DE102018202005A1 - Electric machine and method for operating an electric machine - Google Patents

Abstract

The invention relates to an electric machine (2), in particular an electric drive machine for a motor vehicle, comprising: - an annular rotor (6) formed around a rotation axis (R) and rotatable about the rotation axis (R), - an annular stator ( 4) which is arranged around the rotation axis (R) such that it surrounds the rotor (6) concentrically concentrically, such that viewed in a radial direction (5) between the rotor (6) and the stator (4) an air gap ( 14), wherein the stator (4) has two three-phase, in operation controllable winding sets (12a, b) and a control unit (22) which is set up and configured such that in operation from the control unit (22) to a Actuation of the electric machine (2) the winding sets (12a, b) with a three-phase current (l ~) are acted upon and thereby a magnetic rotary field (B) in the air gap (14) adjusts to produce a on the rotor (6) acting D torques (M), wherein the course of the magnetic rotating field (B) by a superimposition of a sinusoidal fundamental wave (GW) with sinusoidal harmonics (OW) is approximated and the control unit (22) for controlling the electric machine (2) is formed in different operating modes , wherein in dependence on a predetermined machine requirement during operation, the electric machine (2) is controlled with one of these operating modes.

Description

The invention relates to an electrical machine and a method for operating an electrical machine.

Electric machines, in particular electric motors are used today in various applications. In this connection, various types and shapes of electric machines exist.

Electric machines are also used in electrically driven vehicles as an electric drive machine. Under electric drive machine in the present case are understood in particular electrical machines that produce a propulsion in the form of a torque for a motor vehicle. Typical performances of such electric drive machines have, for example, values of several 100 kW.

The various types and shapes of electrical machines usually have functional principle-related advantages and disadvantages.

For example, so-called asynchronous machines or reluctance machines are frequently used today in the motor vehicle industry.

In today's development of electrical machines, in particular of electric drive machines in motor vehicles, the focus is thus often in an optimization of the advantages and a reduction and preferably avoiding the disadvantages of a respective electric machine. Usually, a large part of the disadvantages of electrical machines across types and functions is due to electrical or magnetic losses. Under electrical losses are understood in the present general voltage or current-carrying losses, such as conductor losses. In the present case, magnetic losses are understood to mean losses which result in a weakening or scattering of a magnetic field necessary for the torque generation of the electrical machine and thus, for example, cause losses in efficiency.

Thus, the already mentioned asynchronous machine, for example, has the disadvantage that in the rotor of such a machine operating point-dependent and not negligible rotor losses occur.

A disadvantage of the reluctance machine also mentioned above is an increased reactive power demand, which has a negative effect on the efficiency, in particular when starting the machine.

Proceeding from this, the present invention seeks to provide an electric machine, especially an electric drive machine for a motor vehicle, which has an optimized efficiency. Furthermore, the invention has the object to provide a method for operating an electrical machine, which has an optimized efficiency.

The object is achieved by an electric machine with the features of claim 1 and by a method for operating an electrical machine having the features of claim 15.

Advantageous embodiments, developments and variants are the subject of the dependent claims. The advantages and preferred embodiments listed with regard to the electrical machine are to be transferred analogously to the method and vice versa. The method for operating the electrical machine is used in particular for operating the electrical machine described below. In the following description, the method for operating the electric machine will be discussed in parallel at the appropriate places and for better understanding of the description of the electrical machine. The electric machine is designed in particular as an electric drive machine for a motor vehicle.

The electric machine has an annular rotor which is designed to be rotatable about an axis of rotation and about the axis of rotation.

In addition, the electric machine has an annular stator, which is arranged around the axis of rotation such that it surrounds the rotor circumferentially and concentrically, such that, viewed in a radial direction, an air gap is formed between the rotor and the stator. The stator has two three-phase, in operation controllable winding sets, which are arranged offset by a predetermined angle to the stator. As a result, the winding sets form a discrete, symmetrical winding distribution. In the present case, three-phase winding sets which can be controlled during operation are specifically understood to mean that one set of windings each has three coils which, in the controlled state, are each connected to one phase of a three-phase network. In the present case, the electric machine is therefore a six-phase electrical machine.

In operation, a winding set, so three coils are energized with a three-phase current, so driven. That is, each coil of the respective winding set is with a preferably sinusoidal AC applied to a predetermined frequency.

In addition, the electric machine has a control unit which is set up in such a way that, during operation, the winding sets are subjected to the already explained three-phase current by the control unit. That the control unit is designed to set the predetermined frequency and / or an amplitude of the impressed three-phase current. Under stamped in the present case is understood in general the energization of the winding sets with the three-phase current. As a result, a rotating magnetic field rotating in the circumferential direction sets in the air gap, which serves to generate a torque acting on the rotor.

In the present case, the electrical machine is an electrical machine of the type of a so-called asynchronous machine. That is, in operation, the rotor does not rotate at the same speed as the rotating magnetic field. The rotor thus rotates asynchronously to the magnetic rotating field. The operating principle of asynchronous machines is basically known, so that a detailed description of this is dispensed with here.

The magnetic rotating field extends radially in the air gap, ie in or against the radial direction. In the circumferential direction, ie in the direction of rotation of the rotor, the magnetic rotating field has a course in the manner of a rectangular staircase signal, which is approximated by a superimposition of a sinusoidal fundamental wave with sinusoidal harmonics. In other words, the course of the magnetic rotating field can be approximated by means of the Fourier series development into a sinusoidal fundamental wave and a number of sinusoidal harmonics of odd order. Owing to the symmetrical winding distribution and the symmetrical magnetic field generated thereby, only odd orders of the harmonics occur in the aforementioned Fourier development of the magnetic rotating field. In this connection, the fundamental wave and the occurring harmonics of the rotating magnetic field course are often used for a description or explanation of machine-typical effects, e.g. the generation of the torque used by the magnetic rotating field. If, for example, a torque is mentioned here in a simplified manner, which is generated by a selected harmonic, it is to be understood that the selected harmonic does not generate the torque directly, but rather the rotating magnetic field which is approximated by the selected harmonic.

Such a consideration of the magnetic rotating field as a superimposition of a sinusoidal fundamental wave with sinusoidal harmonics can thus be used as representative of the magnetic field of rotation as a torque-generating factor within the electric machine. Harmonics continue to run depending on their order either in the direction of the magnetic rotating field or against the magnetic rotating field. For example, in the present machine every second harmonic occurring from the 5th harmonic (ie the 5th, 9th, 13th, etc.) runs in the direction of the magnetic rotating field. However, each intermediate harmonics (ie the 7th, 11th, etc.) run counter to the direction of the magnetic rotating field. In general, the harmonics that occur, for example, lead to undesirable parasitic torques that lead to increased noise, for example, during operation of the electric machine. The term "run the harmonics" is specifically understood in the present case that the extreme values of the respective sinusoidal waves remain constant in their distance from each other, but in the circumferential direction (when running in the direction of the magnetic rotating field) or counter to the circumferential direction (in a direction opposite to the direction of the Rotating field).

Thus, on the basis of an approximation of the magnetic rotating field, it is possible, with the aid of the control unit, to achieve optimized courses of the magnetic rotating field and thus of the generated torque by advantageous energizing of the winding sets. The prior art provides for this purpose to achieve a damping or suppression of the harmonics occurring.

In contrast to previous approaches that provide attenuation or suppression of the occurring harmonics, in this application, a solution is pursued in which one or more modes of operation is deliberately provided / are, in which / which at least one selected harmonic not suppressed, but still preferably amplified (compared to the fundamental).

The control unit is designed to control the machine in at least the following different operating modes.

In a first operating mode, the course of the rotating magnetic field that arises is mainly approximated by a selected harmonic. This mode of operation is also referred to as an efficiency-optimized mode of operation. In the first operating mode, the electric machine is operated in the manner of a reluctance machine, which will be discussed in more detail later in the description.

In a second mode of operation is the course of the adjusting magnetic Rotary field mainly approximated by the fundamental wave. The fundamental wave is the decisive wave for operation of the electric machine, which requires a high torque. Here, the machine is also operated in the manner of an asynchronous machine. For example, asynchronous machines have efficiencies> 90%, especially with high torque requirements. By high torque requirements are understood in the present example, torques corresponding to at least two-thirds of the maximum torque of the electric machine Thus, the second operating mode, for example, understood an operating mode in which a high torque for driving the motor vehicle, for example when driving uphill or when accelerating the motor vehicle from the state, is required. This operating mode is also called torque-optimized operating mode.

The two terms torque-optimized and effective wheel optimized serve in the present case primarily a more accurate and easier distinction. However, they do not limit the benefit of the particular operating mode. Rather, an essential aspect of the invention is to achieve advantages in terms of efficiency optimization both in the first operating mode and in the second operating mode.

In a third operating mode, the course of the rotating magnetic field that arises is approximated by a superposition of the fundamental wave with the selected harmonic.

By "mainly by the selected harmonic wave" is specifically understood here that when superimposing several harmonics with the fundamental wave for approximation of the course of the magnetic rotating field, the amplitude component of the selected harmonic> 90%. Specifically, the amplitude component of the selected harmonic is 100%. That The spin field is mathematically best approximated by the selected harmonic without parts of the fundamental wave. In other words, the torque acting on the rotor is thus "generated" only by the selected harmonic. Harmonics are preferably considered up to a maximum of the 9th order or a maximum of the 7th order.

The understanding of "mainly by the fundamental wave" for the second operating mode is carried out analogously.

Depending on a predetermined machine requirement, the electric machine is controlled with one of the different operating modes during operation. In the present case, activation is generally understood to mean an energization of the winding sets. In this case, the control takes place as a function of the predetermined machine requirement, for example in such a way that the three-phase currents with which the winding sets are applied are changed in their value for setting the different operating modes.

Conveniently, the predetermined machine demand is the torque generated by the magnetic rotating field and applied to the rotor. In the present case, the acting torque is understood to mean, in particular, a torque that accelerates the rotor. This embodiment is based on the idea that the torque acting on the rotor is to be regarded as an essential parameter of the electric machine. In particular, with regard to the design of the electrical machine as a drive machine of a motor vehicle, different torques are retrieved from the machine, for example, in a driving operation, which thus represent different machine requirements. By dependent on the predetermined machine requirement different operating modes, the electric machine is advantageously adaptable to the different torque requirements.

Preferably, the selected harmonic is the harmonic 5 , Okay (also as 5 , Harmonic wave). That is, the torque acting on the rotor is generated by a magnetic rotating field whose course only by the 5 , Harmonics and in particular is independent of the fundamental wave approximated. In other words, it is only with the 5 , Harmonic a magnetic rotating field and thus a torque "generated". The fundamental wave preferably exerts no influence on the course of the magnetic rotating field in this operating mode, its amplitude is therefore preferably zero.

This refinement is based on the idea that a rotational field profile approximated by the fifth harmonic has proven to be suitable for generating a torque. Of particular importance here is that the self-adjusting magnetic rotating field, which is approximated by the fifth harmonic, has a synchronous, that is in the present case, the same circumferential direction as the circumferential direction of the fundamental and thus like the magnetic rotating field. This is a mandatory requirement for using the 5 , Harmonic generated torque acts as an accelerating torque and thus drives the rotor.

In the first operating mode, the electrical machine is operated in the manner of a reluctance machine on the basis of the rotational field profile approximated by the fifth superelevation. Under reluctance machine will generally be a design of a understood electrical machine in which the torque acting on the rotor is generated by the reluctance force. The reluctance describes the magnetic resistance. In operation, the rotor generally "seeks" for a magnetic field dependent position where the magnetic resistance is at a minimum. Due to the rotating field, this point moves circumferentially around the axis of rotation and thus "pulls" the rotor with.

One advantage here is that the electric machine is optimized for efficiency in the first operating mode for lower torques. This operating mode has therefore already been referred to as an efficiency-optimized operating mode. In particular reluctance machines have proven to be suitable. In the present case, lower torques are understood to mean, for example, torques which preferably correspond to one-half and in particular one-third of a maximum torque of the electric machine.

With regard to the prime mover of a motor vehicle, in the present case, the first operating mode is, for example, an operating mode that is set during a journey in which a substantially uniform and low torque is required, for example, at a uniform speed on a motorway. An adjustment of the first operating mode, for example, by the control unit by a suitable energization of the winding sets. In this case, the electric machine can also be operated in the manner of a synchronous machine in the first operating mode.

Preferably, the control unit is set up such that, in operation, the machine is controlled with the first operating mode or the second operating mode as a function of the predetermined machine requirement. Herein, the advantage is seen that the machine can be customized and optimized individually adapted to the given machine requirement and set, resulting in terms of efficiency optimization, for example, to a longer battery life of the electric motor vehicle and thus an improved range.

According to an alternative development, the control unit is set up such that, in operation, the machine is controlled with the third operating mode as a function of the predetermined machine requirement. In this case, an amplitude component of the selected harmonic (in the present case preferably of the fifth harmonic) in the case of a superimposition with the fundamental for approximating the course of the magnetic rotating field is preferably> 25%. in particular, the amplitude component here is> 50% and especially> 75%. The amplitude components> 50% and> 75% in each case represent partial operating modes of the third operating mode.

Of particular importance is that according to a preferred embodiment, the operating modes in response to a user signal during operation of the electric machine, so for example during a journey of the motor vehicle, are interchangeable. That Depending on a torque request occurring during the journey, the electric machine changes, for example, from the first operating mode to the second operating mode. This "change" is preferably carried out by a changing energization of the winding sets by the control unit. Thus, the present signal is preferably understood to mean a signal for an occurring or changing torque request. The user signal is, for example, an electrical signal which is transmitted by control electronics (for example in the case of autonomous driving) of the motor vehicle to the control unit. This takes place, for example, as a function of a change in the profile of the roadway, e.g. when the inclination of the road changes. Alternatively, the user signal is, for example, a change in the accelerator pedal position. As an alternative or in addition, the change of the operating modes is made possible by a manual input of a "change signal" of the driver.

The advantage of this embodiment can be seen in the combination of the modes of action of the machine types already mentioned in the introduction (asynchronous machine and reluctance machine). In this context, operating range-dependent advantages of these types of machines, in particular with regard to the efficiency in a machine are combined. In other words, it is thus a machine request-dependent choice between the operating method of the asynchronous machine (preferably when required high torque) and the operating method of the reluctance machine (preferably with lower torque required) when using only one electric machine solely by a suitable energization of the winding sets by the Control unit and then adjusting magnetic rotary field achieved.

To control, ie for energizing the winding sets, the control unit preferably has a respective converter for a winding set. In the present case, the control unit thus has two converters which are each designed to supply current to each of a set of windings. For this purpose, the inverters are preferably three-phase converters, which are input to a DC intermediate circuit within the motor vehicle or to a battery of the motor vehicle, which to an energy supply for the electric machine is used, are connected. On the output side, the inverters are each connected to the three phases of a winding set.

The inverters are furthermore designed in such a way that a frequency and / or an amplitude of the individual currents of the winding sets are adjusted during operation of the electrical machine in such a way that the rotational field characteristics already approximated by the respective waves are established. The adjustment of the amplitude and / or frequency takes place, for example, via a control with a control signal of semiconductor switching elements within the converter. The control signal is presently provided by the control unit, for example. For this purpose, for example, the respective different current values required for setting a specific operating mode for each phase are stored in the control unit, in particular as a function of the current driving situation, such as the current driving situation. the current load request. That During the driving operation, stored phase current values for controlling the machine are used as a function of the current load request. The determination of the phase current values required for a respective operating mode is carried out, for example, simulation-based with the aid of commercially available programs, especially in the context of the development of such a type of machine. The phase current values determined in this way are then determined e.g. for the respective motor vehicle read into a memory of the control unit.

During operation of the electrical machine, the current actual phase currents are detected. In order to set an operating mode, the phase current values stored for the operating mode concerned are preferably set by the inverters, i. the individual phase is supplied with the corresponding current values. An adjustment of the phase currents takes place, for example, in the manner of a nominal-actual-value comparison, in which a current phase current is detected and adjusted by the respective converter to the required value. So there is a regulation to the desired value.

The adapted energization of the winding sets then sets the desired rotary field course. The control software may also be connected, for example, with the aforementioned control electronics of the motor vehicle to interact with this for the purpose of a change of operating modes and thus a change in the energization of the winding sets.

Alternatively or additionally, the converters, for example the intermediate circuits of the converters, are connected to one another in order to achieve a more precise synchronization of the current flows of the winding sets.

The winding sets are arranged, for example offset by 60 ° to each other, so that the individual windings are distributed uniformly around the circumference. According to a preferred embodiment, however, the two sets of windings are circumferentially arranged offset at an angle of 30 ° to each other on the stator. This discrete winding distribution inherently produces a preferred course of the magnetic rotating field, which can be approximated in particular by the fifth superelevation. In other words, due to the aforementioned winding distribution, a 5.sup.sharp in the rotating field course is generated, which is used in particular for torque generation in accordance with the first operating mode. Thus, it is thereby further allowed on the part of the control unit for adjusting the torque acting on the rotor in the first operating mode to vary the 5.Oberwelle in magnitude (amplitude) and phase.

Preferably, the rotor is designed in the manner of a cage rotor. For this purpose, the rotor has a plurality of circumferentially arranged and extending along the axis of rotation rotor rods. The rotor rods are also arranged spaced apart in the circumferential direction.

In the present case, a squirrel-cage rotor is especially understood to mean a rotor design in which the individual rotor rods are mechanically and preferably electrically connected to each other at the end by means of an annular rotor element. Due to the electrical connection of the squirrel cage rotor is also referred to as squirrel cage, since the individual rotor rods are electrically shorted together by the annular rotor element.

The advantage of this rotor design is that the squirrel cage rotor is the preferred rotor geometry or design for asynchronous machines. This makes it possible to resort to standard components and in particular conventional manufacturing methods for the rotor. Furthermore, this ensures the operation of the electric machine, in particular in the second operating mode, in which the electric machine operates as already mentioned in the manner of an asynchronous machine.

According to an expedient development, the number of rotor bars corresponds to twice the order of one selected harmonic. In the present case, therefore, the rotor preferably has ten rotor bars, since the selected for the first mode of operation harmonic order 5 having.

Due to this design of the rotor is an interaction of the rotor with the through the selected harmonic wave (in this case, the 5.Oberwelle) approximated rotating field in the first operating mode for generating a torque achieved and optimized. The rotor rods furthermore preferably have an electrically conductive, but magnetically poorly conducting material, for example copper.

Further preferably, a magnetically permeable material, for example, a bent steel, is arranged in each case between adjacent rotor rods. The arrangement of the magnetically permeable material serves to optimize the interaction of the rotor, in particular in the first operating mode with the magnetic rotating field approximated by the selected harmonic.

Conveniently, the winding sets are mutually electrically offset by an angle of 30 °. That the three-phase three-phase currents of the two sets of windings are phase-shifted by 30 °. This value results in and through the design of the electrical machine. In other words, in the design of the electrical machine, especially in the design of a required phase shift to achieve a synchronous magnetic rotating field during operation, usually the full electrical angle of 360 ° is divided by twice the number of phases. In the present case, the electrical machine has two sets of windings each with three phases, so in determining the required phase shift, the electrical angle of 360 ° is divided by 12 (2 x number of total phases), resulting in a phase shift of 30 °.

This phase shift also has the advantage that the approximated course of the magnetic rotating field has the desired 5.Oberwelle, which is used to generate a torque. The course of the magnetic rotating field generally approaches better in six-phase machines to a (desired pure) sinusoidal course, as for example in a three-phase machine.

According to a preferred embodiment, the three-phase winding sets are each connected according to a star connection. In the present case, star connection is understood to mean that the three phases of a respective winding set are electrically connected to one another at one end. At the respective other end, the three phases of the winding sets are connected to one phase each of the control unit, in particular of the converter. Thus, each phase of a winding set is connected to one phase of the three-phase network.

The advantage of this embodiment is that within the interconnected winding sets the sum of all occurring currents is zero and no harmonics occur whose order is a multiple of the number 3 correspond. For this reason, none occurs in the approximate rotary field course 3 , Harmonic on. In the present case, the star point is generally understood to mean the point in the interconnection of a winding set at which the three phases are connected to one another by electrical means.

In a preferred embodiment, the three-phase winding sets each have a floating star point. That in particular, the neutral point is not connected to, for example, a ground potential. This embodiment is made possible by the mutually canceling currents within the neutral point.

As a result, the production and Verschaltungsaufwand the electrical machine is significantly reduced.

According to an expedient embodiment, the electric machine is arranged in a motor vehicle and serves here, as already mentioned as an electric drive motor. The motor vehicle here is designed either as a plug-in hybrid vehicle (internal combustion engine and electric motor) or as a motor vehicle driven purely by electric motor.

• 1 einen grob skizzierten Querschnitt einer sechsphasigen elektrischen Maschine,
• 2 eine grob skizzierte Verschaltung der sechsphasigen elektrischen Maschine an eine Steuereinheit,
• 3 eine grob skizzierte perspektivische Darstellung eines Rotors,
• 4 der skizzierte Verlauf des magnetischen Drehfeldes im ersten Betriebsmodus,
• 5 der skizzierte Verlauf des magnetischen Drehfeldes im zweiten Betriebsmodus sowie
• 6 der skizzierte Verlauf des magnetischen Drehfeldes im dritten Betriebsmodus.

Embodiments of the invention will be explained in more detail with reference to FIGS. These show in partly strongly simplified representations:

• 1 a roughly sketched cross-section of a six-phase electric machine,
• 2 a roughly sketched interconnection of the six-phase electrical machine to a control unit,
• 3 a roughly sketched perspective view of a rotor,
• 4 the sketched course of the magnetic rotating field in the first operating mode,
• 5 the sketched course of the magnetic rotating field in the second operating mode and
• 6 the sketched course of the magnetic rotating field in the third operating mode.

In the figures, like-acting parts are represented by the same reference numerals.

1 shows a cross-sectional view of an electrical machine 2 , In the embodiment, the electric machine 2 as a six-phase electric machine 2 and in particular designed as a drive machine for a motor vehicle, not shown here. The electric machine 2 has an annular stator 4 as well as one annular rotor 6 on. The rotor 6 is about a rotation axis R arranged and rotatable about this. The stator 4 is surrounding the rotor 6 concentric around the circumference.

At the stator 4 are six stator poles 8th formed, each having a stator winding 10 have and are circumferentially spaced from each other. Three stator windings each form a winding set 12a B. Thus, the electric machine points 2 in the exemplary embodiment two winding sets 12a , b on. In the exemplary embodiment, the two winding sets 12a , B circumferentially spaced at an angle of 30 ° from each other. In other words: the second winding set 12b is about 30 ° in the circumferential direction with respect to the first winding set 12a postponed. There 1 For the sake of simplicity, the true winding distribution is not drawn to scale for the sake of simplicity of construction of such a six-phase electric machine.

Between the rotor 6 and the stator 4 is in a radial direction 5 looks at an air gap 14 formed, in which in the operation of the electric machine 2 a magnetic rotating field B (see Fig. 4ff) is formed, which for generating a on the rotor 6 acting torque M serves. In particular, it is in the present electrical machine 2 around an asynchronous machine.

The two winding sets 12a , b are in operation each with a three-phase current l ~ applied.

A possible interconnection of the electrical machine 2 for loading with the three-phase three-phase current I ~ is in 2 shown.

The electric machine 2 is in for reasons of simplification 2 merely representative by the two winding sets 12a , b, so by six coils 16a-f represented in the manner of an equivalent circuit diagram. The arrangement of the winding sets 12a, b in 2 corresponds to the actual, in 1 for reasons of simplicity not shown arrangement of the winding sets 12a, b inside the electric machine 2 ,

All in relation to the winding sets 12a, b and in relation to the six coils 16a-f The following explanations apply to the electrical machine 2 and vice versa.

The two winding sets 12a, b are in the embodiment each in the manner of a star connection 18 connected. The three stator windings 10 a respective winding set 12a, b thus have a common star point 20a, b , In the embodiment, a potential-free star point 20a , b on. That is, the three stator windings 10 a respective winding set 12a, b in each star point 20a , b are electrically interconnected and the neutral point 20a , b is in particular not connected to an electrical potential. This embodiment is based on the consideration that within the stator windings 10 occurring currents in the neutral point 20 cancel each other out. Thus, there is no connection of the star point 20 For example, to an outflow of the currents to a ground potential necessary. Furthermore, the two star points 20a , b isolated in the embodiment to each other.

For loading the winding sets 12a , b with the already mentioned three-phase current l ~ are the winding sets 12a , b to a control unit 22 connected. The control unit 22 is adapted to the amplitude of the three-phase currents, ie the current values of the respective phases U1 . V1 . W1 to regulate the three-phase currents. The control unit has for this purpose each a three-phase inverter 24a , b for a winding set 12a, b on. One phase each U1 . V1 . W1 (or. U2 . V2 . W2 for the second inverter 24b) of the inverter 24a is at one end of a coil 16a-f connected. In the embodiment, therefore, the coils 16a, c, e (first winding set 12a) to the first inverter 24a and the coils 16b, d, f (second winding set 12b) to the second inverter 24b connected.

To a particular synchronous field distribution within the air gap 14 the electric machine 2 to reach, are the two winding sets 12a , b by a phase shift Δφ with a value of 30 ° shifted electrically.

In 3 is a sketched perspective view of the rotor 6 the electric machine 2 shown. The rotor 6 is designed as a squirrel cage rotor and has several, in the exemplary embodiment ten, rotor rods 26 on. The rotor bars 26 are arranged uniformly circumferentially and extend along the axis of rotation R , Each end has the rotor 6 a short-circuit ring 28 on, the rotor bars 26 Short-circuiting with each other electrically. Due to this, the present rotor becomes 6 also referred to as squirrel cage rotor.

The rotor bars 26 have an electrically conductive material, such as copper. Between adjacent rotor bars 26 In each case, a magnetically permeable material, for example, bent steel is arranged. Through this material composition is an interaction of the rotor 6 with the magnetic rotating field B (see Fig. 4ff) optimized.

The following is based on the description of 4 to 6 received on individual operating modes of the electric machine, which by the control unit 22 Can be "adjusted". Since the description has previously dealt in detail with the machine-typical properties and consequences of the operating modes (in particular with regard to operation in the manner of an asynchronous machine or in the manner of a reluctance machine as a function of the operating modes), the following explanation is rather a graphic explanation for a more detailed understanding of the approximation of the magnetic rotating field B ,

In 4 is the course of the magnetic rotating field B depending on a circumferential angle α shown. The circumferential angle α in this case describes a position in the circumferential direction about the axis of rotation R , For example, a circumferential angle with the value π (corresponds to an angular extent of 180 °) corresponds to half a revolution of the magnetic rotating field B starting from a reference position. A circumferential angle α with the value of 2π thus corresponds to a complete revolution of the magnetic rotating field B 360 ° from the reference position.

As already explained in the context of this application, the course of the magnetic rotating field B using a Fourier analysis mathematically in a superposition (also referred to as approximation) of a sinusoidal fundamental wave G and at least one selected sinusoidal harmonic OW , This approximation serves, for example, as a basis for setting the amplitudes of the three-phase currents with which the winding sets 12a, b in operation by the control unit 22 be charged.

The in 4 The course represented represents the magnetic rotating field B , as it sets in a first operating mode. In the first operating mode, the course of the magnetic rotating field is mainly by a selected harmonic, in the embodiment, the harmonic 5 , order OW ₅ approximated. The value and thus the influence of the fundamental GW for approximation of the rotating field course B is zero here. Thus, it is possible, alone with that through the 5.Oberwelle OW ₅ adjusting rotating magnetic field B to generate a torque and thus the rotor 6 drive. In this operating mode, the electric machine is especially for torques M with a value of, for example, up to one third of the maximum torque efficiency optimized.

In 5 is the course of the magnetic rotating field B when energizing the winding sets 12a, b represented according to the second operating mode.

Here is the course of the magnetic rotating field B mainly by the fundamental wave GW approximated. In other words, it only becomes the fundamental GW a torque M generated. The influence of the selected harmonic, in this case the 5 , harmonic OW ₅ is zero here.

In the operating mode according to 5 The machine "works" in the manner of an asynchronous machine and is therefore optimized for efficiency, especially for high torque values (two-thirds of the maximum torque and higher).

In 6 is the course of the magnetic rotating field B shown in the third mode of operation. Here is the course of the magnetic rotating field B by a superposition of the fundamental wave GW with the selected 5th harmonic OW ₅ approximated. This operating mode represents, for example, a kind of intermediate mode between the two aforementioned operating modes. That is, in this operating mode, both the fundamental and the fifth harmonic influence and contribute to the approximation of the course of the magnetic rotating field B exercise. Here, the proportion of the fundamental wave GW at the superimposition in particular ≥ 50%.

The superposition of the fundamental wave GW with the 5th harmonic results in a superposition wave UW , which follow the step-like (actual) course of the magnetic rotating field B approaches.

In the 4 to 6 is the approximation of the course through the sinusoidal fundamental wave GW as well as the selected 5th harmonic. That is, the waves alone and a superposition of the waves (see. 6 ) approach the step-like (actual) course of the rotating magnetic field B Due to the mathematical writability of a design and control (energization) of the winding sets 12a , b are used; especially with regard to the aforementioned operating modes.

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

LIST OF REFERENCE NUMBERS

2

electric machine

4

stator

5

radial direction

6

rotor

8th

stator

10

stator

12a, b

winding sets

14

air gap

16a-f

Do the washing up

18

star connection

20

star point

22

control unit

24a, b

inverter

26

rotor bars

28

Shorting ring

α

circumferential angle

Δφ

electrical phase offset

B

magnetic rotating field

l ~

Three-phase

M

torque

R

axis of rotation

U1, V1, W1

Phases of the first inverter

U2, V2, W2

Phases of the second inverter

GW

sinusoidal fundamental

OW

sinusoidal harmonic

OW ₅

harmonic 5 , order

UW

Superposition wave

Claims (15)

Electric machine (2), in particular electric drive machine for a motor vehicle, comprising: an annular rotor (6) formed around a rotation axis (R) and rotatable about the rotation axis (R), - An annular stator (4) which is arranged around the rotation axis (R) such that it surrounds the rotor (6) circumferentially concentric, such that in a radial direction (5) viewed between the rotor (6) and the stator ( 4), an air gap (14) is formed, wherein the stator (4) has two three-phase, in operation controllable winding sets (12a, b) and - A control unit (22) which is set up and designed such that during operation of the control unit (22) to a control of the electric machine (2) the winding sets (12 a, b) are subjected to a three-phase current (l ~) and thereby sets a magnetic rotating field (B) in the air gap (14) for generating a force acting on the rotor (6) torque (M), wherein the course of the magnetic rotating field (B) can be approximated by a superposition of a sinusoidal fundamental wave (GW) with sinusoidal harmonics (OW), - The control unit (22) for controlling the electric machine (2) is formed in different operating modes, namely in one first operating mode, in which the rotating magnetic field (B) that arises is mainly approximated by a selected harmonic (OW), second operating mode, in which the rotating magnetic field (B) that arises is mainly approximated by the fundamental wave (GW), third operating mode, in which the adjusting magnetic rotating field (B) by approximating the fundamental wave (GW) with the selected harmonic wave (OW) is approximated, wherein depending on a predetermined machine requirement during operation, the electric machine (2) is driven with one of these operating modes becomes. Electric machine (2) according to the preceding claim, wherein the predetermined machine requirement is the generated torque (M) acting on the rotor (6). Electric machine (2) according to one of the two preceding claims, wherein the selected harmonic (OW) is the 5th harmonic wave (OW ₅ ). Electrical machine (2) according to one of the preceding claims, wherein the control unit (22) is set up such that, in operation, the electric machine (2) is controlled with the first operating mode or the second operating mode as a function of the predetermined machine requirement. Electric machine (2) after a Claims 1 to 3 , wherein the control unit is set up such that, in operation, the electric machine (2) is controlled with the third operating mode as a function of the predetermined machine requirement, an amplitude component of the selected harmonic (OW) being superimposed on the fundamental wave (GW) to approximate the Course of the magnetic rotating field (B)> 25%. Electric machine (2) according to one of the preceding claims, wherein the operating modes are exchangeable in operation as a function of a user signal. Electric machine (2) according to one of the preceding claims, wherein the two sets of windings (12a, b) are arranged offset by an angle of 30 ° to each other on the stator (4). Electric machine (2) according to one of the preceding claims, wherein the rotor (6) is designed in the manner of a squirrel-cage rotor and for this purpose Having a plurality of circumferentially arranged and along the rotation axis (R) extending and spaced apart rotor rods (26). Electric machine (2) according to the preceding claim, wherein the number of rotor bars (26) corresponds to twice the order of the at least one selected harmonic (OW), preferably 10. Electric machine (2) according to one of the preceding claims, wherein in each case a magnetically permeable material is arranged between adjacent rotor bars (26). Electric machine (2) according to one of the preceding claims, wherein the winding sets (12a, b) are mutually offset by 30 ° electrically. Electric machine (2) according to one of the preceding claims, wherein the winding sets (12a, b) are each connected according to a star connection (18). Electric machine (2) according to the preceding claim, wherein the winding sets (12a, b) each have a floating star point (20). Motor vehicle with an electric machine (2) according to one of the preceding claims. Method for operating an electric machine (2), in particular an electric drive machine for a motor vehicle, comprising: an annular rotor (6) formed around a rotation axis (R) and rotatable about the rotation axis (R), - An annular stator (4) which is arranged around the rotation axis (R) such that it surrounds the rotor (6) circumferentially concentric, such that in a radial direction (5) viewed between the rotor (6) and the stator ( 4) an air gap (14) is formed, wherein the stator (4) has two three-phase, controllable in operation winding sets (12a, b) and the winding sets (12a, b) are subjected to a three-phase current (l ~) and thereby a magnetic rotating field (B) in the air gap (14) adjusts to generate a force acting on the rotor (6) torque (M), wherein the course of the magnetic rotating field (B) can be approximated by a superposition of a sinusoidal fundamental wave (GW) with sinusoidal harmonics (OW), - For driving the electric machine (2) different modes of operation are provided, namely a first operating mode in which the adjusting magnetic rotating field (B) is mainly approximated by a selected harmonic (OW), second mode of operation, in which the rotating magnetic field (B) which arises is mainly approximated by the fundamental wave (GW), third mode of operation, in which the self-adjusting magnetic field (B) is approximated by a superposition of the fundamental wave (GW) with the selected harmonic wave (OW), wherein the electrical machine (2) is controlled with one of these operating modes in response to a predetermined machine requirement.

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