages.

[0060] The phase-alternating voltages 58, 60, 62 are phase-shifted by approximately 120° relative to each other. Similarly, the reference voltages 104, 106, 108 are phase-shifted relative to each other. However, the phase shift here does not need to be 120°. This results in the respective switching element transistors 64, 66 of the third switching elements 46, 48, 50 switching offset from each other, thus enabling voltage pulses between the center terminals 68, 70, 72. These voltage pulses can be used by means of the isolating transformer 74 to transfer electrical energy or electrical power from the first DC electrical system 20 to a second DC electrical system 112, as will be explained further below.

[0061] Fig. Figure 7 shows a section of the schematic circuit diagram of the energy converter according to Fig. 4, in which a first embodiment for the isolation transformer 74 is provided with a three-phase transformer 88 and three rectifier units 100 to form a power converter 12. This embodiment is based on the embodiment of the power converter 12 according to Fig. 4, which is why reference is made to the relevant explanations.

[0062] The transformer 88 has three primary windings 76, 78, 80, which are connected in a delta configuration to the center terminals 68, 70, 72. The transformer 88 also has secondary windings 90, 92, 94, which are electrically isolated from one another. Each of the secondary windings 90, 92, 94 is connected to an AC voltage side of a respective rectifier unit 100. On the DC voltage side, the rectifier units 100 are connected in parallel and provide a second DC electrical system 112.

[0063] Fig. Figure 8 shows a schematic circuit diagram of an energy converter 14, which is also based on the design of the energy converter 10 according to Fig. 4. In this second embodiment, a second configuration for the insulating transformer 74 is provided with three single-phase transformers 82, 84, 86 and three rectifier units 100. The transformers 82, 84, 86 each have primary windings 98 and secondary windings 96. The primary windings 98 are also connected in a delta configuration and are connected to the center terminals 68, 70, 72. Each of the secondary windings 96 is electrically isolated from the other secondary windings 96 and is connected to a respective AC voltage side of a respective rectifier unit 100. Here, too, the DC voltage sides of the rectifier units 100 are connected in parallel to realize the second DC electrical system 112.

[0064] Fig. Figure 9 shows a schematic circuit diagram of an energy converter 16, which is also based on the design of the energy converter 10 according to Fig. 4 is based on a third embodiment for the isolating converter 74 with a three-phase transformer 88 and a single rectifier unit 102. The circuit of the energy converter 16 is essentially based on the design of the energy converter 12 with regard to the transformer 88. Fig. 7, which is why reference is made to the relevant explanations.

[0065] In contrast to the design according to Fig. Figure 7 provides that the secondary windings 90, 92, 94 are also connected in a delta configuration and are connected to one AC voltage side of a single rectifier unit 102. The rectifier unit 102 is designed as a three-phase rectifier unit and can, for example, include a B6 diode circuit for rectification. The second DC power supply 112 is provided on the DC voltage side.

[0066] Fig. Figure 10 shows a schematic circuit diagram of an energy converter 18, which is based on the design of the energy converter 16 according to Fig. 9 is based on this, with only the differences being explained below. In contrast to the design of the energy converter 16 according to Fig. 9 is in the design of the energy converter 18 according to Fig.Figure 10 provides that each of the primary windings 75, 78, 80 has a capacitor 114, 116, 118 connected in series. This allows, for example, resonance effects to be achieved to improve functionality and / or increase performance. Furthermore, it makes it possible to largely avoid DC current flow through the primary windings under unfavorable PWM switching patterns.

[0067] The exemplary embodiments serve only to clarify the invention and are not intended to limit it.

Claims

[1] Method for operating an energy converter (10, 12, 14, 16, 18), wherein the energy converter (10, 12, 14, 16, 18) is electrically coupled to a first DC electrical system (20) and an electric machine (22), wherein the energy converter (10, 12, 14, 16, 18) has a DC intermediate circuit (24) electrically coupled to the first DC electrical system (20), wherein the electric machine (22) has a stator winding (26) with at least two phase windings (28, 30, 32), wherein each phase winding (28, 30, 32) is connected to a positive electrical potential (52) of the first DC electrical system (20) via at least one respective first switching element (34, 36, 38) of the energy converter (10, 12, 14, 16, 18). DC intermediate circuit (24), via at least one respective second switching element (40, 42, 44) of the energy converter (10, 12, 14, 16,18) is coupled to a negative electrical potential (54) of the DC link (24) and via at least one respective third switching element (46, 48, 50) of the energy converter (10, 12, 14, 16, 18) to an intermediate electrical potential (56) of the DC link (24) depending on the respective switching states of the switching elements (34, 36, 38, 40, 42, 44, 46, 48, 50), wherein the positive electrical potential (52) is greater than the intermediate electrical potential (56) and the intermediate electrical potential (56) is greater than the negative electrical potential (54), wherein the switching elements (34, 36, 38, 40, 42, 44, 46, 48, 50) are connected depending on predetermined phase voltages (58, 60, 62) for the respective phase windings (28, 30, 32) are operated in a switching operation, , characterized by, that the third switching elements (46, 48, 50) each have two anti-series connected switching element transistors (64, 66) which are electrically connected to each other at a center terminal (68, 70, 72) of the respective third switching element (46, 48, 50), wherein at least between the two center terminals (68, 70, 72) of two selected third switching elements (46, 48, 50) a primary winding (76, 78, 80, 98) of at least one transformer (82, 84, 86, 88) is connected, wherein the switching element transistors (64, 66) of the selected third switching elements (46, 48, 50) are operated such that the primary winding (76, 78, 80, 98) is supplied with voltage pulses. [2] Method according to claim 1, characterized by, that the at least one transformer (82, 84, 86, 88) has at least one secondary winding (90, 92, 94, 96) which is electrically coupled to a rectifier unit (100, 102), wherein an electrical DC voltage is provided by means of the rectifier unit (100, 102) depending on the voltage pulses. [3] Method according to any one of the preceding claims, characterized by , that the switching states of the switching elements (34, 36, 38, 40, 42, 44, 46, 48, 50) are determined depending on a PWM switching pattern specified for each of the phase windings (28, 30, 32) in order to set a respective phase alternating current at each of the phase windings (28, 30, 32), wherein the PWM switching patterns for the at least two phase windings (28, 30, 32) are determined by comparing the respective phase alternating voltages (58, 60, 62) assigned to the phase windings (28, 30, 32) with respective reference alternating voltages (104, 106, 108). [4] Method according to claim 3, characterized by , that triangular alternating voltages or sawtooth alternating voltages are used as comparison alternating voltages (104, 106, 108), the frequency of which is determined depending on a clock rate for the PWM switching patterns. [5] Method according to claim 3 or 4, characterized by , that the respective frequencies of the comparison alternating voltages (104, 106, 108) are set. [6] Method according to claims 3 to 5, characterized by , that a phase difference is set between the reference AC voltages (104, 106, 108). [7] Method according to any one of the preceding claims, characterized by , that the DC voltage and / or the electrical power that can be provided by means of the rectifier unit (100, 102) is set depending on a phase difference between the reference AC voltages (104, 106, 108). [8] Energy converter (10, 12, 14, 16, 18) for electrically coupling a first DC electrical system (20) with an electric machine (22), wherein the energy converter (10, 12, 14, 16, 18) has a DC intermediate circuit (24) electrically coupled to the first DC electrical system (20), wherein the electric machine (22) has a stator winding (26) with at least two phase windings (28, 30, 32), with - respective first switching elements (34, 36, 38) for electrically coupling a respective phase winding (28, 30, 32) with a positive electrical potential (52) of the DC intermediate circuit (24) depending on the respective switching states of the first switching elements (34, 36, 38), - respective second switching elements (40, 42, 44) for electrically coupling a respective phase winding (28, 30, 32) with a negative electrical potential (54) of the DC intermediate circuit (24) depending on the respective switching states of the second switching elements (40, 42, 44), - respective third switching elements (46, 48, 50) for electrically coupling a respective phase winding (28, 30, 32) with an intermediate electrical potential (56) of the DC link (24) depending on the respective switching states of the third switching elements (46, 48, 50), wherein the positive electrical potential (52) is greater than the intermediate electrical potential (56) and the intermediate electrical potential (56) is greater than the negative electrical potential (54), and - a control unit (110) which is designed to operate the switching elements (34, 36, 38, 40, 42, 44, 46, 48, 50) in a switching operation depending on predefinable phase voltages (58, 60, 62) for the respective phase windings (28, 30, 32), characterized by, that the third switching elements (46, 48, 50) each have two anti-series connected switching element transistors (64, 66) which are electrically connected to each other at a central terminal (68, 70, 72) of the respective third switching element (46, 48, 50), wherein at least between the two central terminals (68, 70, 72) of two selected third switching elements (46, 48, 50) a primary winding (76, 78, 80, 98) of at least one transformer (82, 84, 86, 88) is connected, wherein the control unit (110) is additionally configured to operate the switching element transistors (64, 66) of the selected third switching elements (46, 48, 50) in such a way that the primary winding (76, 78, 80, 98) is supplied with voltage pulses. [9] Energy converter according to claim 8, characterized by, that at least one transformer (82, 84, 86, 88) has a secondary winding (90, 92, 94, 96) which is electrically coupled to a rectifier unit (100, 102) in order to electrically couple a second DC electrical system (112) by means of the rectifier unit (100, 102). [10] Energy converter according to claim 8 or 9, characterized by, that the stator winding (26) has three phase windings (28, 30, 32), wherein the energy converter (10, 12, 14, 16, 18) has respective first, second and third switching elements (34, 36, 38, 40, 42, 44, 46, 48, 50) for each of the phase windings (28, 30, 32), wherein the control unit (110) is configured to operate the switching elements (34, 36, 38, 40, 42, 44, 46, 48, 50) in a switching operation depending on predefinable phase voltages (58, 60, 62) for the respective phase windings (28, 30, 32), wherein the at least one transformer (88) has three electrically coupled terminals (68, 70, 72) has primary windings (76, 78, 80). [11] Energy converter according to any one of claims 8 to 10, characterized by , that at least one transformer (88) has three secondary windings (90, 92, 94) which are electrically coupled to a single rectifier unit (102). [12] Motor vehicle (120) with an electric machine (22) having a stator winding (26) with at least two phase windings (28, 30, 32), a first and a second DC electrical system (20, 112), and a power converter (10, 12, 14, 16, 18) for electrically coupling the DC electrical systems (20, 112) and the electric machine (22), characterized by , that the energy converter (10, 12, 14, 16, 18) is designed according to one of the preceding claims 8 to 11.

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