Electric Drive System

Abstract

The present invention relates to an electric drive system for or in a motor vehicle, comprising at least one synchronous machine with a double rotor and distributed windings arranged in a stator core, the double rotor being made of a magnetic flux-transmitting material made of a solid material and the windings designed to be self-supporting for torque support, and at least one three-level or multi-level inverter circuit connected to the synchronous machine at a load output and designed to convert a DC voltage received at the supply side into an AC voltage capable of driving the synchronous machine via the load output, the inverter circuit having a controllable three-level or multi-level inverter.

Description

[Technical Field]

[0001] The present invention relates to electric drive systems for or in motor vehicles. [Background technology]

[0002] Electric machines with one stator and two rotatably coupled rotors, known as double-rotor machines (also known as multi-rotors, dual-rotors, etc.), can improve both torque density and electric drive efficiency compared to conventional electric machines with a single rotor. This is especially true because the so-called "yokeless" design eliminates the need for a magnetic return path in the stator, significantly reducing magnetic losses. Furthermore, the presence of two rotors essentially frees up space for field-excited magnets (in the case of permanent magnet synchronous machines, PSM) or conductor material (in the case of induction machines, IM, or electrically excited synchronous machines, ESM). Depending on the orientation of the magnetic field lines in the air gap, such machines can be divided into two groups: axial flux propagation (magnetic field lines parallel to the axis of rotation, known as axial flux machines) and radial flux propagation (magnetic field lines radially in the air gap, known as radial flux machines).

[0003] Axial-flux double-rotor machines are disclosed, for example, in patent documents DE 102015226105 A1 and DE 102013206593 A1. These machines are characterized by high torque and power density, but their manufacturing costs are high because the stator core requires highly complex shapes to be stamped or manufactured by powder metallurgy. As a result, these machines have not been mass-produced and are only used in niche applications requiring high power density, such as racing and aviation. Furthermore, the mechanical mounting concept of the stator windings only allows the use of single-tooth windings, which has corresponding disadvantages in terms of noise excitation.

[0004] In contrast, radial-flux double-rotor machines can use fundamentally established manufacturing methods for windings and laminated cores, making them suitable for mass production. However, a major and unresolved technical challenge is supporting the torque generated in the stator core. Due to the presence of rotating components on the inside and outside, the laminated stator core cannot be mounted (e.g., press-fit, screwed, or glued) to a fixed housing, as is typically the case. Therefore, torque must be directed and supported at the axial ends of the laminated stator core or stator windings. Various approaches have been proposed in the prior art for this purpose, but all of them have significant disadvantages in terms of functionality and / or cost.

[0005] Patent document EP 1 879 283 discloses one method of designing stator windings as so-called yoke windings. An annular laminated stator core has grooves on its inner and outer diameters, between which a tangentially acting magnetic return path (also called a stator yoke) exists. In this case, the forward and return conductors of each winding strand are guided in radially overlapping grooves and wound around the yoke. The stator yoke is axially accessible between the winding strands and can be fixed to the housing, for example, by an axial screw connection (as described, for example, in JP 2018-082600 A). The axial pressure of the screws ensures both torsional rigidity of the laminated core and torque support at the axial ends. The north and south poles of the rotor magnetic field are opposite each other. The disadvantage of this concept is that the magnetic flux must be conducted entirely through the return yoke located between the stator slots. On the other hand, this increases the weight of the laminated stator core and significantly increases iron losses. The magnetic field lines of both rotor fluxes are closed via a magnetic return path within the laminated stator core, which generates iron losses. Furthermore, all individual coils of the yoke winding must be connected in parallel or series in the area of ​​the winding head, resulting in conflicts with design space and torque support. However, the yoke-wound winding allows direct mechanical contact with the laminated stator core.

[0006] Significant weight and loss reductions can be achieved if the magnetization directions of the radially arranged magnets are aligned with the current direction of the conductors in the slots. In this case, the magnetic return path in the stator can be omitted, creating a so-called "yokeless" double-rotor machine with distributed winding. The magnetic field lines close on the rotor. Because the magnetic return path in the stator is unnecessary, such machines have very low weight and iron losses. However, distributed winding does not allow direct mechanical contact of the laminated stator cores for torque support. For example, PCT International Application Publication No. 2004 / 004098 describes a yokeless design with distributed winding.

[0007] Even in so-called "yokeless" designs, it can still be useful to provide a thin yoke for mechanically connecting the stator teeth, but this is not necessarily necessary from an electromagnetic standpoint. The term "yokeless" therefore refers to electromagnetic flux propagation in which no magnetic flux exists tangentially to the stator. However, in this case, the windings cannot be designed as yoke windings because the forward and return conductors of the winding strands are distributed radially around the circumference to form a distributed winding. This creates a winding head for the distributed winding, making axial access to the laminated core difficult. Furthermore, purely radial flux propagation precludes the use of axial metal screw connections, as they form conductor loops with significant mutually coupled magnetic flux and high additional current heat losses.

[0008] Regarding axial support, various auxiliary designs for torque support have been proposed in the prior art, as described, for example, in German Patent Application Publication No. 102010055030 or U.S. Patent Publication No. 7557486. The problem here is that electrically and / or magnetically conductive metals are not permitted to protrude into the magnetic flux transmission area, or can only do so to a very limited extent, significantly limiting the choice of material and geometric design. Alternatively, synthetic material components, adhesives, and / or cast materials can also be used in the magnetic flux transmission area. However, these materials make it very difficult to achieve the high demands regarding temperature stability and mechanical strength.

[0009] To operate such a double rotor machine for or in a motor vehicle, an inverter is provided with a DC voltage applied to the output of a suitable energy storage device.

[0010] An inverter is an electrical device that converts a DC voltage into an AC voltage. Such inverters are used, for example, in modern automobiles, in photovoltaics (solar inverters), as components of frequency converters, and in many other applications to generate a suitable AC voltage from a DC voltage. These inverters and their fields of application are generally known in a wide range of circuit variations, and a detailed description of their circuit design and operating modes is not necessary.

[0011] Electric drive systems are increasingly being used in modern vehicles, partly for reasons of sustainability and CO2 emission avoidance. Such drive systems contain one or more electric machines, e.g., synchronous or asynchronous machines, that are powered by a polyphase AC voltage. So-called two-level inverters (abbreviated as 2L inverters) are widely used to generate the AC voltage. In a two-level inverter, an AC voltage with two voltage levels is generated from the DC voltage of a DC voltage source.

[0012] Two-level inverters are more established than other inverter topologies, especially in the field of drive inverters for electric vehicles. Currently, two-level inverters primarily use IGBT switching devices. An example of such a two-level inverter is disclosed in the paper "Power Electronic Architectures for Electric Vehicles" by Hv Hoeck, published in "Emobility - Electrical Power Train" by IEEE in 2010.

[0013] In addition to the two-level inverter topologies mentioned above, there are also three-level or multilevel inverter topologies, which can generate three or multilevel voltage levels. Examples of multilevel inverter topologies are described, for example, in patent document US10903758B2 or patent document US2017 / 0185130A1.

[0014] The advantages of multiple voltage levels are fewer harmonics, slower voltage changes at the phase outputs, less electromagnetic radiation (EME), and, most importantly, the ability to handle higher voltages. For these reasons, such three-level or higher inverters are currently used primarily in high-voltage applications. Power engineering applications such as solar inverters or wind turbines are well-established areas of use for such three-level or multilevel inverter topologies. Higher voltages are not found in electric vehicles (e.g., voltages of 400 V). On the other hand, voltages of 1 kV or more are common in solar power generation, and in other renewable energy sources such as wind energy, voltages are significantly higher.

[0015] However, as described in the paper "Experimental Validation of Design Concepts for Future EV-Traction Inverters" by Andreas Bubert et al., 2018 IEEE Transportation Electrification Conference and Expo (ITEC), pp. 795-802, the general consensus is that the advantages of three-level or multilevel inverters described above are not sufficient to justify their use in electric drives of electric vehicles. For all these reasons, three-level or multilevel inverter topologies are not used in electric vehicles today. Summary of the Invention

[0016] The invention is based on the problem of increasing the efficiency of an electric drive system with a double rotor while at the same time making it easier and more cost-effective to manufacture.

[0017] According to the invention, this problem is solved by an electric drive system with the features of claim 1.

[0018] Therefore, there is provided an electric drive system for or in a motor vehicle, comprising at least one synchronous machine with a double rotor and distributed windings arranged in a stator core, said double rotor being made of a magnetic flux propagation material made of a solid material and said windings designed to be self-sustaining for torque support, and at least one three-level or multilevel inverter circuit coupled to said synchronous machine at a load output and designed to convert a DC voltage received on the supply side into an AC voltage capable of driving said synchronous machine via the load output, said inverter circuit having a controllable three-level or multilevel inverter.

[0019] The core idea of ​​the present invention is the combination of a specific electric synchronous machine, in which the stator has a distributed winding designed to be self-supporting for torque support and the double rotor is made of solid rotor material, i.e., a solid structure, with a three-level or multilevel inverter circuit.

[0020] The torsionally stiff windings offer the first opportunity to design the windings of synchronous machines with double rotors, particularly yokeless double rotor machines, as distributed windings with a correspondingly low upper magnetic field spectrum. Because the windings only generate low upper magnetic fields and the resulting eddy currents in the rotor, only in this embodiment can the rotor be manufactured from solid material. This significantly simplifies and makes rotor manufacturing significantly more cost-effective. Therefore, the electric drive system embodiments according to the present invention offer considerable technical and economic advantages due to the reduced material costs and complexity of the rotor.

[0021] However, when such machines are operated with a two-level inverter, as is common in prior art electric machines, the current harmonics induced by the inverter cause eddy currents in the solid rotor, resulting in additional losses. These harmonic losses are particularly relevant at low output torques and significantly reduce efficiency.

[0022] The use of a rotor made of solid-state magnetic flux-carrying material in combination with a three-level or multilevel inverter according to the present invention significantly reduces the harmonics that contribute to the input voltage, resulting in a loss reduction of 75% or more. Harmonic losses in prior art electric machines do not play a significant role, and therefore the additional cost of a three-level inverter cannot be justified.

[0023] The combination of features according to the invention is considered to be advantageous only in this particular case, since the underlying finding is that electric machines with double rotors made from solid materials have high losses in the rotors when fed from a conventional 2L inverter.

[0024] By design, losses in the electric machine cannot be reduced, or can only be reduced slightly. Reducing losses by increasing the frequency in 2L operation has little effect, but increases losses in the inverter, thus affecting overall efficiency.

[0025] The basic mechanism for reducing losses in the solid materials of a double rotor is based on the fact that the amplitude of the specific magnetic flux density in the solid materials of a double rotor that does not contribute to torque formation should be reduced. This component, defined by harmonics in the magnetic flux density, is approximately directly proportional to the square of its amplitude, which changes the THD-induced losses. Therefore, changing the inverter switching frequency leads to an indirect, proportional, linear change in losses, which is ineffective.

[0026] Reducing losses in solid materials reduces the overall losses of the electric machine and contributes significantly to its economical use. Thus, the resulting finding, which is part of the present invention, is that losses in an electric machine can be effectively reduced by an inverter circuit that reduces only the amplitude of harmonics in the magnetic flux density.

[0027] To achieve this, the following measures and aspects were considered in the design of the inverter and in the selection of its operating mode:

[0028] The function of a 2L inverter is replaced by that of a 3L inverter, reducing the harmonics in the inverter phase output. This reduces the harmonics in the flux density and stator current. There is no need to change the frequency for this.

[0029] Increasing the switching frequency in 2L operation also reduces losses, but this also significantly increases the inverter's switching losses and does not significantly improve overall efficiency, so increasing the switching frequency is not implemented. Although increasing the switching frequency may positively support loss optimization, it is not an essential aspect of the solution according to the present invention.

[0030] In contrast, the 3L inverter used provides three voltage levels (3L) and is preferably (but not necessarily) three phases. Three voltage levels and three phases allow for relatively greater cost efficiencies. However, the system can be expanded to any number of phases and any number of voltage levels, provided all phases are of the same design.

[0031] In contrast to known 2L inverters, when operating a 3L inverter according to the present invention, the power losses in the electric machine are significantly reduced due to the lower harmonics. The switching losses of the 3L inverter are also relatively reduced, but the transmission losses are increased.

[0032] In both electric machines and 3L inverters, the general loss mechanisms change with load. In 3L operation, mechanical losses are significantly reduced due to low harmonics. Harmonic losses dominate at low currents. At high currents, the dominant loss mechanisms change, with resistive conduction or copper losses dominating, and harmonic-induced losses tend to be secondary or relatively small. Switching losses in the inverter are reduced (by approximately 50%) in 3L inverters compared to 2L inverters. At low loads (currents), these switching losses dominate; at high currents, conduction losses dominate, making 2L operation more efficient. These findings led to the inventive concept of using a 3L inverter for low loads and a 2L inverter for high loads. The controllable three-level or multilevel inverter of the present invention makes this operation possible.

[0033] Overall, the advantages of 2L operation can be combined with those of 3L operation, particularly in the case of electric machines with double rotor motors, which can significantly increase the overall efficiency of the electric drive system compared to known electric drive systems.

[0034] Another finding underlying the present invention is that the windings of a radial flux double-rotor machine can be designed to transmit force for torque support. Therefore, a fundamental aspect of the present invention is to design the windings arranged on the stator core to be self-supporting for torque support.

[0035] A free-standing winding design is understood to mean that the windings have sufficient rigidity and strength to support the drive torque against torsion about the mechanical axis. The free-standing windings are embedded in a magnetically soft stator core specifically for magnetic flux propagation. This has the particular advantage that the stator core itself does not require inherent torsional rigidity against the mechanical axis, nor is any additional support structure required to secure the stator core. Instead, the torque is supported entirely through the windings specifically.

[0036] The windings are so-called distributed windings. This means that the forward and return conductors of the winding strands are distributed tangentially around the circumference, with the forward and return conductors of one strand tangentially located between the conductors of another strand. This creates a nested arrangement that requires crossings of the conductors of different strands, especially in the winding head area. In particular, distributed windings result in a winding head without crossings, in contrast to so-called toothed coil windings, in which the forward and return conductors of a strand are located in adjacent slots.

[0037] Therefore, in the field of radial flux double rotor machines, providing the distributed winding with a torque support function in addition to current carrying provides a previously unknown or technically unrealizable functional integration. For example, for this purpose, the winding may be mechanically fixed to the outside of the stator core at one axial end.

[0038] To manufacture such windings, it has been proposed to manufacture them integrally with the existing stator core. To this end, the individual bars of the winding are inserted axially through the radially inner and outer stator slots in the direction of the spiral of the stator slots and connected at both conductor ends. This is preferably achieved by material joining using welding or soldering. This allows the winding to be connected to the stator core by fitting.

[0039] The selected pitch angle (also known as the set angle) of the stator slots or the spirals described therein ensures that the connections of the inserted conductor bars result in the formation of nested conductor loops, resulting in a distributed winding. The angle of the conductor loops, swept relative to the central axis, encircles one magnetic pole of each rotor. This allows for a very simple manufacture of the stator, despite its functional integration, using very few components and relatively simple conventional connection techniques, and therefore very few manufacturing steps.

[0040] The stator designed in this way, together with the inner and outer rotors made of solid materials, completes the synchronous machine of the electric drive system according to the present invention. For example, it can be a permanently excited rotor with surface and / or embedded magnets, a squirrel-cage rotor, or an electrically excited rotor. Hybrid variations with different rotor variations for the inner and outer rotors are also possible. This design is particularly advantageous when the rotor is made of a soft magnetic solid material and has permanent magnets attached to its surface. The small upper magnetic field spectrum of the winding variations described here and the distance between the air gap and the solid material ensured by the magnets prevent unacceptably large losses due to eddy currents in the rotor. In this embodiment, a relatively high efficiency can be achieved, and the rotor can still be manufactured at very low cost.

[0041] The synchronous machine is, for example, integrated into the axle of a motor vehicle and is arranged to drive the drive wheels, in particular the synchronous machine can be coupled to the drive wheels without a transmission.

[0042] Also disclosed according to one aspect is an electric drive system according to the invention, particularly having an axle for a motor vehicle, in which a synchronous machine having a double rotor is coupled to the drive wheels without a transmission.

[0043] Also disclosed according to one aspect is a motor vehicle having such an electric drive system.

[0044] Advantageous embodiments and further developments result from the other subclaims and the description with reference to the drawing figures.

[0045] According to an advantageous embodiment, the synchronous machine is designed as a radial flux double rotor machine, which allows the mass of the radial flux double rotor machine to be reduced and the torque density to be increased due to functional integration.

[0046] According to a particularly preferred embodiment, the synchronous machine is designed for a wheel hub drive, in particular as a wheel hub motor for an electric vehicle. A wheel hub motor is an electric machine that is attached directly to the wheel, in particular to the hub of a vehicle, and simultaneously supports the wheel hub. Part of the hub motor transmits the generated torque directly to the driven wheel, causing it to rotate. The main advantage of such an electric wheel hub motor compared to drive concepts with a central motor is that a classic driveline with its required components (transmission, cardan shaft, differential gear, drive shaft, etc.) is no longer necessary. These transmission losses are also eliminated, which increases the efficiency of the entire drive system. Efficient regeneration, i.e., the recovery of electrical energy when the vehicle brakes, can also be implemented in an electric wheel hub motor.

[0047] According to a particularly preferred embodiment, this is a wheel hub drive with a radial flux double rotor machine. The design of the present invention, which reduces the mass of the radial flux double rotor machine and increases its torque density, allows for a reduction in the unsprung mass of the axle, which is particularly advantageous for wheel hub motors. Furthermore, according to the present invention, a relatively large diameter and a relatively short axial length can be realized, which is particularly advantageous in terms of torque support and installation space within the wheel. Meanwhile, according to the present invention, despite the extremely compact design, very high torques are possible, particularly sufficient to directly drive the vehicle wheels without a transmission. Thus, according to a particularly advantageous embodiment, transmission losses are avoided, further weight savings are achieved, and particularly high efficiency benefits are achieved. Furthermore, this high torque can already reach the four-digit range, particularly above 5000 Nm, in an installation size within the dimensions of a conventional automobile wheel, reaching the grip limit of conventional road tires and even replacing the rear wheel brake with a wheel hub motor. Thus, special synergistic effects are possible in the application as a wheel hub motor.

[0048] According to one embodiment, the windings protrude beyond the stator core at at least one axial end. Furthermore, a support device is provided that is axially offset relative to the stator core and is designed to engage with the windings at at least one axial end for torque support. In this way, the free-standing windings engage with the support device for torque support that is axially offset relative to the stator core.

[0049] According to one embodiment, the synchronous machine has a mechanically fixed base. The support device is engaged by a snap-fit ​​with at least one axial end of the torque-supporting winding and is supported on the base. In a suitable manner, the support device is rigidly connected to the base as a fixed part of the synchronous machine. One possible embodiment provides for this purpose recesses, e.g., through-holes, for fastening means, such as screws. However, it is of course also conceivable to use snap-fit ​​connecting means and / or material joints as an alternative or additional means.

[0050] According to one embodiment, the double rotor has a first rotor made of solid material arranged radially inside the stator core and a second rotor made of solid material arranged radially outside the stator core, and the rotors are preferably rigidly connected to each other, for example by pressing, riveting or screwing.

[0051] According to one embodiment, the magnetic flux carrying material of the double rotor or the first and second rotors consists of iron or an iron alloy, which advantageously optimizes the magnetic flux.

[0052] Similarly, according to a particularly preferred embodiment, the synchronous machine is a three-phase synchronous machine. In this case, the inverter circuit is preferably designed as at least a three-phase inverter. It is also a finding of the present invention that synchronous machines utilizing a three-phase or polyphase inverter topology exhibit substantially improved overall drive system efficiency.

[0053] According to one embodiment, the inverter circuit comprises an operating mode setting device designed to change the inverter from three-level or multi-level operation to two-level operation or vice versa depending on the overall efficiency of the electric drive system, the overall efficiency being a function of the detected phase currents of the synchronous machine and at least one other parameter and / or characteristic that influences the overall efficiency.

[0054] According to another embodiment, the inverter circuit comprises operating mode setting means designed to change the inverter from three-level or multi-level operation to two-level operation or vice versa depending on the overall efficiency of the electric drive system, the overall efficiency being an sole function of the detected phase currents of the synchronous machine or a function of at least one other characteristic of the synchronous machine that influences the overall efficiency.

[0055] According to one embodiment, the operating mode setting device includes an evaluation device designed to optimize the overall efficiency based on the phase currents or at least one other characteristic. According to one aspect of the present invention, this includes a special inverter circuit associated with the overall drive system adaptation, thereby enabling an increase in overall benefits without the associated increase in costs. For this purpose, it is proposed to use a novel controllable three-level or multilevel inverter capable of three-level or multilevel operation (hereinafter referred to as 3L operation) and two-level operation (hereinafter referred to as 2L operation). The operating mode setting device, specially provided for this purpose, sets the respective operating mode by appropriately controlling the inverter's power switches. The operating mode is set depending on the overall efficiency of the entire drive system, and is therefore not simply based on, for example, the synchronous machine and / or inverter used. As with other inverters, the overall efficiency is determined by taking into account not only the detected phase currents of the synchronous machine but also other parameters and / or characteristics of the synchronous machine that affect the overall efficiency. In known drive systems, the latter are not taken into account in the efficiency evaluation and analysis. Therefore, according to the present invention, an overall efficiency analysis is performed here.

[0056] In this case, one concept of the present invention is to reduce losses, especially at low loads, by operating the inverter at 3L. In this case, inverter losses at all operating points are at most barely increased or even reduced. Therefore, the overall efficiency of the drive system, i.e., inverter and synchronous machine, is significantly improved, especially when used in electric drive vehicles.

[0057] According to a preferred embodiment of the present invention, the inverter circuit includes an operating mode setting device. It is essential that the operating mode setting device does not necessarily switch abruptly from 2L operation to 3L operation or vice versa. Rather, such switching can be performed sequentially, for example, by transitioning from the inner power switch to the outer power switch. This transition can be performed, for example, taking into account the average current values ​​of the different power switches and taking into account the operating time or the time each power switch is turned on. Additionally or alternatively, the power switches can be switched in a predetermined sequence and / or slowly.

[0058] For example, the operating mode setting device with the evaluation device, control device and / or measuring device can be designed as a programmable control device, such as a microprocessor or microcontroller, although it would also be feasible to provide logic circuits such as FPGAs, PLDs, etc. for this function.

[0059] According to another advantageous development, the operating mode setting device has an evaluation device that is designed to optimize the overall efficiency of the electric drive system based on the phase currents and based on at least one other parameter and / or at least one characteristic of the electric drive system.

[0060] Typically, but not necessarily, the overall efficiency is calculated numerically by an evaluation circuit. Additionally or alternatively, the overall efficiency may be determined based on a preset family of characteristics, for example, mapped to a lookup table. The overall efficiency may be calculated or determined during operation or, for example, in advance. Preferably, in so-called offline operation, the optimal, i.e., most efficient, operating strategy is calculated, for example, numerically, before the electric drive system is put into operation. This can be achieved with relatively few computer resources and is particularly preferred when a large number of parameters are considered in the numerical prediction of the optimal overall efficiency. Furthermore, offline operation allows more time for calculation. However, as an alternative, a highly dynamic determination of the respective operating mode (2L operation or 3L operation) is also conceivable and possible in so-called real-time operation, for example, via a lookup table. This is particularly advantageous and possible when the number of parameters used in the overall efficiency calculation is small. For example, for these purposes, an artificial network trained based on previous parameter values, characteristic curves, etc., can be used.

[0061] According to a preferred embodiment, the evaluation device includes an optimization module designed to first determine the overall efficiency. Alternatively or additionally, the overall efficiency can then be optimized via an optimization function, taking into account the phase currents and at least one other parameter and / or characteristic. The optimization of the overall efficiency can be performed analytically and / or via, for example, a suitable pre-generated look-up table.

[0062] As other parameters, at least one of the following parameters is provided: - inverter circuit temperature, - synchronous machine temperature, - inverter intermediate circuit voltage, - rotor speed or rotor revolutions, - synchronous machine torque, - modulation level, - Phase voltage or phase current. Of course, other parameters are also possible.

[0063] The operating mode used in each case (e.g. 2L or 3L operation) is a characteristic of the synchronous machine that affects, for example, the overall efficiency. Another characteristic can be found in the specific configuration of the rotor of the synchronous machine, for example, that the rotor is a double rotor and / or that the double rotor is made of a solid flux-carrying material.

[0064] According to a preferred exemplary embodiment, the operating mode setting device comprises at least one measuring device.

[0065] The first measurement device has at least one sensor input, via which it can be coupled to the synchronous machine. The first measurement device is designed to detect phase currents, temperature, rotor speed, and / or other measurable parameters. For example, the temperature of the synchronous machine or its rotor can be detected via a corresponding thermocouple. Alternatively, the temperature-dependent change in electrical resistance of certain conductors and semiconductors or, for example, certain semiconductor circuits, can be used to generate a voltage proportional to absolute temperature (keyword: bandgap reference). The torque of a synchronous machine cannot be measured directly, but can be calculated, particularly by measuring the phase currents. The rotor rotation speed, and therefore the rotor speed, can be determined in various ways, for example, using Hall sensors or incremental encoders attached to the rotor.

[0066] The second measuring device is arranged and designed to detect the temperature and / or intermediate circuit voltage of the inverter. The temperature measurement can be performed in a similar manner as described above for the first measuring device.

[0067] According to a preferred exemplary embodiment, the inverter includes a t-type neutral point clamped (TNPC) inverter architecture.

[0068] These inverters offer various advantages over multilevel active neutral-point clamped (ANPC) inverter topologies. In contrast to the ANPC topology, conduction losses are lower because up to three switches conduct in series instead of four. Because the output voltage waveform is the same, switching losses are similarly low. However, at high switching frequencies (e.g., greater than 10 kHz), the total chip area required for TNPC topologies is smaller than that of two-level topologies. Similar to ANPC, hybrid inverter topologies can also be constructed for TNPC to further improve efficiency and optimize manufacturing costs. For example, different switch technologies can be used for this purpose in the zero-voltage or mid-bridge branches. In particular, losses can be significantly reduced by using gallium nitride (GaN) in TNPC inverters composed solely of insulated-gate bipolar transistors (IGBTs). Hybrid TNPC inverter topologies can also be used for motor control in electric vehicles, but are rarely seen in practice. It is particularly advantageous to design a three-level inverter as a T-type converter, with the center switch's current-carrying capacity significantly smaller than the outer switches. In the low output torque region, the converter operates at 3 L, and in the high output torque region, it operates at 2 L. The advantage of this embodiment is that harmonic losses can be avoided in the low output torque region where they are particularly important.

[0069] TNPC-based 3L inverters can be operated in two operating modes to increase system efficiency. In the case of a 3L TNPC inverter, the zero potential (middle) bridge branch can be switched off to operate in 2L operation and switched on to change to 3L operation. Switching between the two operating modes is done to increase system efficiency. To do so, the control and regulation logic measures the load and switches between 2L and 3L operation using pre-determined optimization characteristics.

[0070] Additionally or alternatively, TNPC-based 3L inverters may be designed asymmetrically to reduce inverter costs. The asymmetry refers to the current-carrying capacity of the zero-potential (middle) bridge branch being lower than the current-carrying capacity of the outer bridge branches. This is because the zero-potential bridge branch is not used at high loads to optimize overall efficiency. The outer bridge branch is designed for peak currents, while the zero-potential bridge branch is designed for small or continuous currents.

[0071] According to one embodiment of the present invention, an inverter comprises a first driver stage and at least one second driver stage designed to provide a smaller output load current to a load output than the output load current provided by the first driver stage.

[0072] Preferably, the operating mode setting device is designed to control the inverter to activate the first and second driver stages in three-level or multi-level operation and to deactivate at least one driver stage, preferably the inner second driver stage, in two-level operation depending on the overall efficiency.

[0073] Typically, but not necessarily, the first driver stage includes at least one bridge circuit, particularly a half-bridge circuit, whose center tap forms the inverter circuit's output load terminal. Each bridge circuit includes at least one first (semiconductor) power switch connected to a first power supply terminal (e.g., a positive power supply potential) and designed to provide a first voltage level to the load output. Each bridge circuit also includes at least one second (semiconductor) power switch connected to a second power supply terminal (e.g., a negative power supply or reference potential) and designed to provide a second voltage level to the load output. Semiconductor-based power switches can be fabricated from a variety of selectable semiconductor materials. Commonly used materials are Si (silicon) for IGBTs and MOSFETs, SiC (silicon carbide) for MOSFETs, and GaN (gallium nitride) for MOSFETs.

[0074] Typically, but not necessarily, the second driver stage includes at least one third power switch having its load path connected in series between the intermediate circuit and the center tap of the first driver circuit, the power switch of the second driver stage being designed to provide a third voltage level to the load output that is intermediate between the first and second voltage levels.

[0075] In the case of a preferred, so-called homogeneous inverter topology, all power switches of the inverter, i.e., the power switches of the first and / or second driver stages, are designed as semiconductor switches of the same switch type and / or the same semiconductor technology. Switch types include, for example, bipolar transistors, field-effect transistors (MOSFETs, JFETs, etc.), thyristors, IGBTs, etc. Semiconductor technology refers to the semiconductor technology on which the power switches are manufactured, such as Si, SiC, GaAs, or GaN technology.

[0076] In a first preferred variant of the homogeneous inverter topology, the semiconductor switches are designed as GaN power switches, e.g., GaN MOSFETs. In a particularly preferred second variant, the semiconductor switches are designed as SiC power switches, in particular SiC MOSFETs. Furthermore, IGBT-based power switches, e.g., silicon-based IGBTs with Si or SiC diodes, are also feasible.

[0077] In a particularly preferred so-called hybrid inverter topology, at least two different switch types and / or at least two different semiconductor technologies are provided for the inverter's semiconductor switches, i.e., for the semiconductor switches of the first driver stage and / or the semiconductor switches of the second driver stage. In a hybrid inverter topology, not all power switches in the inverter are made of the same semiconductor material. In particular, the power switches of the zero-potential bridge branch, i.e., the power switches of the second driver stage, use a different technology (different switch type) than the external switches of the first driver stage. This reduces switching and conduction losses and improves efficiency. Furthermore, cost benefits are also achieved. It is particularly recommended to optimize the power switches of the zero-potential bridge branch (second driver stage) to minimize switching and reverse recovery losses. This is because the zero-potential bridge branch (second driver stage) operates at low currents, and the low reverse recovery losses also reduce the switching losses of the external switches. A hybrid design is particularly recommended for asymmetric inverters. The lower the current-carrying capacity of the zero-potential bridge branch (second driver stage), the lower the additional cost of switching the loss-optimized switches.

[0078] In a first particularly preferred variant, the semiconductor switches of the first driver stage are designed as IGBTs (Si or SiC) with freewheeling diodes, while the semiconductor switches of the second driver stage can preferably be designed as SiC power switches, in particular SiC MOSFETs.

[0079] In a second variant, which is also preferred, the semiconductor switches of the first driver stage are designed as SiC MOSFETs, while the semiconductor switches of the second driver stage can be designed as GaN-based MOSFETs.

[0080] In a third preferred variant, the semiconductor switches of the first driver stage are designed as IGBTs with freewheeling diodes, while the semiconductor switches of the second driver stage can be designed as GaN power switches, in particular GaN MOSFETs.

[0081] In a particularly preferred embodiment, the rotor's magnetic flux-carrying material is made of iron or an iron alloy. Rotating magnetic field machines, preferably synchronous machines with double rotors, can be designed so that the magnetic flux-carrying material in the rotor is solid. This is because, in an idealized synchronous machine, there is no periodic relative motion between the direction vector of the rotating magnetic field generated by the stator windings and the double rotor. Therefore, the magnetic flux density at the operating point is constant, and no iron losses occur in the material. In such permanent magnet machines, where the magnets are attached to the rotor surface, the resulting distance between the inductor grooves and the magnetic flux-carrying material allows the use of solid materials without increasing losses.

[0082] According to a similarly particularly preferred exemplary embodiment, the synchronous machine comprises a stator with an inductor that is designed to propagate magnetic flux primarily in the radial direction and in particular to avoid tangential magnetic flux propagation. The stator is therefore of a so-called "yokeless" design, which in particular avoids circumferential magnetic flux propagation. This eliminates the need for a magnetic return path within the stator, thereby reducing weight and iron losses.

[0083] According to one embodiment, the inductor of the stator has a radial yoke thickness of less than 30%, preferably less than 20%, particularly preferably less than 10% of the total radial thickness of the inductor. In so-called "yokeless" designs, a mechanical connection of the inductor teeth is provided in this way, but this is not electromagnetically necessary and there is no functionally relevant magnetic flux. The term "yokeless" therefore refers to the electromagnetic design of the inductor.

[0084] According to one embodiment, the windings are designed to be torsionally stiff so that torques acting on the stator core during operation of the radial flux double-rotor machine can be supported particularly completely via the torsionally stiff windings on the support members, which makes it possible to advantageously dispense with any other type of force support device, particularly for the stator core.

[0085] According to one embodiment, the stator core is designed to propagate magnetic flux primarily in the radial direction. This is a so-called "yokeless" design of the stator core, which specifically avoids circumferential or tangential magnetic flux propagation. Since no magnetic return path is required within the stator core, weight and iron losses are reduced.

[0086] According to one embodiment, the stator core has a radial yoke thickness of less than 30%, preferably less than 20%, and particularly preferably less than 10% of the total radial thickness of the stator core. In so-called "yokeless" designs, the mechanical connection of the stator teeth is achieved in this way, but this is not electromagnetically necessary and there is no functionally relevant magnetic flux. The term "yokeless" therefore particularly relates to the magnetic flux propagation in the stator core.

[0087] According to one embodiment, the winding is formed from conductor bars connected to one another, particularly in a rod-like manner. In particular, the conductor bars can be material-joined, for example, by welding or soldering. However, other connection techniques are also possible. Preferably, two conductor bars are connected at each end, and all conductor bars together form a bar structure. The bar structure formed by the conductor bars is advantageously designed to have torsional rigidity and to transmit torque around the central axis of the stator. Furthermore, the conductor bars are designed to be thick enough for power transmission. For example, in the case of a wheel hub motor, the thickness of the conductor bars can be in the range of several millimeters. In particular, square bars with sides of several millimeters can be used.

[0088] According to one embodiment, the winding has a radially inner layer of conductor bars arranged helically and a radially outer layer of conductor bars arranged helically in the opposite direction. In this way, the winding forms a bar structure with high torsional rigidity. The conductor bars of the inner layer and the outer layer each form a spiral with an opposite winding direction or pitch. The angle of the spiral between the start and end of the conductor bars, which are swept relative to the central axis of the stator, is specifically designed so that one conductor loop is formed for each rotor pole of a radial flux double-rotor machine. Therefore, the sweep angle can be calculated from the quotient of the angle of one revolution (2π or 360°) and twice the number of pole pairs p.

[0089] According to one embodiment, the radially inner and outer layers of the winding each have the thickness of a single conductor bar. That is, each phase of the winding is formed with a cross section of a single conductor bar. This winding design according to the present invention is made possible in particular by the special design of the radial flux double-rotor machine, whose magnetic symmetry prevents current displacement to the surface of the conductor. In this way, relatively thick conductor cross sections are possible while still achieving a relatively uniform current distribution across the cross section. For example, the thickness of the conductor bars can be in the range of several millimeters. In particular, the bars can have a square cross section with a side length of several millimeters, for example, in the range of 2 mm to 6 mm, in particular, in the range of 3 mm to 5 mm. Other cross-sectional shapes are also possible.

[0090] According to one embodiment, each conductor bar is twisted along a helical path so that the cross-section of the conductor bar is the same at every point on the conductor relative to the radial axis of the cross-section. In particular, this involves twisting the conductor bars, especially non-circular conductor bars, around the central axis of the stator or machine. Depending on the helical path, the conductor bars can also be bent. The inner and outer layers are alternately arranged with each other, i.e., rotated, twisted, and possibly bent in opposite directions. In this way, the conductor bar arrangement is ideally aligned from a mechanical standpoint at each point of the stator core for force transmission with the stator core, and each conductor bar is uniformly loaded along its length. As a result, in the bar structure, the conductor bars advantageously absorb primarily tensile and compressive stresses when subjected to tangential forces. Load peaks and deformations of the conductor bars are thus avoided. In particular, mechanical stresses can be significantly reduced compared to designs with straight conductor bars parallel to the axis.

[0091] According to one embodiment, the conductor bars of the radially inner and outer layers of the windings belonging to the same phase are connected to each other at their ends, in particular via radially arranged conductor bar pieces and / or by material joints. In addition to the conductor loops, when the axially accessible winding ends are fixed, a torsionally rigid bar structure is also created, so that high torques can be absorbed by the windings without causing unacceptably large deformations and / or stress states. In this way, a self-supporting design of the windings is made possible solely by the winding material, e.g., copper, without any additional support means or elements.

[0092] According to one embodiment, the stator core includes a laminated stator core having spiral stator slots corresponding to the winding paths, with a single conductor bar disposed in each stator slot of the laminated stator core. The windings or free-standing bar structures formed therewith are embedded in the laminated stator core in this manner. Like the conductor bars of the windings, the stator slots also change tangential position depending on their axial position, thereby forming a spiral shape. The direction of change in position follows the conductor bar. That is, the centerlines of the radially outer slots and the radially inner slots also describe spirals with opposite winding directions.

[0093] In other embodiments, other manufacturing methods known to those skilled in the art for producing a stator core shape according to the present invention in which the radially inner and outer stator slots extend in opposite helical directions are also contemplated, in particular additional manufacturing methods such as sintering processes.

[0094] According to one embodiment, only a single conductor bar is arranged in each stator slot of the laminated stator core. As already explained in connection with the windings, the conductor bars of the inner and outer stator slots are twisted around the central axis of the machine so that the ends of the conductor bars of the inner and outer layers are guided towards each other. At their ends, the conductor bars are electrically connected to each other, in particular via radially arranged conductor bar segments and / or by material joining, for example by welding or soldering.

[0095] According to one embodiment, the conductor-connected conductor bars of the inner and outer layers together form undulating winding strands. The winding strands can be interconnected by suitable interconnection means known to those skilled in the art to form a rotating field generating winding with a desired or adjustable number of strands. The number of strand turns required to maintain a voltage is determined directly from the quotient of the product of the number of slots in the molecule, the number of strands, and the number of parallel branches in the molecule. Advantageously, the number of parallel branches is selected to be 1. This provides the simplest winding interconnection.

[0096] According to one embodiment, the stator laminations of the stacked stator core are each formed to the same shape with recesses for forming the stator slots. The spiral path of the stator slots is provided by stacking the stator laminations in a twisted arrangement relative to one another. In this way, the same punching die can be used for all parallel-arranged or stacked stator laminations, making the stator laminations very economical to manufacture. Therefore, two adjacent stator laminations are slightly twisted relative to one another by a predetermined angle around the central axis so that the recesses are arranged to overlap each other in accordance with the spiral.

[0097] According to an advantageous embodiment, the laminated stator core includes an inner subpackage having a radially inner stator slot and an outer subpackage having a radially outer stator slot. The stator laminations of the inner subpackage each have the same shape, and the stator laminations of the outer subpackage each have the same shape. The stator laminations of the inner subpackage and the stator laminations of the outer subpackage are laminated while twisted in opposite directions. In this way, the opposite spiraling of the stator slots can be achieved with minimal manufacturing effort. Nevertheless, a very economical manufacturing method is still possible, since the same punching die can be used for all parallel or stacked stator laminations of the inner subpackage and for all parallel or stacked stator laminations of the outer subpackage. Thus, two adjacent stator laminations of the inner subpackage are twisted slightly relative to each other in a first direction by a predetermined angle about the central axis, and two adjacent stator laminations of the outer subpackage are twisted slightly relative to each other in an opposite second direction by a predetermined angle about the central axis. In this way, the recesses in the stator thin plates of the inner subpackage and the outer subpackage correspond to spirals in opposite directions and are arranged overlapping and facing each other.

[0098] According to another embodiment, the stator laminations are formed with different recesses for forming the stator slots. The spiral path of the stator slots is provided by different distances between the recesses in the individual stator laminations. In this respect, a corresponding stator lamination shape is produced individually for each position of the stator lamination in the stack, so that the individual shapes can also be repeated within the stack. This can be achieved, for example, by a photo-cutting process, in particular a laser photo-cutting process, which is more flexible in terms of shape than a stamping process. It is also possible to use flexible stamping dies with variable shapes or, in the case of very large production volumes, several individual stamping dies for different stator laminations.

[0099] In another development, the recesses for the radially inner and outer stator slots are each integrally formed in a common stator lamella, so that the opposing spiral paths of the radially inner and outer stator slots are provided by the continuous displacement of the inner and outer stator slots relative to each other from stator lamella to stator lamella. Again, for each position of the stator lamella in the lamination, an individually matching stator lamella shape is produced, so that the individual shapes can be repeated within the lamination. Again, flexible cutting processes, such as laser cutting, are used for production. This integrated production of the inner and outer recesses reduces the number of parts.

[0100] According to one embodiment, the stator laminations have straight, particularly punched, edges. The width of the recesses provided for the stator slots is greater than the width of the conductor bars by an amount determined by the pitch of the spiral shape of the stator slots and the thickness of the stator laminations. Therefore, the reduced gap width or continuous width of the stator slots due to the offset between the recesses in the stator laminations essentially corresponds to the width of the conductor bars. In practice, the continuous gap width of the stator slots is slightly greater than the width of the conductor bars to provide the necessary clearance fit for their insertion. In this way, the ends of the stator slots form a step shape with a difference in thickness, against which the conductor bars are uniformly supported. In this way, torque support is uniform throughout the thickness of the laminated stator core or throughout the length of the conductor bars housed in the laminated stator core.

[0101] According to one embodiment, the respective sweep angles of the stator slots are smaller than the respective sweep angles of the conductor bars. The respective sweep angles refer to the rotation angles around the central axis of the stator. The difference in sweep angles is due to the fact that the conductor bars protrude axially beyond the stator core and are therefore longer than the stator slots. The helical path is also continuous, resulting in a larger sweep angle. This difference is provided to ensure sufficient accessibility of the winding ends for joining, in particular welding, the ends of the conductor bars after insertion into the stator slots. Furthermore, this allows for axially offset engagement of the windings with the support device or its support members.

[0102] From the quotient of the sweep angles, i.e. the ratio of the angle swept by each stator slot to the angle swept by each conductor bar, it is possible to define the so-called pole coverage of the laminated stator core.

[0103] According to one embodiment, the ratio of the angle swept by each stator slot to the angle swept by each conductor bar is in the range of 0.6 to 0.8, in particular 0.6 to 0.75, preferably 0.6 to 0.7. This ratio (pole coverage) provides an optimum between current heat losses and torque utilization in this range.

[0104] According to one embodiment, the support device comprises a support element that corresponds to the helical arrangement of the conductor bars and is provided with support grooves that engage with the conductor bars, thus providing a fitting embedding of the conductor bars in the support element for torque support at the axial ends, preferably engaging all the conductor bars so that torque support is transmitted homogeneously or uniformly over the entire bar system of the winding.

[0105] To transmit torque, the support member can be connected to the mechanically fixed base of the radial flux double rotor machine. One possible embodiment provides through holes for non-interlocking fasteners such as screws, but interlocking fasteners or material joints would also be possible.

[0106] According to one embodiment, the support grooves at least partially follow the helical path of the twisted conductor bars. In particular, the support grooves follow the same twisted path as the conductor bars. For example, the support member may be substantially annular and have radially aligned recesses on its inner and / or outer periphery that correspond to the path of the conductor bars.

[0107] According to one embodiment, the support device comprises a radially inner support member for engaging with the radially inner layer of conductor bars and a radially outer support member for engaging with the radially outer layer of conductor bars. In this embodiment, the support members can be annular, with the inner support member having grooves or teeth on its outer peripheral surface corresponding to the paths of the inner layer of conductor bars for matingly receiving the radially inner conductor bar, and the outer support member having grooves or teeth on its inner peripheral surface corresponding to the paths of the outer layer of conductor bars for matingly receiving the radially outer conductor bar. In particular, the grooves or teeth follow the respective helical paths. The inner or outer peripheral arrangement means that the recessed grooves are easily accessible for machining, which simplifies the manufacture of the support members.

[0108] According to one embodiment of the radial flux double rotor machine, the support members are fixed to the base, thereby conducting torque to the stationary parts of the electric machine. For this purpose, the support members can be fixed separately to the base, e.g., the housing, of the machine. Alternatively or additionally, the inner and outer support members can be fixed to each other.

[0109] According to one embodiment of the stator, the support device comprises a thermally conductive material, in particular a metal, preferably an aluminum alloy. In particular, both support members can comprise such a material. In this way, in addition to high mechanical strength, heat dissipation from the windings via the support members is also possible.

[0110] In one embodiment of a corresponding radial-flux double-rotor machine with a support device made of a thermally conductive material, the base further includes a heat sink designed to absorb heat dissipated from the stator, particularly from the windings, through the support device. As a result, the support device has high mechanical strength while simultaneously ensuring a good thermal connection between the windings and the heat sink. For example, the machine housing can function as the heat sink. Alternatively or additionally, the support device, preferably the inner and outer support members, can be in thermal contact with an actively cooled heat sink of the machine. In this way, current heat losses occurring in the windings or conductor bars can be effectively dissipated.

[0111] According to one embodiment of the radial flux double rotor machine, both the first and second rotors are provided with a predetermined number of pole pairs. The angle swept by each conductor bar is designed to form a conductor loop for each rotor pole. Therefore, the swept angle can be calculated from the quotient of the angle of one revolution (2π or 360°) and twice the number of pole pairs p.

[0112] The above-described embodiments and developments can be combined with one another as desired, if useful. Further possible embodiments, other developments and implementations of the invention also include combinations not explicitly mentioned of the features of the invention described above or below with respect to the illustrated embodiments. In particular, in this regard, those skilled in the art will be able to add individual aspects as improvements or additions to the respective basic forms of the invention. [Brief explanation of the drawings]

[0113] The invention will now be explained in more detail with reference to embodiments illustrated in the schematic diagrams of the drawings. [Figure 1] 1 is a block diagram illustrating an electric drive system according to the present invention. [Figure 2] FIG. 1 is a block diagram of an electric drive system according to an embodiment. [Figure 3]2 is a schematic cross-sectional view of an example of an electric machine of the electric drive system according to the present invention of FIG. 1; [Figure 4] 2 is a block diagram of a three-level or multilevel inverter circuit of the electric drive system of FIG. 1 according to the present invention. [Figure 5] 1 is a circuit diagram of a particularly preferred exemplary embodiment of an inverter circuit according to the present invention; [Figure 6] 1 is a flow diagram of a method for operating an electric drive system according to the present invention; [Figure 7] FIG. 2 is a schematic vertical cross-sectional view of a stator. [Figure 8] FIG. 1 is a schematic longitudinal cross-sectional view of a radial flux double rotor machine. [Figure 9] FIG. 2 is an exploded perspective view of a stator according to an embodiment. [Figure 10] FIG. 1 is an exploded perspective view of a radial flux double rotor machine according to an embodiment. [Figure 11] FIG. 10 is an exploded perspective view of a radial flux double-rotor machine according to another embodiment. [Figure 12] FIG. 12 is a perspective view of the radial flux double rotor machine of FIG. 11 in an assembled state. [Figure 13] FIG. 10 is a vertical cross-sectional perspective view of a radial flux double-rotor machine according to another embodiment. [Figure 14] FIG. 2 is an exploded perspective view of a laminated stator core. [Figure 15] FIG. 2 is a schematic vertical cross-sectional view of a stator slot. [Figure 16] FIG. [Figure 17] FIG. [Figure 18] FIG. 10 is a perspective view of an FEM simulation of a state in which a load is applied to the winding. [Figure 19] FIG. 10 is a perspective view of an FEM simulation of a comparative winding in which the conductor bars are designed to be linear under load. [Figure 20] 10 is a flowchart of a method for manufacturing a stator.

[0114] The accompanying drawings are intended to provide a further understanding of embodiments of the present invention. These drawings illustrate embodiments and, together with the specification, serve to explain the principles and concepts of the present invention. Other embodiments and many of the stated advantages will become apparent upon review of the drawings. Elements of the drawings are not necessarily shown to scale relative to each other.

[0115] In the drawing figures, similar, functionally identical, and operating in the same manner elements, features and components are respectively designated with the same reference numerals unless otherwise stated. DETAILED DESCRIPTION OF THE INVENTION

[0116] FIG. 1 is a block diagram of an electric drive system 10 for a vehicle according to the present invention. The electric drive system, designated herein by the reference numeral 10, is preferably (but not necessarily) intended for use in a motor vehicle.

[0117] The drive system 10 includes at least one polyphase electric synchronous machine (synchronous machine) 11 and an inverter circuit 12. The synchronous machine 11 is symbolically shown in cross section in the block diagram and is connected at its input side to an inverter circuit 12 which drives the synchronous machine 11.

[0118] The synchronous machine 11 is designed as a double rotor machine and therefore includes two rotors 21, 22. Further provided is a stator including a stator core 2 and a distributed winding 3 arranged within the stator core 2 and designed to be self-supporting for torque support. The double rotor, or rotors 21 and 22, are made of a magnetic flux transmitting material made of a solid material.

[0119] According to the present invention, the inverter circuit 12 is designed as a three-level or multi-level inverter circuit 12. The inverter circuit 12 has at least one inverter 13.

[0120] The inverter 13 is coupled to the electric machine 11 via its load output 15 and to a supply voltage source 18 via power supply terminals 16, 17. The inverter 13 is thus designed to convert a direct current voltage VDC received on the supply side into an alternating current voltage VAC. The inverter 13 is designed as a multi-phase inverter 13, the number of phases of which usually corresponds to the number of phases of the electric machine 11. The electric machine 11 is driven by the phase currents supplied by the inverter 13 at the load output 15.

[0121] Preferably, the synchronous machine is a yokeless double-rotor machine. The torsionally stiff windings are designed as distributed windings with a correspondingly low upper magnetic field spectrum. This design allows the rotor to be manufactured from solid material, since the windings generate only a low upper magnetic field and the resulting eddy currents in the rotor.

[0122] The three-level or multilevel inverter circuit 12 reduces induced current harmonics that, in conventional two-level inverters, cause eddy currents and additional losses in rotors made of solid materials. By operating the three-level or multilevel inverter circuit 12, the input voltage harmonics can be significantly reduced, resulting in a loss reduction of 75% or more.

[0123] FIG. 2 is a block diagram illustrating an electric drive system 10 according to one embodiment.

[0124] In the illustrated embodiment, the operating mode of the inverter circuit 12 can be set via an operating mode setting device 14, which is coupled to the input side of the electric machine 11. In particular, the operating mode setting device 14 can be used to set whether the inverter 13 operates in two-level operation, three-level operation, multi-level operation, or mixed operation. Mixed operation is an operating mode in which the inverter operates in both two-level operation and three-level or multi-level operation, which occurs, for example, when transitioning from one operating mode to the next. The structure and operating modes of the operating mode setting device 14 are described in more detail below with reference to Figures 4 to 6 below.

[0125] The electric machine 11 is a synchronous machine 11, preferably, but not necessarily, a three-phase synchronous machine 11. In this case, the inverter circuit 12 preferably includes a three-phase inverter 13.

[0126] It is also preferred if the electric machine 11 of the electric drive system 10 is a wheel hub motor for an electric vehicle, however, other applications are also conceivable and may be advantageous.

[0127] FIG. 3 is a schematic cross-sectional view showing an example of the synchronous machine 11 of the electric drive system according to the present invention shown in FIG.

[0128] An essential aspect of the present invention is the fact that the synchronous machine or electric machine 11 comprises a double rotor 20, which is further constituted by a flux-carrying material made of a solid material. A cross section of the double-rotor synchronous machine 11 is shown in FIG. 3. The double-rotor machine 20 comprises an outer rotor 21 and an inner rotor 22. A stator 23 is arranged between the two rotors 21, 22 in a manner known per se. The stator 23 may preferably, but not necessarily, be a yokeless stator 23.

[0129] The outer rotor 21 and the inner rotor 22 are preferably not laminated and are made of solid material. The inner rotor 22 is cylindrical. However, it is also conceivable to design the inner rotor 22 as a solid, full volume rotor.

[0130] In the illustrated example, two magnets 24, 25 with opposite poles are arranged on the inner surface of the outer rotor 21 in the outer air gap 26 between the outer rotor 21 and the stator 23. It is also conceivable and advantageous for the magnets 24, 25 to be embedded in pocket-like recesses in the outer rotor 21 specially provided for this purpose. However, it is also conceivable for the magnets 24, 25 to be spaced apart from the outer rotor 21, i.e., not arranged directly on its inner surface. The magnetic field lines 27 between the north and south poles of the magnets 24, 25 with opposite poles run in this case within the core material of the outer rotor 21.

[0131] Two magnets 28, 29 with opposite poles are arranged between the inner rotor 22 and the stator 23, in the illustrated example also on the outer surface of the inner rotor 22 within the inner air gap 30. Again, the magnets 28, 29 may be embedded in corresponding pockets in the inner rotor 22 or may be spaced apart from the inner rotor 22. In this case, the magnetic field lines 31 between the north and south poles of the magnets 28, 29 with opposite poles pass through the core material of the inner rotor 22.

[0132] The magnetic flux carrying material of the outer rotor 21 and / or the inner rotor 22 preferably consists of solid iron or a corresponding solid iron alloy.

[0133] FIG. 4 is a block diagram of a three-level or multilevel inverter circuit for an electric drive system corresponding to FIG.

[0134] As already explained with reference to FIG. 2, the inverter circuit 12 comprises two power supply terminals 16, 17, a load output 15, a three-level or multilevel inverter 13, and an operation mode setting device .

[0135] A first supply potential V11, for example a positive supply potential, can be connected to the first power supply terminal 16. A second supply potential V12, for example a negative supply potential or a reference potential, can be connected to the second power supply terminal 17. A supply DC voltage VDC = V11 - V12 is then present between the power supply terminals 16, 17.

[0136] A multiphase load current I1 is connected to the load output 15, and each phase of the electric machine 11 connectable via the load output 15 is operated.

[0137] A controllable three-level or multilevel inverter 13 is arranged between power supply terminals 16, 17 and a load output 15. The inverter 13 is designed to convert a DC voltage VDC taken on the supply side into an AC voltage VAC in order to supply a multiphase load current I1 to the load output.

[0138] The inverter 13 has a first driver stage 40 and at least one second driver stage 41. The second driver stage 41 is designed to provide a smaller output load current to the load output 15 than the output load current provided by the first driver stage 40.

[0139] The operating mode setting device 14 serves the purpose of setting and controlling the operating mode of the inverter 13, and therefore the operating mode of the entire inverter circuit 12. In particular, the inverter 13 is designed to operate in either a first operating mode of three-level or multi-level operation, or a second operating mode of two-level operation. It is also conceivable to have a third operating mode including a mixture of two-level and three-level or multi-level operation. The third operating mode is particularly envisioned and useful when transitioning from the first operating mode to the second operating mode and vice versa.

[0140] The operating mode setting device 14 thereby controls the operating mode of the inverter 13 used depending on the overall efficiency of the entire electric drive system 10. The overall efficiency is thereby a function of the detected phase current of the electric machine 11 and at least one other parameter affecting the overall efficiency and / or other characteristics of the electric machine 11 that affect the overall efficiency.

[0141] To set the respective operating mode to be used, the operating mode setting device 14 comprises at least one of the following devices: - evaluation device 42, - first measuring device 43, - second measuring device 44, - control unit 45.

[0142] The evaluation device 42 is designed to optimize the overall efficiency of the electric drive system 10 based on not only the phase currents but also at least one other parameter and / or at least one other characteristic. This can be done, for example, in situ, i.e., while the electric drive system 10 is operating. However, preferably, the relatively computationally intensive calculations are performed in advance, for example, by suitable calculations (e.g., numerical or analytical) and / or using a predetermined family of characteristics. For example, the numerical efficiency calculations for 2L and 3L operation and the mapping of functions with the determined outputs are performed in advance, i.e., offline. Similar to (but not limited to) the application of lookup tables to the efficiency calculations, the selection of a better efficiency using switching can also be performed more or less dynamically during operation.

[0143] For optimization, the evaluation device 42 includes an optimization module 46. The optimization module 46 first calculates the overall efficiency, which is then optimized analytically or via a look-up table, e.g., via an optimization function, taking into account the phase currents and at least one other parameter and / or characteristic.

[0144] The operating mode setting device 14 further comprises a first measuring device 43 and / or a second measuring device 44. For example, the first measuring device 43 comprises at least one sensor input 47. Thus, the operating mode setting device 14 can be coupled to the electric machine 11 via the sensor input 47 to record and detect electrical or physical parameters of the electric machine 11, such as the phase current, temperature and / or rotor speed of the electric machine 11. The second measuring device 44 is arranged to detect, for example, the temperature and / or the intermediate circuit voltage of the inverter 13. Furthermore, the second measuring device 44 can also be used to detect the supply voltage VDC.

[0145] The actual control of the inverter is performed by a controller 45 specially provided for this purpose. The controller 45 sets the respective operating mode of the inverter 13, i.e., whether the inverter 13 operates in three-level, multi-level or two-level operation. For example, the controller 45 can control the inverter 13 to activate both driver stages 40, 41 in three-level or multi-level operation, and to deactivate the second driver stage 40 in two-level operation.

[0146] FIG. 5 is a circuit diagram of a particularly preferred embodiment of an inverter circuit according to the present invention.

[0147] A supply DC voltage VDC is supplied to power supply terminals 16 and 17, whereby a supply potential V11=VDC / 2 can be connected to the first power supply terminal 16 and a supply potential V12=−VDC / 2 can be connected to the second power supply terminal 17. A configuration is also possible in which a reference potential, for example the potential of the reference ground GND, is supplied to the second power supply terminal 17. In this case, the supply potential V11=VDC can be connected to the first power supply terminal 16.

[0148] An intermediate circuit 50 consisting of two series-connected intermediate circuit capacitors 51, 52 is connected to the input side of the inverter 13. The intermediate circuit 50 functions as an energy storage section.

[0149] The inverter 13 shown in FIG. 5 includes a t-type neutral point clamped inverter architecture.

[0150] For this purpose, the first outer driver stage in the illustrated three-phase inverter includes three half-bridge circuits 53a to 53c, each of which is also connected to the load side of the load path between power supply terminals 16 and 17. Center taps 54a to 54c of each of the half-bridge circuits 53a to 53c form output load terminals 15a to 15c of the inverter 13, respectively. Each of the half-bridge circuits 53a to 53c includes a first controllable power switch T1, T2, T3, designed as a high-side switch. These first power switches T1, T2, T3 are connected to a first power supply terminal 16. The first power switches T1, T2, T3 are designed to supply a first voltage level to the load output 15. Furthermore, each of the half-bridge circuits 53a to 53c includes a second controllable power switch T4, T5, T6, which is a low-side switch, connected to a second power supply terminal 17. The second power switches T4, T5, T6 are designed to supply a second voltage level to the load output 15.

[0151] The second inner driver stage 41 is connected between the center tap 55 of the intermediate circuit and the output load terminals 15a to 15c, and thus between the center taps 54a to 54c of each of the half-bridge circuits 53a to 53c. In the illustrated example, the second driver stage 41 comprises three circuit branches 56a to 56c, respectively. Each of the circuit branches 56a to 56c comprises a series circuit of two controllable power switches T7 / T8, T9 / T10, and T11 / T12 arranged antiparallel to the load path. The controllable power switches T7 / T8, T9 / T10, and T11 / T12 are designed to provide a third voltage level at the load outputs 15a to 15c that is between the first and second voltage levels.

[0152] To drive each controllable power switch, the control device 45 comprises a first control unit 45a and a second control unit 45b. The first control unit 45a is designed to control the power switches T1 to T6 of the first driver stage 40. The second control unit 45b is designed to control the power switches T7 to T12 of the second driver stage 41.

[0153] In the example embodiment of Figure 5, inverter 13 is of a hybrid type. In this case, the power switches of inverter 13 are not made of the same semiconductor technology and / or the same switch type. In particular, in the example shown, power switches T1 to T6 are formed of Si-IGBTs with Si freewheeling diodes. Power switches T7 to T12 are formed as SiC-MOSFETs.

[0154] Alternatively (not shown in FIG. 5), the power switches T7 to T12 can be designed as SiC MOSFETs, and the power switches T1 to T6 can be designed as GaN MOSFETs.

[0155] Alternatively (also not shown in FIG. 5), the power switches T7 to T12 can be designed as IGBTs with freewheeling diodes, and the power switches T1 to T6 can be designed as GaN power switches, in particular GaN-MOSFETs.

[0156] Alternatively (also not shown in FIG. 5), in a so-called homogeneous inverter topology, all power switches T1 to T12 of inverter 13 may be of the same switch type and / or manufactured with the same semiconductor technology, e.g., designed as GaN power switches, SiC power switches such as SiC-MOSFETs.

[0157] Figure 6 shows a flow chart of a method for operating an electric drive system according to the invention, such as the drive system according to Figure 2, which comprises a synchronous machine with a double rotor, the double rotor being made of a solid magnetic flux-carrying material.

[0158] In a first step S1, the overall efficiency of the electric drive system is determined, for example, offline. For this purpose, the phase currents of the electric machine of the electric drive system are first detected (S11). Furthermore, at least one other parameter (S12) and / or at least one other characteristic that influences the overall efficiency of the electric machine is determined (S13).

[0159] Based on all this information, in the second step S2, a synchronous machine is operated. For this purpose, a controllable three-level or multilevel inverter circuit is used. The controllable three-level or multilevel inverter of the inverter circuit is operated in either a three-level or multilevel operating mode S21 or a two-level operating mode S22, depending on the overall efficiency of the electric drive system and the parameters and characteristics that affect it.

[0160] A hybrid of three-level or multi-level operation with two-level operation is also possible. Such a hybrid operation is possible and advantageous, for example, when going from three-level or multi-level operation to two-level operation to avoid abrupt switching, which may involve losses and result in reduced efficiency.

[0161] FIG. 7 is a schematic vertical cross-sectional view of the stator 101.

[0162] This is a schematic diagram of a synchronous machine 110 designed as a radial flux double rotor machine according to another embodiment (see FIG. 8), in particular a stator 101 for a wheel hub motor. The stator comprises a stator core 102, windings 103 and a support device 105. The stator core 102, windings 103 and support device 105 are designed to be rotationally symmetrical about the central axis M shown.

[0163] The windings 103 are self-supporting for torque support of the stator, and protrude beyond the stator core 102 at at least one axial end 104. The support device 105 is arranged axially offset from the stator core 102 and is connected by fitting to the windings 103 at at least one axial end 104 for torque support. In this way, torque applied to the stator core 102 during operation of the radial flux double-rotor machine 110 can be supported by the self-supporting windings 103 on the support device 105.

[0164] The windings 103 are made of a conductive material with low electrical resistance, preferably copper. The stator core 102 is preferably made of a soft magnetic material for magnetic flux propagation. The support device is preferably made of a thermally conductive material, for example, an aluminum alloy. Of course, the windings 103 are electrically insulated.

[0165] FIG. 8 is a schematic longitudinal sectional view of a radial flux double rotor machine.

[0166] This is also a purely illustrative schematic diagram. Thus, a synchronous machine 110 designed as a radial flux double rotor machine comprises, in addition to the stator 101 in Fig. 7, a mechanically fixed base 111, a first rotor 112, and a second rotor 113. The stator core 102, windings 103, support device 105, base 111, first rotor 112, and second rotor 113 are also designed to be rotationally symmetrical about the central axis M shown.

[0167] The windings 103 are self-supporting for torque support of the stator 101, protrude beyond the stator core 102 at at least one axial end 104, and are supported by a base 111 via a support device 105. The support device 105 is disposed offset in the axial direction from the stator core 102, and is connected by fitting to the windings 103 at at least one axial end 104 for torque support. In this case as well, the support device 105 is fixed to the base 111 so that torque is supported by the base 111 via the support device 105.

[0168] The first rotor 112 is disposed radially inward of the stator core 102, and the second rotor 113 is disposed radially outward of the stator core 102. The base 111 may be formed, for example, as a machine housing, and here, purely by way of example, consists of an L-shaped structure represented by two legs 107, 108. The illustration is not intended to be exhaustive, and rather the base may include other components and / or structural parts. The first leg 107 extends substantially radially, and the second leg 108 extends substantially axially at a position furthest from the central axis M.

[0169] Purely diagrammatically, the support device 105 is shown as one radially extending piece, but it may also be provided in multiple pieces and / or with different shapes designed to matingly engage with the windings 103. The overlap of the windings 103 with the base 111 is depicted purely for illustrative purposes and does not imply a direct connection. The windings 103 are preferably connected to the base 111 via the support member 105 for torque support.

[0170] The radial flux double rotor machine 110 shown in FIG. 8 can be used as the synchronous machine 11 of the electric drive system 10 shown in either FIG. 1 or FIG. 2, and in combination with the inverter circuit 12 shown in any of FIGS. 4 to 6.

[0171] FIG. 9 is an exploded perspective view of a stator 101 according to another embodiment.

[0172] The stator 101 comprises windings 103, a stator core 102 and a support device 105, advantageous exemplary embodiments of which components are shown here in more detail and in perspective view.

[0173] The winding 103 is composed of an inner layer and an outer layer in which a plurality of conductor bars 106 are connected to each other in a rod-like shape. The conductor bars 106 of the inner layer and the outer layer are arranged spirally in opposite directions, and at both ends of the conductor bars, they are material-bonded to radial conductor bar pieces 117 that connect the inner layer and the outer layer.

[0174] The thickness of the inner and outer layers corresponds to the thickness of the conductor bars 106. That is, the winding 103 is formed by a single conductor layer that forms a conductor loop and has a relatively large cross section in the form of each conductor bar 106.

[0175] The bar structure formed by the conductor bars provides the winding with torsional rigidity and thereby allows it to be self-supporting for torque support.

[0176] The conductor bars 106 thus form undulating winding strands which may be interconnected to form a rotating field generating winding of any number of strands by corresponding interconnection means such as delta connection, star connection, etc. which are known to those skilled in the art and therefore will not be described further.

[0177] In the illustrated embodiment, the stator core 102 and the support device 105 are each made up of, for example, two parts. To assemble the stator 101, the windings 103, the stator core 102, and the support device 105 are nested within one another. After assembly, the components are aligned concentrically along a common central axis M. The support device 105, which is made up of two parts as illustrated here, is positioned axially offset relative to the other components and forms the innermost and outermost components of the stator 101. These are the inner and outer rings, each formed with grooves for mating engagement with the conductor bars.

[0178] The illustrated two-piece stator core 102 is formed by two laminated stator cores 118 that are helically twisted relative to one another and will be described in more detail with reference to FIG.

[0179] In other embodiments, the stator core 102 and the support device 105 may each be formed of one part or two or more parts.

[0180] FIG. 10 is an exploded perspective view of a radial flux double rotor machine 110 according to one embodiment.

[0181] In addition to the components of the stator 101, the radial flux double-rotor machine 110 also includes a first rotor 112, a second rotor 113, and a base 111. The first rotor 112 is arranged radially inside the stator core 102, and the second rotor 113 is arranged radially outside the stator core 102. The rotors 112 and 113 are preferably made of a soft magnetic solid material and have permanent magnets, so-called surface magnets, as magnetic poles on their surfaces facing the stator core. In other embodiments, other rotors known to those skilled in the art can also be used, such as embedded magnets, squirrel-cage rotors, or electrically excited rotors.

[0182] The base 111 is shown here only diagrammatically for the sake of clarity. As already mentioned in the description of Figure 8, the base 111 is fixed in the assembled state to the support device 105. The base 111 is mechanically fixed to the base system, for example the support of the axle.

[0183] The radial flux double rotor machine 110 shown in FIG. 10 can be used as the synchronous machine 11 in the electric drive system 10 shown in either FIG. 1 or FIG. 2, and in combination with the inverter circuit 12 shown in any of FIGS. 4 to 6.

[0184] FIG. 11 is an exploded perspective view of a radial flux double-rotor machine 110 according to another embodiment. The radial flux double rotor machine 110 has substantially the same components as those described herein with reference to Figures 9 and 10. Shown assembled on the left side of the figure are the stator core 102, windings 103, first rotor 112 and second rotor 113.

[0185] The support device 105 shown on the right is also formed of two parts, each having a different configuration: an annular inner support member 127 and an outer support member 128. The support members 127, 128 are provided with support grooves 126. The support grooves 126 are provided in the inner peripheral surface of the outer support member 128 and the outer peripheral surface of the inner support member 127 to engage with the conductor bars 106 of the winding 103.

[0186] For this purpose, the support grooves 126 are angled axially according to the helical path of the conductor bars 106 of the windings 103 or their pitch so as to be able to engage with them.

[0187] The support members 127, 128 are preferably made of a conductive metal, most preferably an aluminum alloy. The two-piece design of the support members 127, 128 allows the support groove 126 to be easily accessible for mechanical or machining operations during manufacture.

[0188] The inner support member 127 and the outer support member 128 each have a plurality of holes 109 in the circumferential direction for fastening to the base 111. By way of example, the holes 109 are here evenly distributed around the circumference. The individual holes 109 are located slightly outside the body of the support member, and the support members 127, 128 thus each form a circumferential star shape pointing away from the windings. Of course, other distributions of the holes 109 are possible, and other types of fastening means for connection to the base 111 are also conceivable.

[0189] FIG. 12 is a perspective view of the radial flux double rotor machine 110 of FIG. 11 in an assembled state.

[0190] The support device 105 is fixed to a machine housing (not shown), for example, as a base 111, through holes 109, thereby transmitting torque to a mechanically fixed portion of the radial flux double rotor machine 110. In this way, the torque generated by the radial flux double rotor machine 110 can be effectively supported. The support device 105 is fixed using appropriate fasteners (not shown), such as screws.

[0191] The conductor bars 106 of the winding 103 extend to the outside of the stator core 102 and the first and second rotors 112, 113 on both axial sides. The conductor bars 106 arranged spirally on the inner and outer radial sides are connected to each other on the outside of the stator core 102.

[0192] Support members 127, 128 are shown here engaged with conductor bars 106 of winding 103. It can be seen that conductor bars 106 are disposed in each support groove 126, and all conductor bars are coupled to the support device by fitting. Thus, torque supported by winding 103 can be supported to base 111 attached to hole 109 via support device 105.

[0193] The radial flux double rotor machine 110 shown in Figures 11 and 12 may also be advantageously used as the synchronous machine 11 in the electric drive system 10 shown in either Figure 1 or Figure 2, and in combination with the inverter circuit 12 shown in any of Figures 4 to 6.

[0194] FIG. 13 is a vertical cross-sectional perspective view of a radial magnetic flux double-rotor machine 110 according to another embodiment.

[0195] This embodiment is substantially similar to the assembled radial flux double rotor machine 110 shown in Figure 10, the components of which are described in more detail below.

[0196] The stator core 102 has an inner subpackage 123 and an outer subpackage 124. The subpackages 123, 124 extend annularly between the first rotor 112 and the second rotor 113. Based on the cross-sectional view, it is also possible to see the inner layer 114 and outer layer 115 of the conductor bars 106 extending inside the subpackages 123, 124.

[0197] The illustrated radial flux double-rotor machine 110 has a so-called "yokeless" design, in which a yoke is not functionally located between two teeth in the associated magnetic flux. Thus, the stator yoke 130 extends between the conductor bars 106, but serves only to mechanically hold the laminated stator core 118. The radial yoke thickness can be correspondingly thin, and in the illustrated embodiment, is illustratively approximately 10% of the total radial stator thickness. Furthermore, the relatively thin yoke thickness reduces undesirable leakage flux within the yoke. In other embodiments, the radial yoke thickness can be less than 30%, preferably less than 20%, and particularly preferably less than 10% of the total radial stator thickness for this purpose.

[0198] The support device 105 comprises an inner support member 127 and an outer support member 128. In this case, the support members 127, 128 are clearly arranged axially offset relative to the stator 101 and rotors 112, 113. Furthermore, the form-fitting engagement of the support members 127, 128 with the conductor bars 106 of the inner layer 114 and outer layer 115 is visible at least in cross section.

[0199] Furthermore, it can be clearly seen here that the conductor bars 106 of the inner layer 114 and the outer layer 115 are connected at their ends 116 by radially arranged conductor bar pieces 117. This connection is preferably produced as a material joint, for example by laser welding.

[0200] Additionally, this cross section shows the surface magnets of rotors 112 and 113. First rotor 112 has multiple permanent magnets attached to its outer circumferential surface, while second rotor 113 has multiple permanent magnets attached to its inner circumferential surface.

[0201] A particularly advantageous embodiment occurs when the rotor is made of a soft magnetic solid material and the permanent magnets are surface mounted, as this design allows the rotor to be manufactured very cheaply and achieves high efficiency.

[0202] FIG. 14 is an exploded perspective view showing laminated stator core 118 of stator core 102. As shown in FIG.

[0203] As mentioned above, the laminated stator core 118 of the stator core 102 has an inner subpackage 123 and an outer subpackage 124. This helps simplify the manufacture of the counter-twisted stator slot 119 by stacking identical inner and outer stator laminations 121, 122, with recesses in the same locations, in a twisted relationship with respect to one another.

[0204] In other embodiments, the stator laminations may be manufactured in one piece to provide multiple differently shaped stator laminations with differently positioned recesses and stacked in the required order to form the stator slots. In still other embodiments, a fully unitary stator core 102 is also contemplated, which may be manufactured additively, for example.

[0205] In the two-piece design shown, the inner diameter of the outer subpackage 124 is approximately equal to the outer diameter of the inner subpackage 123. This allows the inner subpackage 123 to be coaxially positioned within the outer subpackage 124.

[0206] The subpackages 123 and 124 are constructed by stacking individual annular stator laminations 121 and 122 one on top of the other. The stator laminations 121 of the outer subpackage 124 are manufactured with recesses distributed around their outer periphery to form the outer stator slots 119. The stator laminations 122 of the inner subpackage 123 are manufactured with recesses distributed around their inner periphery to form the inner stator slots 120. For example, manufacturing these stator laminations by pressing is advantageous for edge quality and very low manufacturing costs.

[0207] The inner stator slot 119 and the outer stator slot 120 represent spirals that extend in opposite directions with the same pitch and are characterized by a stator slot sweep angle α, which can be defined as the angle between the positions of the same stator slot on one axial side of the stator core 102 and on the other axial side of the stator core 102 about the central axis M.

[0208] The stator slots 119, 120 are here exemplarily designed as T-slots with tapered rectangular recesses. They are provided in particular for matingly receiving conductor bars with rectangular cross sections. Of course, the shape of the recesses or stator slots can be adapted to the shape of the conductors. Other cross-sectional shapes are also conceivable for this purpose.

[0209] FIG. 15 is a schematic vertical cross-sectional view of the stator slots 119 and 120.

[0210] The usable or continuous gap width a of the stator slots 119 , 120 in the laminated stator core 118 is formed to be substantially equal to the width of the conductor bars 106 housed within the stator core 102 .

[0211] The stator lamellas 121, 122 have straight, in particular stamped, edges. Due to the offset of the lamellas relative to one another, the width b of the recesses provided for the stator slots 119, 120 is made larger than the width d of the conductor bar 106 by an amount predetermined by the pitch δ of the spiral shape of the paths and the thickness t of the lamellas.

[0212] In FIG. 15, the conductor bar 106 is shown schematically in dashed lines within the stator slots 119, 120, with the continuous gap width a of the stator slots 119, 120 being slightly larger than the width d of the conductor bar 106 to provide a clearance fit, and the width b of the recesses in the stator plates 121, 122 being significantly larger than the gap width a.

[0213] In the case of straight edges, e.g., of stamped sheet metal, the sheet thickness t and the pitch angle δ of the slot path are important factors influencing the difference between the width b of the recess and the available passage gap a in the slot. This difference arises to compensate for the pitch angle on the one hand and the step-like difference of the laminated core on the other hand.

[0214] In the limit of an infinitesimally thin plate, that is, when the pitch angle δ of the conductor bars is taken into pure consideration, the minimum size of the width b of the recess is as follows: b=1 / cos(δ)*d

[0215] The width b of the recess is actually provided to be even larger in order to compensate for the actual plate thickness on the one hand and to provide a clearance fit that allows the insertion of the conductor bar on the other hand.

[0216] 15 is dimensioned so that the gap width a of the stator slots 119, 120, reduced by the offset between the recesses in the stator laminations, forms a predetermined clearance fit with the width d of the conductor bar 106 inserted in the stator slot, but the contact is still close enough to provide a uniformly distributed power transmission or torque support between the stator laminations and the windings. Such dimensioning is achieved, inter alia, by the fact that, on the one hand, each stator lamination is uniformly formed with high edge quality and twisted with a uniform offset, and, on the other hand, only a single conductor bar 106 is placed in each stator slot 119, 120, the dimensions of which are constant.

[0217] In particular, in the illustrated embodiment, the conductor bar 106 is a bar of rectangular cross section having a side length or width of a few mm, for example in the range of 2 mm to 6 mm, in particular in the range of 3 mm to 5 mm, and preferably a rectangular cross section of 5 mm x 3 mm.

[0218] FIG. 16 is a perspective view of the winding 103.

[0219] The winding 103 is constituted by conductor bars 106 which extend helically along a central axis M. For this purpose, the conductor bars 106 are not only arranged in a corresponding interlaced manner, but are also twisted relative to one another according to a helical path.

[0220] The sweep angle β of the conductor bar 106 determines the angle between the start and end of the conductor bar 106 relative to the central axis M. The helical pitch of the conductor bar 106 is equal to the helical pitch of the stator slots 119, 120, but because the conductor bar 106 is longer than the stator slots, the ratio of the respective sweep angles α, β can be formed to characterize a geometric relationship, also known as the pole coverage. To provide an optimum between magnetic losses and torque utilization in a radial flux double-rotor machine, this ratio (pole coverage) preferably ranges between 0.6 and 0.75.

[0221] The opposite twist of the radially inner and outer layers 114, 115 of the conductor bar 106 can be seen here as well. This twist is such that the cross section of the conductor bar relative to a radial line passing through its center is always the same at any point on the conductor bar, also known as a 2.5D shape. Thus, the conductor bar ends of the inner and outer layers 114, 115 are positioned one on top of the other in the same orientation. Thus, the conductor bars 106 of the radially inner and outer layers 114, 115 can be electrically connected in a simple manner, here by means of radially extending conductor bar pieces 117, which are exemplarily welded to the conductor bar 106.

[0222] It should be noted that the windings illustrated here are not manufactured separately, but are always manufactured in combination with the stator core 102, as will be explained in more detail with reference to FIG.

[0223] FIG. 17 is a side view of the winding 103.

[0224] The precise radial alignment of the conductor bars at each point of the helical path, which in the illustrated side view are aligned in the region of the central axis M, can be clearly seen in this view. Each of the ends 116 of the conductor bars forms a connection point between the radially inner layer 114 and the radially outer layer 115.

[0225] In the illustrated embodiment, the winding has, by way of example, a total of twelve terminal contacts 131. With a three strand interconnection, three-phase operation is preferably provided. However, the winding can be adapted to other interconnections to form a rotating field generating winding with any number of strands, in a manner known in the art.

[0226] FIG. 18 is a perspective view showing an FEM simulation of the loaded winding 103.

[0227] Although some simplifications were made for the simulation, this is essentially the winding shape shown in Figure 16. The scale shown indicates the stress within the winding, and therefore, for example, when the cross-sectional shape of the conductor bar 106 is a rectangle of 5 mm x 3 mm, the scale is 0 MPa to 30 MPa.

[0228] In this example, the ends of the conductor bars are defined by a sweep angle β>0 of the conductor bars, i.e., they are arranged and formed in a spiral or shaped in a corresponding twisted manner. At the axial ends where the support device engages, the maximum torque of the radial flux double-rotor machine 110 of corresponding dimensions is illustrated by a thick arrow, and for example, if the cross-sectional shape of the conductor bars 106 is a rectangle of 5 mm x 3 mm, the maximum torque may be 1000 Nm or more, in particular 1500 Nm or more, in a specific example about 2000 Nm, and in another specific example about 5000 Nm.

[0229] It is clear that the spiral shape ensures a very uniform distribution of stress within the winding. Despite being greatly exaggerated, there is almost no deformation. Therefore, this design significantly reduces stress peaks and, therefore, deformation.

[0230] The bar-like structure allows high torques to be absorbed autonomously by the windings 103 without causing unacceptably large deformations and / or stress states when fixing the axially accessible winding ends. This is due in particular to the fact that the conductor bars 106 of the bar structure mainly absorb tensile and compressive stresses when subjected to tangential forces.

[0231] This significantly reduces mechanical stress compared to designs using axially parallel straight conductors.

[0232] FIG. 19 is a perspective view of a model comparing a linear design and an axial path of the conductor bar 106 under load.

[0233] Comparing with Fig. 18, it can be seen that the linear design and axial path of the conductor bar cause the stress path to be concentrated as shown on the left side of Fig. 18, and large deformation of the conductor bar occurs due to locally high stress accompanied by large deformation as shown on the right side of Fig. 19. Here, the same stress scale and the same exaggerated deformation as Fig. 18 are set to show the effect of differences in structural arrangement on torsional rigidity.

[0234] FIG. 20 is a flowchart of a method for manufacturing the stator 1.

[0235] The method includes a first step S1 of providing a stator core 102 having radially outer stator slots 119, each spiraling, and radially inner stator slots 120, each spiraling in an opposite direction. A next step S2 involves inserting individual conductor bars 106 along a spiral through the inner stator slots 119 and the outer stator slots 120. The conductor bars are inserted, in particular, axially. A further step S3 involves connecting the conductor bars 106 inserted in the inner and outer stator slots at their ends 116 to form conductor loops.

[0236] Although the present invention has been fully described above with reference to the preferred embodiment, the present invention is not limited thereto and various modifications are possible. [Explanation of symbols]

[0237] 2 stator core 3 windings 10 Electric Drive System 11 Electrical machines, synchronous machines 12 (3-level or multi-level) inverter circuits 13 (3-level or multi-level) inverters 14 Operation mode setting device 15 Load Output 15a to 15c output load terminals 16,17 Power terminal 18 Supply voltage source 20 Double rotor, double rotor machine 21 outer rotor 22 inner rotor 23 Stator 24,25 (Outer rotor) magnets with opposite poles 26 (external) air gap 27 (outer) magnetic field lines 28,29 (inner rotor) magnets with opposite poles 30 (inner) air gap 31 (inner) magnetic field lines 40 First (outer) driver stage 41 Second (inner) driver stage 42 Evaluation equipment 43 1st measuring device 44 Second measuring device 45 Control Device 46 Optimization Module 47 Sensor Input 50 intermediate circuit 51,52 Intermediate circuit capacitor 53a~53c Half-bridge circuit 54a~54c Center tap 55 Center Tap I1 (polyphase) load current S1, S2 processing steps Substeps S11 to S13 S21, S22 substeps T1 to T3 First power switch of the half-bridge circuit, high-side switch T4-T6 Second power switch of the half-bridge circuit, low-side switch T7 to T12 power switches VAC (output side) AC voltage VDC (input side) DC voltage V11 (positive) supply potential V12 (negative) supply potential, reference potential 101 Stator 102 stator core 103 Winding 104 Axial end 105 Support device 106 Conductor Bar 107 1st leg 108 Second leg 109 holes 110 Radial flux double rotor machine 111 Base 112 First Rotor 113 Second Rotor 114 Radial outer layer 115 Radial inner layer 116 Conductor bar both ends 117 Conductor bar piece 118 Laminated stator core 119,120 stat lots 121,122 Stator thin plate 123 Inner Subpackage 124 outer subpackage 125 Support member 126 Support groove 127 Inner support member 128 Outer support member 129 Permanent Magnets α Sweep angle (stator slot) β Sweep angle (conductor bar) δ pitch a Gap width b Recess width d Conductor bar width M center axis t plate thickness

Claims

1. At least one synchronous machine (11; 110) comprising double rotors (21, 22; 112, 113) and distributed windings (3; 103) arranged in a stator core (2; 102), wherein the double rotors (21, 22; 112, 113) are made of a magnetic flux propagation material made of a solid material, and the synchronous machine (11; 110) comprises a first rotor (22; 112) made of a solid material arranged radially inside the stator core (2; 102) and a second rotor (21; 113) made of a solid material arranged radially outside the stator core (102), wherein the windings (3; 103) are designed to be self-supporting for torque support; and at least one three-level or multilevel inverter circuit (12) coupled to the synchronous machine (11; 110) at a load output (15) and designed to convert a DC voltage received on the supply side into an AC voltage capable of driving the synchronous machine (11; 110) via the load output (15), the inverter circuit (12) having a controllable three-level or multilevel inverter (13).

2. 2. An electric drive system according to claim 1, wherein the synchronous machine (11; 110) is an electrically operable wheel hub motor for a motor vehicle.

3. 3. An electric drive system according to claim 1 or claim 2, wherein the synchronous machine (11; 110) is a radial flux double rotor machine (110).

4. 3. The electric drive system according to claim 1, wherein the windings (103) protrude beyond the stator core (102) at at least one axial end (104), and a support device (105) is provided, the support device being axially offset relative to the stator core (102) and designed to matingly engage with the windings (103) at the at least one axial end (104) for torque support.

5. 5. The electric drive system according to claim 4, wherein the synchronous machine (11; 110) has a mechanically fixed base (111), and the support device (105) is engaged with at least one axial end (104) of the winding (103) by mating for torque support and is supported by the base (111).

6. 3. An electric drive system according to claim 1 or claim 2, wherein the magnetic flux carrying material of the rotor (21, 22; 112, 113) is iron or an iron alloy.

7. 3. The electric drive system of claim 1, wherein the inverter circuit (12) comprises an operating mode setting device (14) designed to change the inverter (13) from three-level or multi-level operation to two-level operation, or vice versa, depending on the overall efficiency of the electric drive system (10), the overall efficiency being a function of the detected phase currents of the synchronous machine, at least one other parameter affecting the overall efficiency, and / or other characteristics of the synchronous machine (11; 110) that affect the overall efficiency.

8. 2. The electric drive system of claim 1, wherein the inverter circuit (12) comprises an operating mode setting device (14) designed to change the inverter (13) from three-level or multi-level operation to two-level operation, or vice versa, depending on the overall efficiency of the electric drive system (10), the overall efficiency being a sole function of detected phase currents of the synchronous machine or a function of at least one other characteristic of the synchronous machine (11; 110) that affects the overall efficiency.

9. 2. The electric drive system of claim 1, wherein the inverter (13) comprises a first driver stage (40) and at least one second driver stage (41), the second driver stage (41) being designed to supply an output load current to the load output (15) that is less than the output load current supplied by the first driver stage (40).

10. 10. The electric drive system of claim 8 or claim 9, wherein the operating mode setting device (14) comprises a control device (45) designed to control the inverter (13) to activate the first driver stage (40) and the second driver stage (41) in three-level or multi-level operation and to deactivate at least one of the driver stages (40), (41) in two-level operation.

11. 11. The electric drive system of claim 10, wherein the first driver stage (40) comprises at least one bridge circuit, in particular a half-bridge circuit (53a)-(53c), the center tap of which forms the output load terminal (15a)-(15c) of the inverter circuit (12), each bridge circuit comprising at least one first power switch (T1)-(T3) connected to a first power supply terminal (16) and designed to supply the load output (15) with a first voltage level, and each bridge circuit further comprising at least one second power switch (T4)-(T6) connected to a second power supply terminal (17) and designed to supply the load output (15) with a second voltage level.

12. 10. The electric drive system of claim 9, wherein the second driver stage (41) comprises at least one third power switch, the load path of which is connected in series between an intermediate circuit (50) and the center tap of the first driver stage, and which is designed to supply a third voltage level to the load output (15), the third voltage level being between the first and second voltage levels.

13. 9. The electric drive system of claim 8, wherein the operating mode setting device (14) comprises an evaluation device (42) designed to optimize the overall efficiency based on the phase currents or the at least one other characteristic.

14. The electric drive system of claim 1 or claim 2, wherein the inverter (13) comprises a t-type neutral point clamped inverter architecture.

15. 4. The electric drive system according to claim 3, wherein the windings (103) are designed to have a torsional rigidity such that a torque acting on the stator core (102) during operation of the radial flux double-rotor machine (110) can be supported, in particular completely, by the support device (105) via the windings (103).

16. The electric drive system of claim 15, wherein the stator core (102) is designed to carry primarily radial magnetic flux.

17. 17. The electric drive system of claim 16, wherein the stator core (102) has a radial yoke thickness of less than 30%, preferably less than 20%, more preferably less than 10% of the overall radial thickness of the stator core.

18. 3. An electric drive system according to claim 1 or 2, wherein the winding (103) is formed from conductor bars (106) connected to one another, in particular in a rod-like manner.

19. 20. The electric drive system of claim 18, wherein the winding (103) comprises a radially inner layer (115) of helically arranged conductor bars (106) and a radially outer layer (114) of helically arranged conductor bars (106) in an opposite direction.

20. 20. The electric drive system of claim 19, wherein the radially inner layer (115) and the radially outer layer (114) of the winding (103) each have a thickness of a single conductor bar (106).

21. 20. The electric drive system of claim 19, wherein the conductor bars are each twisted according to a helical path such that the cross section of the conductor bar is the same at each point on the conductor bar relative to a radial axis of the cross section.

22. 20. The electric drive system of claim 19, wherein the conductor bars (106) of the radially inner layer (115) and the radially outer layer (114) belonging to the same phase of the winding (103) are connected to each other at their ends (116), in particular by radially arranged conductor bar pieces (117) and / or by material joints.

23. 20. The electric drive system of claim 19, wherein the stator core (102) comprises a laminated stator core (118) having stator slots (119, 120) that extend helically according to a winding path, and a single conductor bar (106) is disposed within each stator slot (119, 120) of the laminated stator core (118).

24. 20. The electric drive system according to claim 4, claim 5 or claim 19, wherein the support device (105) has a support member (125) provided with a support groove (126) that corresponds to the spiral arrangement of the conductor bar (106) and engages with the conductor bar (106).

25. 25. An electric drive system according to claim 21 or claim 24, wherein the support groove (126) at least partially follows the helical path of the twisted conductor bar (106), in particular has an equally twisted path.

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