Circuit for an electric motor

Abstract

A circuit (1) for an electric motor (2), wherein the electric motor (2) comprises at least one stator (3) with at least three coils (4, 5, 6) and a rotor (7) with at least two magnetic poles (8, 9); wherein the electric motor (2) can be operated by the circuit (1) at least in two states (10, 11): a) in a first state (10), the coils (4, 5, 6) can be loaded with different currents of a three-phase alternating current system (12), respectively, and the rotor (7) can be set in rotation around an axis of rotation (13); b) in a second state (11), the coils (4, 5, 6) can be loaded with a same-phase alternating current (14).

Description

TECHNICAL FIELD

[0001] The invention relates to a circuit for an electric motor. The electric motor comprises at least one stator and a rotor. In particular, the electric motor is an axial flux motor (AFM). BACKGROUND

[0002] Applications are known in which, in addition to the drive power of the electric motor, the heating power of the electric motor can also be used. For example, when conveying a urea solution (e.g. Ad-blue) used for exhaust gas treatment, it can be desirable to heat the urea solution. The electric motor used to drive the pump also generates heat, which can be used, for example, to thaw the urea solution.

[0003] From WO 2019 / 170738 A1 a method for operating an electric motor is known, which can be operated in at least two states. In a first state, the coils are operated with respectively different currents of a three-phase alternating system and the rotor is set in rotation about a rotation axis. In a second state, the coils are operated with a phase-locked alternating current. The phase-locked alternating current used in the second state makes it possible, for example, to heat components of the housing of the electric motor selectively.

[0004] Usually two different and separately implemented or independently operable circuits are used to generate the two states. This is considered necessary in order to meet different requirements in relation to the voltage and frequency provided.

[0005] Here, for the first state, a low-frequency rotating field of, for example, less than 1,000 Hz [Hertz] is generated between the potential connections of the circuit. For the second state, it is necessary to generate a high-frequency phase-locked alternating current of, for example, at least 5 kHz between the potential connections. SUMMARY

[0006] On the basis thereof, it is the task of the present invention to at least alleviate or even solve the problems outlined with reference to the prior art. In particular, a circuit should be proposed with which the electric motor can be operated selectively to generate heating power.

[0007] In order to solve these tasks, a circuit according to the features of patent claim 1 is proposed. Advantageous refinements are the subject of the dependent patent claims. The features mentioned in the patent claims individually can be combined with one another in a technically meaningful manner and can be supplemented by elucidating facts from the description and by details from the figures, in which further embodiments of the invention are indicated.

[0008] A circuit for an electric motor is proposed, wherein the electric motor comprises at least one first stator with at least three (or a multiple of three) coils and a rotor with at least two magnetic poles. The electric motor is at least operable in two states by means of the circuit:

[0009] a) In a first state, the coils are able to be loaded with different (electrical) currents of a three-phase alternating system (i.e. each current is offset by a phase angle from one another), and the rotor is able to be placed in rotation around an axis of rotation;

[0010] b) In a second state, the coils are able to be loaded with in-phase alternating current.

[0011] The circuit has at least one first potential connection and a second potential connection, which are connectable or connected with different potentials (for example positive and ground) of a direct voltage source. The circuit comprises three half-bridges between the potential connections, wherein each coil is conductively connectable or conductively connected via a respective first connection with a respective half-bridge and via a respective second connection with the other coils. The circuit has a fourth half-bridge between the potential connections, which is conductively connectable or conductively connected with a star point connecting the second connections.

[0012] In particular, the electric motor can also be operated as a generator. The statements regarding the electric motor apply accordingly to the operation as a generator.

[0013] In particular, the stator and the rotor are arranged adjoiningly and coaxially to one another along an axial direction. The coils are arranged adjoiningly along a circumferential direction (on a common diameter). Thereby, in particular an axial flux electric motor is configured, wherein the magnetic flux between the coils and the magnetic poles extends parallel to the axis of rotation along the axial direction. However, in particular other configurations of the electric motor are possible and can be used in combination with the circuit.

[0014] In particular, the electric motor is a BLDC, i.e. a brushless direct current electric motor, wherein the fixed stator comprises the coils and the rotatable rotor comprises permanent magnets.

[0015] In particular, the power consumption of the electric motor in the second state (temporarily or for a predefinable period of time) is only for heating the body. In particular, the body is arranged spaced apart from the stator and the rotor.

[0016] In addition, the power consumption of the circuit (temporarily or for a predefinable period of time) can additionally or also only be for driving the rotor, so that the rotor rotates around the axis of rotation with a rotational speed of more than zero ("0") revolutions per minute.

[0017] In the second state, the body should or can be heated, in particular by means of induction. For example, the body can form a housing of the electric motor (or a part thereof). The body can form a line for a fluid, so that the fluid can be heated via the body. For example, the body can be a shaft. For example, a pump device can be heated via the shaft, which is an integral part of the pump device. Thus, for example, a fluid to be conveyed by the pump device can be heated via the shaft.

[0018] When heated by induction, heat is formed directly in the body itself, so that it does not have to be transferred by thermal conduction. The heating power can be well controlled. In order to heat inductively, a high-frequency (homophasic) alternating current is generated by an electric circuit and applied to the stator, or an alternating magnetic field is generated in the coils of the stator, which generates eddy currents in the material of the body. Inductive heating can also take place through non-conductive materials (e.g. walls, housings, etc.). The environment is only indirectly heated (in particular due to thermal radiation or thermal conduction from the body heated inductively).

[0019] The stator of the electric motor has, in particular, a soft magnetic material, for example a so-called "soft magnetic composite" (SMC), or a combination of electrical steel sheets and SMC. The coils of the stator comprise a core, which is preferably manufactured in a press and bake manner from soft magnetic material. The SMC material is not sintered in this case. Rather, the temperature is controlled below the melting temperature, which is however sufficient so that the core permanently retains its geometry.

[0020] In particular, the rotor has permanent magnets and / or soft magnetic elements or poles, for example in recesses. Permanent magnet-excited synchronous or brushless direct current electric motors (abbreviation BLDC) can preferably be constructed with permanent magnets, while reluctance electric motors as electric motors can for example be created with soft magnetic elements.

[0021] Further details, in particular regarding the structure of the stator and also the rotor, are known, for example, from WO 2016 / 066714 A1, in particular in the case of the use of SMC.

[0022] In particular, the electric motor has an electrical power consumption (i.e. maximum drive power) for the first state of less than 1,000 watts (nominal power), preferably less than 500 watts, particularly preferably less than 100 watts.

[0023] In particular, the power consumption of the electric motor is used on the one hand for driving the rotor (first state), so that the rotor rotates about the axis of rotation at a rotational speed of more than "0" revolutions per minute. On the other hand, the power consumption of the electric motor is used for heating the body (second state).

[0024] In particular, the electric motor can be operated in two states by the circuit, such that in the first state the rotor is driven by operating the electric motor and in the second state the body is warmed up by operating the electric motor in time parallel.

[0025] In time parallel here means in particular that between the first state and the second state is changed within a time interval (for example one second) (in particular always back and forth), if necessary for different long sub-intervals of the time interval.

[0026] The heating power delivered to the body is in particular the electrical power [in watts] provided by the circuit during operation in the second state.

[0027] Preferably, in the second state (virtually) no electrical power is used to drive the rotor. In particular, the rotational speed of the rotor is therefore "0" revolutions per minute, despite the power consumption of the electric motor.

[0028] In particular, the electric motor is not accelerated in the second state. This means in particular that there can be a rotational speed of the rotor greater than zero revolutions per minute, but the rotor is not accelerated by the electrical power used only for converting into heat.

[0029] A common circuit for driving an electric motor often comprises a first potential connection and a second potential connection, which can be connected with different potentials (for example positive and ground) of a direct voltage source, wherein between the potential connections three half-bridges are arranged, wherein each coil of the electric motor can be electrically conductively connected via a respective first connection with a respective half-bridge and via a respective second connection with the other coils.

[0030] The three half-bridges of the circuit enable the generation of a three-phase alternating system or a multiphase rectangular current, wherein the phases are offset by 120 degrees from each other. Each current or phase current is delivered to or injected into the coils via the first connections. The coils are connected to each other via the second connections, wherein the different phase currents cancel each other out in the star point, so that no separate or additional return line to the respective other potential connection is required.

[0031] In particular, the half-bridges comprise a device of upper and lower transistors in a known manner, via which the potential connections are connected to each other. In particular, a diode is connected in parallel to each transistor.

[0032] The known circuit is only slightly enlarged by the supplement of only one further half-bridge and by its connection to the star point. However, here this fourth half-bridge and its advantageous arrangement already enable the additional implementation of the second state.

[0033] In particular, each half-bridge has at least one upper transistor (high-side transistor) and a lower transistor (low-side transistor), which are conductively connected to one another. The upper transistor is conductively connected to the first potential line and the lower transistor is conductively connected to the second potential line. Each half-bridge has a contact device between the upper transistor and the lower transistor, via which one line each can be connected to the respective half-bridge.

[0034] The first lines each arranged, for example, at the electric motor are thus conductively connected via the contact devices to one of the first, second or third half-bridges, for example. The second line or star point arranged, for example, at the electric motor is connected via the contact device to the fourth half-bridge.

[0035] In particular, in order to generate the second state, the circuit can be operated such that, on the one hand (in the first circuit state), the upper transistors of the first, second and third half-bridges synchronously (i.e. in time parallel) conductively connect the first potential line to the respective first line, while the lower transistors of these half-bridges electrically separate the respective first line from the second potential line. The lower transistor of the fourth half-bridge synchronously therewith conductively connects the second line to the second potential line. On the other hand (in the second circuit state), the lower transistors of the first, second and third half-bridges synchronously conductively connect the second potential line to the respective first line, while the upper transistors of these half-bridges electrically separate the respective first line from the first potential line. The upper transistor of the fourth half-bridge synchronously therewith conductively connects the second line to the first potential line. Thus, if a homophasal current is to be present in the heating operation (second state), all first lines are at the same potential. In this case, a potential difference can only be generated by adding an additional return line, here also by the fourth half-bridge.

[0036] In particular, these circuit states are implemented in time succession.

[0037] In these circuit states of the second state, the star point is conductively connected via the fourth half-bridge to the potential line each, such that in both circuit states a potential difference is present at each coil. Since the upper transistors or the lower transistors of the first, second and third half-bridges are switched simultaneously and in the same way, there is only a single-phase current. An alternating current is generated by the changeover between the circuit states.

[0038] In particular, the circuit comprises at least one capacitor via which the star point can be connected to the fourth half-bridge. In the operation of the electric motor, the capacitor is arranged between the star point and the fourth half-bridge.

[0039] The at least one capacitor is in particular arranged in a series circuit between the electric motor and the fourth half-bridge.

[0040] Alternatively, at least one capacitor is arranged in parallel circuit between the first and the second connection. In particular, one or more compensation capacitors are connected in parallel to each phase, in particular between the first and the second connection of one coil or a plurality of coils connected to form a phase. Here, it should be noted that if the PWM signal used for generating the current shape in the first state has a frequency similar to the heating frequency, the current smoothing effect of the motor inductance is disabled and a targeted current shape generation is thus no longer possible. To avoid this problem, the PWM frequency and the heating frequency should be far away from each other.

[0041] In particular, the capacitance of the at least one capacitor is selected in dependence on the inductance of the coil of the motor such that the reactive power can be at least partially compensated when the motor is operated.

[0042] Without the at least one capacitor, the heating power that can be generated would be able to be realized only limitedly, in particular in the case of low-voltage systems, for example in automotive applications, since the coil current is limited at high frequencies of the alternating current due to the high impedance of the coil. Here, the impedance of the coil increases in proportion to the frequency according to Z = j2πfL, wherein

[0043] Z: Impedance of the coil

[0044] j: Imaginary unit

[0045] f: Frequency of the alternating current

[0046] L: Inductance of the coil.

[0047] Since the connection potential of the circuit is connected to a direct voltage source, in the generator operation then to a sink, a correspondingly high voltage must be provided through the circuit. However, this is not realizable in automotive applications with low on-board network voltage, in particular. The reactive power compensation can be achieved by reaching a resonance state by means of the arrangement of at least one capacitor, in particular. In this case, the required voltage between the potential connections can also be generated with a significantly lower direct voltage.

[0048] The branch voltage falling over the coil of the motor can generally be determined by multiplying the coil impedance by the phase current:

[0049] U = Z · I

[0050] Here, the coil impedance can always be described by a real part independent of the frequency and a complex part dependent on the frequency. In consideration of parasitic components and other frequency-dependent effects or loss mechanisms, a complex relationship between the current and the voltage results. However, the impedance can be represented in a well-approximated manner as a simplified relationship for two states. In a first state, the ohmic wire winding resistance of the coil branch constitutes the real part of the impedance, while the inductive behavior can be expressed by the imaginary part of the impedance. The branch voltage (voltage between the first and the second connection, i.e. the voltage falling across the coil) can be calculated for this first state by means of the following equation:

[0051] U I i + j2πfL i , wherein

[0052] U : branch voltage, i.e. voltage between the potential connection electrically connected via the first connection and the second connection, respectively

[0053] I : current loaded to the motor

[0054] R i : resistance of the respective coil or current path running through the coil

[0055] j: imaginary unit

[0056] f: frequency of the alternating current

[0057] L i : inductance of the respective coil

[0058] For the second state, this description of the coil impedance is, however, not sufficient, among other things. The iron losses occurring in the body should be considered more precisely. The coil or the magnetic circuit becomes lossy, so that an additional component can be defined in the real part, to which the active power loss occurring in the body can be traced back. Due to the in-phase behavior, the motor branch can be regarded as a parallel circuit in this state, so that the branch voltage can be expressed in a well-approximated manner for the second state by means of the following equation:

[0059]

[0060] R v : resistance for describing the loss component in the second state

[0061] The arrangement of at least one capacitor changes the above-listed equations as follows:

[0062]

[0063] ​​​​C: capacitance of the at least one capacitor

[0064] Here, the capacitance of the at least one capacitor should be chosen such that it is applicable that:

[0065]

[0066] Thus, it is possible, inter alia, to completely compensate the imaginary part and the frequency-dependent component, and it is possible to strongly reduce the voltage requirement, such that it is applicable that:

[0067]

[0068] Due to the high branch voltage of the electric motor, i.e. the voltage between the first and the second connection, a sufficiently high dielectric strength and as low as possible ESR (equivalent series resistance) should be considered in determining the size of the at least one capacitor in order to reduce the compensation losses. Since, for example, the capacitor experiences a change in its capacitance depending on the temperature, and the core of the coil can also behave in relation to the temperature, it is possible to ensure a frequency stability depending on the temperature. If the resonance state is detuned, i.e. the capacitance changes, for example, with the temperature, a different frequency is required in order to maximize the loss power. In this case, the frequency can be readjusted via a control unit, for example a microprocessor. The measurement of the current, for example by means of a shunt resistor (typically a low-side shunt), can be used in order to maximize the current and thus the losses. Thus, it is possible, inter alia, to measure the current and to adapt the frequency alternately, wherein these steps can be repeated several times.

[0069] Furthermore, a method for operating an electric motor with the described circuit is proposed. In order to generate the first state, the electric motor is operated exclusively via the first, the second and the third half-bridge.

[0070] In particular, during the first state, the star point is electrically conductively connected to only one potential connection or (electrically) separated from both potential connections (i.e. arranged in a floating manner) via the fourth half-bridge.

[0071] In particular, each half-bridge has at least one upper transistor and a lower transistor, which are electrically conductively connected to one another; wherein the upper transistor is electrically conductively connected to the first potential connection and the lower transistor is electrically conductively connected to the second potential connection. Each half-bridge has a contact device between the upper transistor and the lower transistor, via which one connection is connected to the respective half-bridge. In order to generate the second state:

[0072] - in one aspect, the upper transistors of the first, second and third half-bridges are switched synchronously and conductively connect the first potential line with the respective first line, while the lower transistors of these half-bridges, which are switched synchronously and conductively, separate the respective first line from the second potential line; wherein the lower transistor of the fourth half-bridge is switched synchronously for connecting the second line with the second potential line; and

[0073] - in another aspect, the lower transistors of the first, second and third half-bridges are switched synchronously and conductively connect the second potential line with the respective first line, while the upper transistors of these half-bridges, which are switched synchronously and conductively, separate the respective first line from the first potential line; wherein the upper transistor of the fourth half-bridge is switched synchronously for connecting the second line with the first potential line.

[0074] The three-phase AC system in the first state is generated in a known manner by controlled switching of the first, second and third half-bridges.

[0075] In particular, the first frequency of the three-phase system has at most 50%, preferably at most 10%, particularly preferably at most 2%, of the second frequency of the AC voltage.

[0076] The first frequency of the three-phase system, i.e. the number of cycles of the phases of the three-phase system per second, is in particular at most 1,000 Hz, in particular at most 500 Hz.

[0077] The second frequency of the AC voltage, in which there are two potential changes per cycle, is in particular at least 5 kHz, preferably at least 10 kHz, particularly preferably at least 15 kHz.

[0078] The maximum heating power that can be generated by the circuit in the second state is in particular at least 50%, preferably at least 100%, particularly preferably at least 200%, of the drive power that can be generated by the circuit in the first state.

[0079] In particular, the maximum heating power that can be generated by the circuit in the second state is at least five times, preferably at least 10 times, particularly preferably at least 25 times or even at least 45 times the drive power that can be generated by the circuit in the first state.

[0080] Thus, if the electrical power consumption, i.e. the maximum drive power, for the first state is up to 1,000 watts (nominal power), the power consumption for the second state can be at least up to 5 kW [kilowatt], 10 kW, 25 kW or even 45 kW.

[0081] In particular, the circuit is operated in different time intervals from one another either for generating the first state or for generating the second state.

[0082] In particular, the transition between the time intervals takes place at a third frequency which exceeds one ("1") Hz, in particular exceeds 5 Hz, preferably exceeds 20 Hz and particularly preferably exceeds 100 Hz.

[0083] In particular, the time intervals assigned to the respective states can be different long. In particular, the first time interval in which the electric motor is operated in the first state is longer, for example at least 10%, at least 20% or at least 40% longer than the second time interval in which the electric motor is operated in the second state.

[0084] In particular, the time component in which the electric motor is operated in the first state or in the second state can thus be implemented differently.

[0085] In particular, the first time interval and / or the second time interval can be different long.

[0086] In particular, different electrical powers can be provided in the different first and / or second time intervals.

[0087] In particular, different electrical parameters, for example frequency, current, etc., can exist in the different first and / or second time intervals.

[0088] Furthermore, an electric motor arrangement is proposed, comprising at least an electric motor, the electric motor comprising at least one stator with at least three coils and a rotor with at least two magnetic poles; the described circuit; and a control device for operating the circuit such that the electric motor can be operated with the described method.

[0089] In particular, the control device is equipped, configured or programmed such that the circuit can be operated according to the described method.

[0090] Preferably, an electrically conductive body is arranged at least within or outside the stator in the radial direction, which electrically conductive body is heated by induction when the electric motor is operated at least in the second state.

[0091] Alternatively or additionally, the body can be the rotor. For this purpose, the rotor has, in addition to the magnetic poles, a carrier material which is referred to as the body.

[0092] In particular, a first specific resistance [Ohm*mm 2 / m] of the body is lower than a second specific resistance of a core of the coil.

[0093] In particular, the SMC material used for the core has a high specific resistance. In particular, the body, for example made of steel, has a lower specific resistance (compared to the material used for the core).

[0094] In particular, the body serves exactly for converting the electrical power provided in the second state into heat. The body preferably has a high electrical and / or magnetic conductivity or is embodied iron-containing, so that an effective heating up is possible. In particular, the core of the coil has a much lower electrical conductivity than the body, so that eddy currents in the core are suppressed. In view of the magnetic conductivity, the body and the core can in particular be embodied identically or similarly.

[0095] In particular, the first specific resistance is at least a half, preferably at least a fifth, particularly preferably at least a tenth, of the second specific resistance.

[0096] In particular, each coil of the stator has a core, which extends from the first end of the at least one stator towards the second end, in particular parallel to the axial direction, wherein the rotor is arranged adjacent to the at least one second end.

[0097] The body in particular extends completely along the circumference (in the radial direction within or outside the core or coil) and along the axial direction (and the rotation axis extending parallel thereto) up to the at least one first end of the core.

[0098] The body preferably contacts the core of the coil at the at least one first end.

[0099] In particular, the magnetic flux is conducted through the body, so that as high a component of the electrical power of the electric motor as possible can be converted into heat by the body.

[0100] In particular, the body extends from the end face of the rotor facing away from the first stator along the axial direction and in the radial direction within or outside the coil up to the first end.

[0101] In particular, the body extends at the at least one first end along the radial direction at least beyond the extension of the core.

[0102] In particular, the body extends at the second end along the radial direction and along the end face of the rotor facing away from the first stator at least beyond the extension of the core (in Flucht).

[0103] In particular, a pump for conveying a fluid can be driven by the electric motor, wherein the pump is operated in the first state (for conveying a fluid) and in the second state at least the fluid conveyable by the pump is heated.

[0104] In the second state, the coil is operated with a phase-locked alternating current. In particular, no multiphase current is present then, so that no driving of the rotor takes place. By the alternating current, an alternating magnetic field is generated, which can generate heat in the body by induction.

[0105] The statements regarding the circuit apply equally to the method and the electric motor device, and vice versa.

[0106] It is therefore proposed that a circuit is used with which electrical power for an electric motor is used on the one hand for driving a rotor, i.e. for performing a rotational movement, and on the other hand for heating a body by means of induction in a targeted manner. Here, it is also possible to heat the body alone without driving the rotor at all. This is particularly advantageous for fluids which can freeze, such as urea water solutions, which have a freezing point at approximately -11 degrees Celsius. The liquid stored in the tank can thus be thawed by the body on the one hand and then be delivered to an increased extent.

[0107] The indefinite articles ("a", "an", and "the") and the terms "comprising", "having" and "including" are used herein for the purpose of clarity and brevity, and should not be construed as limiting. Accordingly, the terms "comprising", "having" and "including" should not be interpreted as meaning only comprising, having or including, but rather should be interpreted as meaning "comprising, having or including at least the recited features, and any additional features".

[0108] It is preventively noted that the numerical terms ("first", "second",...) used here are preferentially (only) used to distinguish a plurality of similar objects, parameters or processes, i.e. in particular do not necessarily predefine a correlation and / or an order of these objects, parameters or processes to each other. If a correlation and / or an order should be intended, this is explicitly stated here or is apparent to the person skilled in the art when studying the specifically described design. As long as a component can occur multiple times ("at least one"), a description of one of the components can equally apply to all or a part of the multiple of these components, but this is not mandatory. BRIEF DESCRIPTION OF DRAWINGS

[0109] The present application and the technical background are explained in more detail below with reference to the drawings. It should be noted that the present application should not be restricted to the listed embodiments.

[0110] In particular, as long as not explicitly described otherwise, it is possible to extract parts of the facts set out in the figures and to combine them with other components and knowledge from the present specification. In particular, it should be noted that the figures and in particular the illustrated size ratios are merely schematic.

[0111] wherein:

[0112] Figure 1 An electric motor is shown in a perspective view, the electric motor being operated in a first state;

[0113] Figure 2 A part of an electric motor according to Figure 1 is shown in a perspective view, the electric motor being operated in a second state;

[0114] 3 shows a known electric motor arrangement in a first view;

[0115] Figure 4 shows an electric motor arrangement according to Figure 3 the second view;

[0116] Figure 5 shows the electric motor arrangement in a first switching state in a second state;

[0117] Figure 6 shows the electric motor arrangement according to Figure 5 the second view in a second switching state in a second state;

[0118] Figure 7 shows another embodiment variant of the electric motor arrangement. DETAILED DESCRIPTION

[0119] Figure 1 shows the electric motor 2 in a first state 10. The electric motor 2 comprises a stator 3 and a rotor 7. The electric motor 2 is an axial flux electric motor, wherein the stator 3 and the rotor 7 are arranged coaxially to each other and adjacently along an axial direction 38. The rotor 7 has first magnetic poles 8 and second magnetic poles 9 (not shown in detail) alternatingly along a circumferential direction 33. The stator 3 has six cores 36 extending along the axial direction 38 or a rotation axis 13. On each core 36 a coil 4, 5, 6 is arranged, respectively. Each coil 4, 5, 6 is electrically conductively connected to the electric circuit 1 (see Figures 3 to 7 ). The coils 4, 5, 6 are arranged in the following order along the circumferential direction 33: first coil 4, second coil 5, third coil 6, first coil 4, etc.

[0120] Each core 36 extends from a first end 39 of the stator 3 towards a second end 40 of the stator 3, wherein the rotor 7 is arranged adjacently to the second end 40.

[0121] A part of the housing of the electric motor 2 constitutes here a main body 35. The main body 35 extends completely along the circumferential direction 33 (outside the cores 36 or the coils 4, 5, 6 in the radial direction 34) and along the axial direction 38 (and the rotation axis 13 which stretches parallel thereto) from the second end 40 of the stator 3 up to the first end 39 of the stator 3. The main body 35 contacts the cores 36 of the coils 4, 5, 6 at the first end 39 of the stator 3. The main body 35 extends at the first end 39 along the radial direction 34 beyond the extension of the cores 36. The main body 35 constitutes here a pot with a cylindrical section (from the second end 40 up to the first end 39) and a bottom (at the first end 39).

[0122] In Figure 1The diagram shows at least two magnetic fluxes 37 used for the two coils 4 and 5, which occur when the motor 2 is energized according to the first state 10. The curves for each phase of the three-phase AC system 12 are shown in... Figure 1 The graph shows the current intensity 41 plotted on the vertical axis. The phase angle 42 plotted on the horizontal axis. It can be seen that the first frequency 29 of the three-phase AC system 12 is based on... Figure 2 The second frequency is more than 30 times the second frequency, which is drawn at a similar but different scale.

[0123] Figure 2 Shown in perspective according to Figure 1 Part of the electric motor 2, which operates in the second state 11. (Refer to...) Figure 1 The statement.

[0124] The rotor 7 is not shown here. Furthermore, the magnetic flux 37 occurring when the motor 2 is operated in the second state 11 is shown here.

[0125] In the second state 11, coils 4, 5, and 6 are loaded with in-phase alternating current. Therefore, there is no multiphase current, meaning that rotor 7 is not driven. An alternating magnetic field is generated by the alternating current. The change in magnetic flux 37 (dB / dt) generated by the magnetic field is related to the eddy current electric field (rotE). Due to the rapid change in magnetic flux 37, an eddy current density is obtained in the body 35, which ultimately accounts for or causes heat generation in the body 35.

[0126] The magnetic flux 37 is conducted through the body 35, so that the highest possible component of the electrical power of the motor 2 can be converted into heat through the body 35. The body 35 conducts the magnetic flux 37 from the second end 40 along the axial direction 38 to the first end 39 and then into the core 36.

[0127] exist Figure 2 In the graph, the curves for AC 14 are shown identically for all coils 4, 5, and 6. Current intensity 41 is plotted on the vertical axis. Phase angle 42 is plotted on the horizontal axis. It can be seen that the second frequency 30 of AC 14 is based on... Figure 1 The first frequency is more than 29 times that of the first frequency, which is plotted at a similar but different scale.

[0128] Figure 3 The first figure shows a known electric motor device 31. Figure 4 The second figure shows the following based on Figure 3 The electric motor assembly 31. It will be described below. Figure 3 and 4 Refer to the information about Figure 1 and 2 The statement.

[0129] The motor arrangement 31 comprises the motor 2, the circuit 1 and a control device 32 for operating the circuit 1 such that the motor 2 can be operated by the circuit 1 (see Figure 3 ), which comprises a stator 3 with three coils 4, 5, 6 and a rotor 7 (not shown).

[0130] The known circuit 1 for driving the motor 2 comprises a first potential line 15 and a second potential line 16, which are connected to different potentials of a DC voltage source 17, for example positive and ground, wherein between the potential lines 15, 16 three half-bridges 18, 19, 20 are arranged, wherein each coil 4, 5, 6 of the motor 2 is electrically conductively connected via a respective first line 21 to a respective half-bridge 18, 19, 20 and via a respective second line 22 to the other coils 4, 5, 6.

[0131] The three half-bridges 18, 19, 20 of the circuit 1 enable a three-phase alternating system 12 to be generated, in which the phases are offset by 120 degrees from one another. Each phase is passed on to the coils 4, 5, 6 via a respective first line 21. The coils 4, 5, 6 are connected to one another via the second lines 22, wherein the different phase currents cancel one another out in a star point 24, so that no return to a respective other potential line 16, 15 is required.

[0132] The half-bridges 18, 19, 20 comprise in particular in a known manner a device of an upper transistor 25 and a lower transistor 26, via which the potential lines 15, 16 are connected to one another. A diode 43 is connected in parallel to each transistor 25, 26. The first lines 21 are electrically conductively connected to the respective half-bridge 18, 19, 20 via a contact device 27.

[0133] In the illustration of Figure 4 , the transistors 25, 26 and diodes 43 are represented in a simplified manner as switches and are referred to as transistors 25, 26. Each coil is formed by a resistance R and an inductance L.

[0134] Figure 5 The motor arrangement 31 is shown in a first switching state in the second state 11. Figure 6 The motor arrangement 31 is shown in a second switching state in the second state 11. In the following Figure 5 and 6 are described together. Reference is made to the statements regarding Figure 3 and 4 and in particular to the simplified illustration of the half-bridges 18, 19, 20 according to Figure 4 .

[0135] According to Figure 3 and 4The motor arrangement 31 differs from the known circuit 1 in that the circuit 1 here has a fourth half-bridge 23 between the potential lines 15, 16, which can be in electrically conductive connection with the star point 24 to which the second line 22 is connected.

[0136] Supplementing the known circuit 1 by only one further half-bridge 23 and by its connection to the star point 24 leads to a known circuit 1 according to Figure 3 and 4 only a slight enlargement. Here, the fourth half-bridge 23 and its advantageous arrangement are however already able to achieve an additional realization of the second state 11.

[0137] Each half-bridge 18, 19, 20, 23 has at least one upper transistor 25 (high-side transistor) and a lower transistor 26 (low-side transistor), which are in electrically conductive connection with one another. The upper transistor 25 is in electrically conductive connection with the first potential line 15 and the lower transistor 26 is in electrically conductive connection with the second potential line 16. Each half-bridge 18, 19, 20, 23 has a contact device 27 between the upper transistor 25 and the lower transistor 26, via which one line 21, 22 can be connected to the respective half-bridge 18, 19, 20, 23.

[0138] Each first line 21 arranged on the motor 2 is thus in electrically conductive connection via the contact device 27 with one of the first, second and third half-bridges 18, 19, 20, respectively. The second line 22 or the star point 24 arranged at the motor 2 is connected via the contact device 27 to the fourth half-bridge 23.

[0139] In order to produce the second state 11, the circuit 1 can be operated such that, on the one hand (in the first circuit state, see Figure 5 ), the upper transistors 25 of the first half-bridge 18, the second half-bridge 19 and the third half-bridge 20 are in synchronism (i.e. in time parallel) to electrically conductively connect the first potential line 15 with the respective first line 21, while the lower transistors 26 of these half-bridges 18, 19, 20 electrically separate the respective first line 21 from the second potential line 16. The lower transistor 26 of the fourth half-bridge 23 is in synchronism therewith to electrically conductively connect the second line 22 with the second potential line 16. On the other hand (in the second circuit state, see Figure 6 ), the lower transistors 26 of the first half-bridge 18, the second half-bridge 19 and the third half-bridge 20 are in synchronism to electrically conductively connect the second potential line 16 with the respective first line 21, while the upper transistors 25 of these half-bridges 18, 19, 20 electrically separate the respective first line 21 from the first potential line 15. The upper transistor 25 of the fourth half-bridge 23 is in synchronism therewith to electrically conductively connect the second line 22 with the first potential line 15.

[0140] These circuit states are realized in time succession.

[0141] In these circuit states of the second state 11, the star point 24 is conductively connected via the fourth half bridge 23 to the potential lines 15, 16, respectively, so that a potential exists at each coil 4, 5, 6 in both circuit states. Since the upper and lower transistors 25, 26 of the first, second and third half bridges 18, 19, 20 are switched simultaneously and in the same manner, only a single-phase current exists. An alternating current 14 is generated by the transformation between the circuit states.

[0142] Figure 7 Another embodiment variant of the motor arrangement 31 is shown. Reference is made to the statements made with respect to Figure 5 and 6 .

[0143] Unlike Figure 5 and 6 , the circuit 1 comprises a capacitor 28, via which the star point 24 is connected to the fourth half bridge 23. In the operation of the motor 2, the capacitor 28 is arranged between the star point 24 and the fourth half bridge 23. The capacitor 28 is arranged in a series circuit between the motor 2 and the fourth half bridge 23.

[0144] The capacitance of the capacitor 28 is selected in dependence on the inductance of the coils 4, 5, 6 of the motor 2, so that, in the operation of the motor 2, the reactive power can be at least partially, preferably (almost) completely, compensated.

[0145] List of reference signs

[0146] 1 circuit

[0147] 2 motor

[0148] 3 stator

[0149] 4 first coil

[0150] 5 second coil

[0151] 6 third coil

[0152] 7 rotor

[0153] 8 first magnetic pole

[0154] 9 second magnetic pole

[0155] 10 first state

[0156] 11 second state

[0157] 12 three-phase alternating current system

[0158] 13 axis of rotation

[0159] 14 alternating current

[0160] 15 first potential connection

[0161] 16 second potential connection

[0162] 17 direct current voltage source

[0163] 18 first half bridge

[0164] 19 second half bridge

[0165] 20 third half bridge

[0166] 21 first connection

[0167] 22 second connection

[0168] 23 fourth half bridge

[0169] 24 star point

[0170] 25 upper transistor

[0171] 26 lower transistor

[0172] 27 contact means

[0173] 28 capacitor

[0174] 29 first frequency

[0175] 30 second frequency

[0176] 31 motor means

[0177] 32 control means

[0178] 33 circumferential

[0179] 34 radial direction

[0180] 35 main body

[0181] 36 core

[0182] 37 magnetic flux

[0183] 38 axial direction

[0184] 39 first end

[0185] 40 second end

[0186] 41 current intensity

[0187] 42 phase angle

[0188] 43 diode

Claims

1. A circuit (1) for an electric motor (2), wherein the electric motor (2) comprises at least one stator (3) having at least three coils (4, 5, 6) and a rotor (7) having at least two magnetic poles (8, 9); wherein the electric motor (2) is operable by the circuit (1) in at least two of the following states (10, 11): a) In the first state (10), the coils (4, 5, 6) can be loaded with different currents from the three-phase AC system (12), and the rotor (7) can be placed to rotate around the rotation axis (13); b) In the second state (11), the coils (4, 5, 6) can be loaded with in-phase alternating current (14); The circuit (1) has at least one first potential connection (15) and a second potential connection (16), which can be connected to different potentials of a DC voltage source (17). The circuit (1) includes three half-bridges (18, 19, 20) between the potential terminals (15, 16), wherein each coil (4, 5, 6) is electrically connected to one half-bridge (18, 19, 20) via a first terminal (21) and electrically connected to the other coils (4, 5, 6) via a second terminal (22); wherein the circuit (1) has a fourth half-bridge (23) between the potential terminals (15, 16), the fourth half-bridge being electrically connected to a star point (24) connected to the second terminal (22), wherein the circuit has at least one capacitor (28), the star point (24) being connected to the fourth half-bridge (23) via the capacitor.

2. The circuit (1) according to claim 1, wherein each half-bridge (18, 19, 20, 23) has at least one upper transistor (25) and a lower transistor (26), the upper transistor and the lower transistor being electrically connected to each other; wherein the upper transistor (25) is electrically connected to the first potential connection (15), and the lower transistor (26) is electrically connected to the second potential connection (16); wherein each half-bridge (18, 19, 20, 23) has a contact device (27) between the upper transistor (25) and the lower transistor (26), and a connection (21, 22) is connected to the corresponding half-bridge (18, 19, 20, 23) via the contact device.

3. The circuit (1) according to claim 2, in order to generate the second state (11), the circuit can be operated such that, on the one hand, the upper transistors (25) of the first half-bridge (18), the second half-bridge (19), and the third half-bridge (20) synchronously conduct the first potential connection (15) to the corresponding first connection (21), while the lower transistors (26) of these half-bridges (18, 19, 20) disconnect the corresponding first connection (21) from the second potential connection (26); wherein the lower transistor (26) of the fourth half-bridge (23) synchronously connects the second connection (21) to the corresponding first connection (22). 2) Conductively connected to the second potential connection (16); and on the other hand, the lower transistors (26) of the first half-bridge (18), the second half-bridge (19) and the third half-bridge (20) simultaneously conduct the second potential connection (16) to the corresponding first connection (21), while the upper transistors (25) of these half-bridges (18, 19, 20) disconnect the corresponding first connection (21) from the first potential connection (15); wherein the upper transistor (25) of the fourth half-bridge (23) simultaneously conducts the second connection (22) to the first potential connection (15).

4. The circuit (1) according to any one of claims 1 to 3, wherein the capacitance of the at least one capacitor (28) is selected according to the inductance of the coils (4, 5, 6) of the motor (2) such that reactive power can be at least partially compensated when the motor (2) is running.

5. A method for operating an electric motor (2) using a circuit (1) according to any one of claims 1 to 4; wherein the electric motor (2) is operated only through the first half-bridge (18), the second half-bridge (19) and the third half-bridge (20) to generate the first state (10).

6. The method according to claim 5, wherein during the first state (10), the star point (24) is electrically connected to only one potential connection (15, 16) or disconnected from both potential connections (15, 16) via the fourth half-bridge (23).

7. The method according to claim 5 or 6, wherein each half-bridge (18, 19, 20, 23) has at least one upper transistor (25) and a lower transistor (26), the upper transistor and the lower transistor being electrically connected to each other; wherein the upper transistor (25) is electrically connected to the first potential connection (15), and the lower transistor (26) is electrically connected to the second potential connection (16); wherein each half-bridge (18, 19, 20, 23) has a contact device (27) between the upper transistor (25) and the lower transistor (26), and a connection (21, 22) is connected to the respective half-bridge (18, 19, 20, 23) via the contact device; wherein, in order to generate the second state (11), On one hand, the upper transistors (25) of the first half-bridge (18), the second half-bridge (19), and the third half-bridge (20) are switched synchronously, and the first potential connection (15) is electrically connected to the corresponding first connection (21), while the lower transistors (26) of these half-bridges (18, 19, 20) disconnect the corresponding first connection (21) from the second potential connection (16); wherein the lower transistor (26) of the fourth half-bridge (23) is switched synchronously to connect the second connection (22) to the second potential connection (16); and On the other hand, the lower transistors (26) of the first half-bridge (18), the second half-bridge (19), and the third half-bridge (20) are switched synchronously to connect the second potential connection (16) to the corresponding first connection (21), while the upper transistors (25) of these half-bridges (18, 19, 20) disconnect the corresponding first connection (21) from the first potential connection (15); wherein the upper transistor (25) of the fourth half-bridge (23) is switched synchronously to connect the second connection (22) to the first potential connection (15).

8. The method according to claim 5 or 6, wherein the first frequency (29) of the three-phase current (12) has at most 50% of the second frequency (30) of the alternating current (14).

9. The method according to claim 5 or 6, wherein the maximum heating power that can be generated by the circuit (1) in the second state (11) is at least 50% of the driving power that can be generated by the circuit (1) in the first state (10).

10. The method according to claim 5 or 6, wherein the circuit (1) is operated at different time intervals to either generate the first state (10) or to generate the second state (11).

11. The method of claim 10, wherein the switching between the time intervals is performed at a third frequency exceeding 1 Hz.

12. An electric motor device (31) comprising at least an electric motor (2), the electric motor (2) comprising at least one stator (3) having at least three coils (4, 5, 6) and a rotor (7) having at least two magnetic poles (8, 9); a circuit (1) according to any one of claims 1 to 4; and a control device (32) for operating the circuit (1) such that the electric motor (2) can be operated using the method according to any one of claims 5 to 11.

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