ELECTRICAL CIRCUIT FOR AN ELECTRIC MOTOR

Description

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

[0002] There are known applications where, in addition to the drive power of an electric motor, the heating power of the electric motor can also be utilized. For example, when pumping a urea-water solution (e.g., AdBlue) used for exhaust gas treatment, heating the urea-water solution may be desired. The electric motor used to drive a pump also generates heat, which can be used, for example, to thaw the urea-water solution.

[0003] WO 2019 / 170738 A1 discloses a method for operating an electric motor that can be operated in at least two states. In a first state, the coils are operated with different electrical currents of a three-phase AC system, and the rotor is set in rotation about a rotational axis. In a second state, the coils are operated with an in-phase alternating current. The in-phase alternating current used in the second state enables, for example, targeted heating of components of a motor housing.

[0004] Typically, two different, separate or independently operable electrical circuits are used to generate these two states. This is considered necessary to meet the different requirements regarding the supplied electrical voltage and frequency.

[0005] For the first state, a low-frequency rotating field, for example, less than 1,000 Hz [Hertz], is generated between the potential terminals of the electrical circuit. For the second state, the generation of a high-frequency, for example, at least 5 kHz, in-phase alternating current between the potential terminals is required.

[0006] From DE 10 2018 104 418 A1 an electromagnetically actuated actuator for an electrical machine and an electrical machine with an electromagnetically actuated actuator are known.

[0007] WO 02 / 071809 A1 is directed to a device for the simultaneous heating by induction and stirring of a molten metal. Based on this, the object of the present invention is to at least alleviate or even solve the problems described with reference to the prior art. In particular, an electrical circuit is proposed with which an electric motor can be specifically operated to generate heating power.

[0008] To achieve these objects, an electrical circuit according to the features of patent claim 1 is proposed. Advantageous further developments are the subject of the dependent patent claims. The features listed individually in the patent claims can be combined with one another in a technologically expedient manner and can be supplemented by explanatory facts from the description and details from the figures, whereby further embodiments of the invention are shown.

[0009] An electrical circuit for an electric motor is proposed, wherein the electric motor has at least a first stator with at least three (or a multiple of three) coils and a rotor with at least two magnetic poles. The motor can be operated by the electrical circuit in at least the following two states: a) in a first state, the coils can be supplied with different (electrical) currents of a three-phase alternating current system (i.e. the individual currents are offset from one another by a phase angle) and the rotor can be set in rotation about an axis of rotation; b) in a second state, the coils can be supplied with an in-phase alternating current.

[0010] The electrical circuit has at least a first potential terminal and a second potential terminal, which are connectable or connected to different potentials (e.g., positive pole and ground) of a DC voltage source. The electrical circuit comprises three half-bridges between the potential terminals, wherein each coil is electrically conductively connectable or connected to a half-bridge via a first terminal and to the other coils via a second terminal. The electrical circuit has a fourth half-bridge between the potential terminals, which is electrically conductively connectable or connected to a star point connecting the second terminals.

[0011] The electric motor can also be operated as a generator. The explanations regarding the motor apply accordingly to operation as a generator.

[0012] The stator and rotor are arranged, in particular, side by side and coaxially with each other along an axial direction. The coils are arranged side by side along a circumferential direction (on a common diameter). This creates, in particular, an axial flux motor in which the magnetic flux between the coils and the magnetic poles runs parallel to the axis of rotation along an axial direction. However, other designs of the electric motor are also possible and can be used in combination with the electrical circuit.

[0013] In particular, the electric motor is a BLDC, i.e. a brushless direct current motor, in which the fixed stator contains the coils and the rotating rotor contains permanent magnets.

[0014] In particular, the power consumption of the electric motor in the second state (temporarily or at predeterminable intervals) occurs exclusively for heating a body. The body is arranged, in particular, at a distance from the stator and the rotor.

[0015] In addition, power consumption (temporarily or at predefined intervals) of the electrical circuit can occur additionally or exclusively to drive the rotor, so that the rotor rotates around a rotational axis at a speed of more than zero ("0") revolutions per minute.

[0016] In the second state, a body should or can be heated (primarily or essentially only), in particular by means of induction. The body can, for example, form a housing (or part thereof) of the electric motor. The body can form a conduit for a fluid, so that a fluid can be heated via the body. The body can, for example, be a shaft. A pump set, of which the shaft is a component, can be heated via a shaft. A fluid to be pumped by the pump set can therefore, for example, be heated via the shaft.

[0017] With induction heating, the heat is generated directly within the body itself, meaning it does not need to be transferred by conduction. The heating output is easily controllable. For inductive heating, a high-frequency (in-phase) alternating current is generated by the electrical circuit, which is then applied to the stator. This alternating magnetic field is generated in the stator coils, which generates eddy currents in the body material. Inductive heating can also occur through non-conductive materials (e.g., a wall, a housing, etc.). The surrounding area is heated only indirectly (primarily due to thermal radiation or conduction from the inductively heated body).

[0018] The stator of the electric motor, in particular, comprises a soft magnetic material, for example, a so-called "soft magnetic composite" (SMC), or a combination of electrical steel sheets and SMC. The stator coils comprise cores that are preferably made of a soft magnetic material that is pressed and bonded. The SMC material is not sintered. Instead, it is tempered below a melting temperature, which is nevertheless sufficient for the cores to permanently retain their geometry.

[0019] The rotor, in particular, has permanent magnets and / or soft magnetic elements or magnetic poles, for example, in recesses. Permanent magnets can preferably be used to form a permanently excited synchronous or brushless direct current motor, abbreviated to BLDC, while soft magnetic elements, for example, can be used to create a reluctance motor as an electric motor.

[0020] The structure of a stator, in particular using SMC, as well as further details regarding a rotor can be found, for example, in WO 2016 / 066714 A1.

[0021] The electric motor has in particular an electrical power consumption for the first state (i.e. a maximum drive power) of less than 1,000 watts (rated power), preferably less than 500 watts, particularly preferably less than 100 watts.

[0022] In particular, the electric motor consumes power to drive the rotor (first state), causing the rotor to rotate around a rotational axis at a speed greater than "0" revolutions per minute. The electric motor also consumes power to heat a body (second state).

[0023] In particular, the electric motor can be operated by the electric circuit in both states, so that the rotor is driven by the operation of the electric motor in the first state and, in parallel, a body is heated by the operation of the electric motor in the second state.

[0024] Temporally parallel here means in particular that within a time interval (e.g. one second) there is a change between the first state and the second state (in particular back and forth again and again), possibly for sub-intervals of different lengths of the time interval.

[0025] The heating power transferred to the body is in particular the electrical power [in watts] provided by the electrical circuit during operation in the second state.

[0026] Preferably, in the second state, (virtually) no electrical power is used to drive the rotor. In particular, despite the electric motor's power consumption, the rotor speed is "0" revolutions per minute.

[0027] In particular, the electric motor is not accelerated in the second state. This means, in particular, that the rotor speed may be greater than zero revolutions per minute, but that the rotor is not accelerated by the electrical power used exclusively for conversion into heat.

[0028] A conventional electrical circuit for driving an electric motor regularly comprises a first potential connection and a second potential connection, which can be connected to different potentials (e.g. positive pole and ground) of a DC voltage source, wherein three half-bridges are provided between the potential connections, wherein each coil of the electric motor can be electrically connected to a half-bridge via a first connection and to the other coils via a second connection.

[0029] The three half-bridges of the electrical circuit enable the generation of a three-phase alternating current system or multi-phase rectangular currents, with the phases offset by 120 degrees. Each current or phase current is transmitted to or impressed into a coil via a first connection. The coils are interconnected via second connections, with the different phase currents canceling each other out at the star point, thus eliminating the need for a separate or additional return conductor to the other potential connection.

[0030] A half-bridge comprises, in particular, in a known manner, an arrangement of an upper transistor and a lower transistor, via which the potential terminals are connected to each other. In particular, a diode is connected in parallel to each transistor.

[0031] Adding just one more half-bridge to the known electrical circuit and connecting it to the star point results in only a slight increase in the size of the known electrical circuit. However, this fourth half-bridge and its advantageous arrangement already enable the additional realization of the second state.

[0032] According to the invention, each half-bridge has at least one upper transistor (high-side transistor) and one lower transistor (low-side transistor), which are electrically connected to one another. The upper transistor is electrically connected to the first potential terminal, and the lower transistor is electrically connected to the second potential terminal. Each half-bridge has a contact between the upper transistor and the lower transistor, via which the respective terminal can be connected to the respective half-bridge.

[0033] Each first terminal, located on the electric motor, for example, is electrically connected to one of the first, second, or third half-bridges via the contact. The second terminals or the star point, located on the electric motor, for example, are connected to the fourth half-bridge via the contact.

[0034] According to the invention, the electrical circuit for generating the second state is operable such that, on the one hand (in a first circuit state), the upper transistors of the first half-bridge, the second half-bridge, and the third half-bridge synchronously (i.e., temporally parallel) electrically connect the first potential terminal to the respective first terminal, while the lower transistors of these half-bridges (electrically) disconnect the respective first terminals from the second potential terminal. Synchronously, the lower transistor of the fourth half-bridge electrically connects the second terminal to the second potential terminal.On the other hand (in a second circuit state), the lower transistors of the first half-bridge, the second half-bridge, and the third half-bridge synchronously electrically connect the second potential terminal to the respective first terminal, while the upper transistors of these half-bridges (electrically) disconnect the respective first terminals from the first potential terminal. Synchronously, the upper transistor of the fourth half-bridge electrically connects the second terminal to the first potential terminal. Therefore, if an in-phase current is to be present in heating mode (second state), all first terminals are at the same potential. In this case, a potential difference can only be generated by adding an additional return conductor, in this case via the fourth half-bridge.

[0035] These circuit states are realized in particular one after the other.

[0036] In these second-state circuit states, the star point is electrically connected to a potential terminal via the fourth half-bridge, so that an electrical potential difference exists across each coil in both circuit states. Since the upper or lower transistors of the first, second, and third half-bridges switch simultaneously and in the same manner, only a single-phase current is present. An alternating current is generated by switching between the circuit states.

[0037] According to the invention, the electrical circuit comprises at least one capacitor, via which the star point can be connected to the fourth half-bridge. The capacitor is arranged between the star point and the fourth half-bridge during operation of the electric motor.

[0038] The at least one capacitor is arranged in particular in a series circuit between the electric motor and the fourth half-bridge.

[0039] Alternatively, the at least one capacitor is arranged in a parallel circuit between the first terminal and the second terminal. In particular, one or more compensation capacitors are connected in parallel for each phase, in particular between the first and second terminals of the coil(s) connected together to form a phase. It should be noted that if the PWM signal used to generate the current waveform in the first state has a similar frequency to the heating frequency, a current smoothing effect of the motor inductance is disabled, thus making targeted current waveform generation impossible. To avoid this problem, the PWM frequency and the heating frequency should be far apart.

[0040] In particular, a capacitance of the at least one capacitor is selected depending on an inductance of the coils of the motor, so that reactive power can be at least partially compensated when the motor is operated.

[0041] Without at least one capacitor, the heating power that can be generated, for example in low-voltage systems, such as automotive applications, would be particularly limited, since the coil current is limited due to the high impedance of the coils at high frequencies of the alternating current. The impedance of a coil increases proportionally with the frequency according to Z = j 2 π f L, where Z: Impedance of a coil j: Imaginary unit f: Frequency of the alternating current L: Inductance of the coil

[0042] Since the terminal potentials of the electrical circuit are connected to a DC voltage source (or to a sink in generator mode), this would require a correspondingly high voltage. However, this is not feasible, especially in automotive applications with low on-board voltages. In particular, reactive power compensation can be achieved by achieving a resonance state through the arrangement of at least one capacitor. In this case, the required voltage between the potential terminals can also be generated with a significantly lower DC voltage.

[0043] The phase voltage drop across a coil of the electric motor can generally be determined by multiplying the coil impedance by the phase current: U _ = Z _ ⋅ I _

[0044] The coil impedance can always be described by a frequency-independent real part and a frequency-dependent imaginary part. Taking into account parasitic components and other frequency-dependent effects or loss mechanisms, a complex relationship between current and voltage results. However, the impedance can be represented to a good approximation as a simplified relationship for both states. In the first state, the ohmic wire resistance of a coil phase forms the real part of the impedance, while the inductive behavior can be expressed by the imaginary part of the impedance. The phase voltage (voltage between the first terminal and the second terminal, i.e., the voltage drop across a coil) can be calculated for this first state using the following formula: U _ = I _ ⋅ R i + j 2 πfL i , where U:Phase voltage, i.e. voltage between the respective potential connection electrically connected via the first connections and the second connection 1:electrical current supplied to the electric motor; R i :resistance of the respective coil or the current path running through the coil j:imaginary unit f:frequency of the alternating current L i :inductance of the respective coil

[0045] For the second state, however, this description of the coil impedance is particularly insufficient. The iron losses occurring in the body should be considered more precisely. The coil or magnetic circuit is lossy, so an additional component can be defined in the real part, to which the active power losses occurring in the body can be attributed. Due to the in-phase nature, the motor phases in this state can be considered a parallel circuit, so that the phase voltage for the second state can be expressed to a good approximation by the following equation: U _ = I _ ⋅ R i 3 + R v + j 2 πf L i 3 , where R v :Resistance to describe the loss component in the second state

[0046] The arrangement of at least one capacitor changes the above equation as follows: U _ = I _ ⋅ R i 3 + R v + j 2 πf L i 3 − 1 2 πfC , where C:Capacitance of at least one capacitor

[0047] The capacitance of at least one capacitor should be chosen so that: 2 πf L i 3 = 1 2 πfC

[0048] This allows the imaginary and frequency-dependent component to be completely compensated and the voltage requirement to be drastically reduced, so that: U _ = I _ ⋅ R i 3 + R v

[0049] Due to the high phase voltage of the electric motor, i.e. the voltage between the first terminals and the second terminals, a sufficiently high dielectric strength and the lowest possible ESR (equivalent series resistance) should be taken into account when dimensioning at least one capacitor in order to reduce compensation losses. Furthermore, frequency stability as a function of temperature must be guaranteed, since, for example, capacitors experience a change in their capacitance depending on temperature, but coil cores can also behave depending on temperature. If the resonance state is detuned, i.e. the capacitance changes, for example, with temperature, a different frequency is required to maximize the power loss. In this case, the frequency can be readjusted using a control unit, e.g. a microprocessor. A measurement of the current, e.g.Shunt resistors (usually low-side shunts) can be used to maximize current and thus minimize losses. In particular, a current can be measured and a frequency adjusted alternately, and these steps can be repeated multiple times.

[0050] A method for operating an electric motor with the described electrical circuit is further proposed. To generate the first state, the motor is operated exclusively via the first half-bridge, the second half-bridge, and the third half-bridge.

[0051] In particular, during the first state, the star point is electrically connected via the fourth half-bridge only to one potential terminal or is (electrically) separated from both potential terminals (i.e. arranged in a floating manner).

[0052] In particular, each half-bridge has at least one upper transistor and one lower transistor that are electrically connected to one another; the upper transistor is electrically connected to the first potential terminal and the lower transistor is electrically connected to the second potential terminal. Each half-bridge has a contact between the upper transistor and the lower transistor, via which one terminal is connected to the respective half-bridge. To generate the second state: on the one hand, the upper transistors of the first half-bridge, the second half-bridge and the third half-bridge are connected synchronously and the first potential terminal is electrically connected to the respective first terminal, while the lower transistors of these half-bridges are connected synchronously and separate the respective first terminals from the second potential terminal; wherein synchronously therewith, the lower transistor of the fourth half-bridge is connected to connect the second terminal to the second potential terminal; and on the other hand, the lower transistors of the first half-bridge, the second half-bridge and the third half-bridge are connected synchronously and the second potential terminal is electrically connected to the respective first terminal, while the upper transistors of these half-bridges are connected synchronously and separate the respective first terminals from the first potential terminal;wherein synchronously therewith the upper transistor of the fourth half-bridge is switched to connect the second terminal to the first potential terminal. ;

[0053] The three-phase alternating current system of the first state is generated in a known manner by the controlled switching of the first, second and third half-bridge.

[0054] In particular, a first frequency of the three-phase system has at most 50%, preferably at most 10%, particularly preferably at most 2%, of a second frequency of the alternating current.

[0055] The first frequency of the three-phase system (i.e. the number of periods of a phase of the three-phase system per second) is in particular not more than 1,000 Hz, in particular not more than 500 Hz.

[0056] The second frequency of the alternating current (where two potential changes occur per period) is in particular at least 5 kHz, preferably at least 10 kHz, particularly preferably at least 15 kHz.

[0057] In particular, a maximum heating power that can be generated by the electrical circuit in the second state is at least 50%, preferably at least 100%, particularly preferably at least 200%, of a drive power that can be generated by the electrical circuit in the first state.

[0058] In particular, a maximum heating power that can be generated by the electrical circuit in the second state is higher by a factor of at least five, preferably at least 10, particularly preferably at least 25 or even at least 45, than a drive power that can be generated by the electrical circuit in the first state.

[0059] If the electrical power consumption for the first state (i.e. maximum drive power) is up to 1,000 watts (rated power), the power consumption for the second state can be at least 5 kW [kilowatts], 10 kW, 25 kW or even 45 kW.

[0060] In particular, the electrical circuit is operated at different time intervals either to generate the first state or to generate the second state.

[0061] In particular, switching between the time intervals takes place at a third frequency of more than one ("1") Hz, in particular of more than 5 Hz, preferably of more than 20 Hz and particularly preferably of more than 100 Hz.

[0062] In particular, the time intervals assigned to the respective state can be of different lengths. In particular, first time intervals in which the motor is operated in the first state are longer, e.g., by at least 10%, at least 20%, or at least 40%, than second time intervals in which the motor is operated in the second state.

[0063] In particular, the time portions in which a motor is operated in the first state or in the second state can be designed differently.

[0064] In particular, first time intervals and / or second time intervals can be of different lengths.

[0065] In particular, different electrical powers can be provided in different first and / or second time intervals.

[0066] In particular, different electrical parameters may be present in different first and / or second time intervals, e.g., frequency, current, etc.

[0067] Furthermore, a motor arrangement is proposed, at least comprising an electric motor having at least one stator with at least three coils and a rotor with at least two magnetic poles, the described electrical circuit and a control device for controlling the electrical circuit, so that the motor can be operated using the described method.

[0068] The control device is in particular equipped, configured or programmed so that the electrical circuit can be operated according to the described method.

[0069] Preferably, an electrically conductive body is arranged in a radial direction at least inside or outside at least the stator, which is heated by induction at least during operation of the electric motor in the second state.

[0070] Alternatively or additionally, the body can be the rotor. In addition to the magnetic poles, the rotor has a carrier material called the body.

[0071] In particular, a specific electrical first resistance [Ohm * Millimeter 2< / Meter] of the body is lower than a specific electrical second resistance of a core of a coil.

[0072] In particular, the SMC material used for the core has a high electrical resistivity. In particular, the body (e.g., made of steel) has a lower electrical resistivity (than the material used for the core).

[0073] In particular, the body serves to convert the electrical power provided in the second state into heat. Preferably, the body has high electrical and / or magnetic conductivity or is made of iron, so that effective heating is possible. In particular, the core of a coil has significantly lower electrical conductivity than the body, so that eddy currents in the core are suppressed. With regard to magnetic conductivity, the body and core can, in particular, be identical or similar.

[0074] In particular, a specific electrical first resistance is lower than a specific electrical second resistance by a factor of at least two, preferably at least five, particularly preferably at least 10.

[0075] In particular, each coil of the stator has a core which extends from a first end to a second end of the at least one stator (in particular parallel to the axial direction), wherein the rotor is arranged adjacent to the at least one second end.

[0076] The body extends in particular along a circumferential direction completely (in a radial direction inside or outside the cores or the coils) and along an axial direction (and the axis of rotation running parallel thereto) up to the at least one first end of the core.

[0077] Preferably, the body contacts the cores of the coils at at least one first end.

[0078] In particular, the magnetic flux is directed through the body in such a way that as high a proportion as possible of the electrical power of the electric motor can be converted into heat by the body.

[0079] In particular, the body extends from an end face of the rotor facing away from the first stator along the axial direction and in a radial direction inside or outside the coils up to the first end.

[0080] In particular, the body extends at the at least one first end along the radial direction at least over the extent of the cores.

[0081] 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 to at least over the extent of the cores (in alignment with the rotor).

[0082] In particular, a pump for conveying a fluid can be driven via the electric motor, wherein in the first state the pump (for conveying the fluid) is operated and in the second state at least the fluid conveyable by the pump is heated.

[0083] In the second state, the coils are driven by a single-phase alternating current. In particular, there is no multiphase current present, so the rotor is not driven. The alternating current generates an alternating magnetic field, which can generate heat in the body through induction.

[0084] The explanations regarding the electrical circuit apply equally to the process and the motor arrangement and vice versa.

[0085] An electrical circuit is proposed that uses electrical power for an electric motor to drive a rotor (i.e., to perform a rotary motion) and to specifically heat a body using induction. The body can also be heated exclusively, without driving the rotor at all. This is particularly advantageous for fluids that can freeze, such as urea-water solutions, which have a freezing point of approximately -11 degrees Celsius. Thus, a fluid stored in a tank can be thawed through the body and then pumped in increasing quantities.

[0086] The use of indefinite articles ("a", "an", "an" and "another"), particularly in the patent claims and the description reproducing them, is to be understood as such and not as a numeral. Terms or components introduced accordingly are therefore to be understood as appearing at least once and, in particular, as being able to appear multiple times.

[0087] As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily specify any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment. To the extent that a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or part of the majority of these components, but this is not mandatory.

[0088] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and, in particular, the illustrated proportions are only schematic. They show: Fig. 1: an electric motor in perspective view, operated in a first state; Fig. 2: a part of the electric motor according to Fig. 1 in perspective view, operated in a second state; Fig. 3: a known motor arrangement in a first representation; Fig. 4: the motor arrangement according to Fig. 3in a second representation; Fig. 5: a motor arrangement in a first switching state of the second state; Fig. 6: the motor arrangement according to Fig. 5 in a second switching state of the second state; Fig. 7: a further embodiment of a motor arrangement.

[0089] Fig. 1shows an electric motor 2 in perspective view, operated 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 motor, wherein the stator 3 and rotor 7 are arranged coaxially to one another and next to one another along an axial direction 38. The rotor 7 has alternating first magnetic poles 8 and second magnetic poles 9 (not shown in detail) along the circumferential direction 33. The stator 3 has six cores 36, which extend along the axial direction 38 or the axis of rotation 13. A coil 4, 5, 6 is arranged on each core 36. Each coil 4, 5, 6 is connected to an electrical circuit 1 (see Fig. 3 to 7 ) are electrically connected. The coils 4, 5, 6 are arranged along the circumferential direction 33 in the following order: first coil 4, second coil 5, third coil 6, first coil 4, etc.

[0090] Each core 36 extends from a first end 39 of the stator 3 to a second end 40 of the stator 3, with the rotor 7 being arranged adjacent to the second end 40.

[0091] A part of the housing of the electric motor 2 forms a body 35. The body 35 extends along a circumferential direction 33 completely (in a radial direction 34 outside the cores 36 or the coils 4, 5, 6) and along an axial direction 38 (and the axis of rotation 13 running parallel thereto) starting from the second end 40 of the stator 3 up to the first end 39 of the stator 3. The body 35 contacts the cores 36 of the coils 4, 5, 6 at the first end 39 of the stator 3. The body 35 extends at the first end 39 along the radial direction 34 up to the extent of the cores 36. The body 35 forms a pot with a cylindrical section (starting from the second end 40 up to the first end 39) and a bottom (at the first end 39).

[0092] In Fig. 1the magnetic flux 37 is shown at least for two coils 4, 5, which is established when the electric motor 2 is energized according to the first state 10. In the diagram of the Fig. 1 The curves of the individual phases of the three-phase alternating current system 12 are shown. The current intensity 41 is plotted on the vertical axis. The phase angle 42 is plotted on the horizontal axis. It can be seen that the first frequency 29 of the three-phase alternating current system 12 is several times lower than the second frequency 30 plotted on a similar but different scale according to Fig. 2 .

[0093] Fig. 2 shows a part of the electric motor 2 after Fig. 1 in perspective view, operated in a second state 11. The comments on Fig. 1 is referred to.

[0094] Here, the rotor 7 is not shown. Also shown is the magnetic flux 37, which is established during operation of the electric motor 2 according to the second state 11.

[0095] In the second state 11, the coils 4, 5, and 6 are supplied with an in-phase alternating current. There is then no multiphase current, so that the rotor 7 is not driven. An alternating magnetic field is generated via the alternating current. The change in the magnetic flux 37 (dB / dt) generated by the magnetic field is linked to an electric vortex field (rotE). As a result of the rapid change in the magnetic flux 37, an eddy current density arises in the body 35, which ultimately is responsible for, or causes, the heat generation in the body 35.

[0096] The magnetic flux 37 is conducted through the body 35 in such a way that the highest possible proportion of the electrical power of the electric motor 2 can be converted into heat by 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 back into the cores 36.

[0097] In the diagram of the Fig. 2 The curve of the alternating current 14 is shown, the same for all coils 4, 5, 6. The current intensity 41 is plotted on the vertical axis. The phase angle 42 is plotted on the horizontal axis. It can be seen that the second frequency 30 of the alternating current 14 is several times higher than the first frequency 29 plotted on a similar but different scale according to Fig. 1 .

[0098] Fig. 3 shows a known motor arrangement 31 in a first representation. Fig. 4 shows the engine arrangement 31 according to Fig. 3in a second representation. The Figs. 3 and 4 are described together below. The explanations for Fig. 1 and 2 is referred to.

[0099] The motor arrangement 31 comprises an electric motor 2, which has a stator 3 with three coils 4, 5, 6 and a rotor 7 (not shown), an electrical circuit 1 and a control device 32 (see Fig. 3 ) for controlling the electrical circuit 1, so that the motor 2 can be operated via the electrical circuit 1.

[0100] The known electrical circuit 1 for driving an electric motor 2 comprises a first potential connection 15 and a second potential connection 16, which are connected to different potentials (e.g. positive pole and ground) of a DC voltage source 17, wherein three half-bridges 18, 19, 20 are provided between the potential connections 15, 16, wherein each coil 4, 5, 6 of the electric motor 2 is electrically conductively connected via a first connection 21 to a half-bridge 18, 19, 20 and via a second connection 22 to the other coils 4, 5, 6.

[0101] The three half-bridges 18, 19, 20 of the electrical circuit 1 enable the generation of a three-phase alternating current system 12, with the phases offset from one another by 120 degrees. Each phase is transmitted to a coil 4, 5, 6 via a first terminal 21. The coils 4, 5, 6 are interconnected via second terminals 22, with the different phase currents canceling each other out at the star point 24, so that no return conductor to the respective other potential terminal 16, 15 is required.

[0102] A half-bridge 18, 19, 20 comprises, in particular, in a known manner, an arrangement of an upper transistor 25 and a lower transistor 26, via which the potential terminals 15, 16 are connected to one another. A diode 43 is connected in parallel to each transistor 25, 26. The first terminals 21 are electrically connected to the respective half-bridge 18, 19, 20 via contacts 27.

[0103] In the presentation of the Fig.4 The transistors 25, 26 and diodes 43 are simplified as switches and referred to as transistors 25, 26. Each coil is formed by an electrical resistance R and an electrical inductance L.

[0104] Fig. 5 shows a motor arrangement 31 in a first switching state of the second state 11. Fig. 6 shows a motor arrangement 31 in a second switching state of the second state 11. The Fig. 5 and 6 are described together below. The explanations regarding the Figs. 3 and 4 and in particular the explanations regarding the simplified representation of the half-bridges 18, 19, 20 according to Fig. 4 reference is made.

[0105] In contrast to the engine arrangements 31 according to Figs. 3 and 4the electrical circuit 1 here has a fourth half-bridge 23 between the potential terminals 15, 16, which can be electrically connected to a star point 24 connecting the second terminals 22.

[0106] The addition of only one further half-bridge 23 to the known electrical circuit 1 and its connection to the star point 24 results in only a slight enlargement of the known electrical circuit 1 according to Figs. 3 and 4 . However, this fourth half-bridge 23 and its advantageous arrangement already enables the additional realization of the second state 11.

[0107] Each half-bridge 18, 19, 20, 23 has at least one upper transistor 25 (high-side transistor) and one lower transistor 26 (low-side transistor), which are electrically connected to one another. The upper transistor 25 is electrically connected to the first potential terminal 15, and the lower transistor 26 is electrically connected to the second potential terminal 16. Each half-bridge 18, 19, 20, 23 has a contact 27 between the upper transistor 25 and the lower transistor 26, via which the respective terminal 21, 22 can be connected to the respective half-bridge 18, 19, 20, 23.

[0108] Each first terminal 21 arranged on the electric motor 2 is thus electrically connected to one of the first, second, and third half-bridges 18, 19, 20 via the contact 27. The second terminals 22 or the star point 24 arranged on the electric motor 2 are connected to the fourth half-bridge 23 via the contact 27.

[0109] The electrical circuit 1 is operable to generate the second state 11 in such a way that, on the one hand (in a first circuit state, see Fig. 5 ) the upper transistors 25 of the first half-bridge 18, the second half-bridge 19 and the third half-bridge 20 synchronously (i.e., in parallel in time) electrically connect the first potential terminal 15 to the respective first terminal 21, while the lower transistors 26 of these half-bridges 18, 19, 20 (electrically) separate the respective first terminals 21 from the second potential terminal 16. Synchronously, the lower transistor 26 of the fourth half-bridge 23 electrically connects the second terminal 22 to the second potential terminal 16. On the other hand (in a second circuit state, see Fig. 6), the lower transistors 26 of the first half-bridge 18, the second half-bridge 19, and the third half-bridge 20 synchronously electrically connect the second potential terminal 16 to the respective first terminal 21, while the upper transistors 25 of these half-bridges 18, 19, 20 (electrically) separate the respective first terminals 21 from the first potential terminal 15. Synchronously, the upper transistor 25 of the fourth half-bridge 23 electrically connects the second terminal 22 to the first potential terminal 15.

[0110] These circuit states are realized one after the other.

[0111] In these circuit states of the second state 11, the star point 24 is electrically connected to a potential terminal 15, 16 via the fourth half-bridge 23, so that an electrical potential is present at each coil 4, 5, 6 in both circuit states. Since the upper or lower transistors 25, 26 of the first, second, and third half-bridges 18, 19, 20 switch simultaneously and in the same manner, only a single-phase current is present. An alternating current 14 is generated by the change between the circuit states.

[0112] Fig. 7 shows a further embodiment of a motor arrangement 31. The explanations for Fig. 5 and 6 reference is made.

[0113] In contrast to Fig. 5 and 6The electrical circuit 1 comprises a capacitor 28, via which the star point 24 is connected to the fourth half-bridge 23. During operation of the electric 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 electric motor 2 and the fourth half-bridge 23.

[0114] A capacitance of the capacitor 28 is selected depending on an inductance of the coils 4, 5, 6 of the motor 2, so that when the motor 2 is operated, a reactive power can be compensated at least partially, preferably (almost) completely. List of reference symbols

[0115] 1 Electrical circuit 2 Motor 3 Stator 4 First coil 5 Second coil 6 Third coil 7 Rotor 8 First magnetic pole 9 Second magnetic pole 10 First state 11 Second state 12 Three-phase AC system 13 Axis of rotation 14 Alternating current 15 First potential connection 16 Second potential connection 17 DC voltage source 18 First half-bridge 19 Second half-bridge 20 Third half-bridge 21 First connection 22 Second connection 23 Fourth half-bridge 24 Star point 25 Upper transistor 26 Lower transistor 27 Contact 28 Capacitor 29 First frequency 30 Second frequency 31 Motor arrangement 32 Control device 33 Circumferential direction 34 Radial direction 35 Body 36 Core 37 Magnetic flux 38 Axial direction 39 First end 40 Second end 41Current 42Phase angle 43Diode

Claims

1. Electric circuit (1) for an electric motor (2), wherein the electric motor (2) has at least one stator (3) with at least three coils (4, 5, 6) and one rotor (7) with at least two magnetic poles (8, 9); wherein the motor (2) can be operated by the electric circuit (1) at least in the following two states (10, 11): a) in a first state (10), respectively different currents of a three-phase system (12) can be applied to the coils (4, 5, 6) and the rotor (7) can be caused to rotate about an axis of rotation (13); b) in a second state (11), an in-phase alternating current (14) can be applied to the coils (4, 5, 6); wherein the electric circuit (1) has at least one first potential connection (15) and one second potential connection (16) which can be connected to different potentials of a DC voltage source (17), wherein the electric circuit (1) comprises three half-bridges (18, 19, 20) between the potential connections (15, 16), wherein each coil (4, 5, 6) can be connected in an electrically conductive manner to one half-bridge (18, 19, 20) in each case via one first connection (21) in each case and can be connected in an electrically conductive manner to the other coils (4, 5, 6) via one second connection (22) in each case; wherein the electric circuit (1) has a fourth half-bridge (23) between the potential connections (15, 16), which fourth half-bridge can be connected in an electrically conductive manner to a star point (24) connecting the second connections (22); wherein each half-bridge (18, 19, 20, 23) has at least one upper transistor (25) and one lower transistor (26) which are connected to one another in an electrically conductive manner; wherein the upper transistor (25) is connected in an electrically conductive manner to the first potential connection (15) and the lower transistor (26) is connected in an electrically conductive manner to the second potential connection (16); wherein each half-bridge (18, 19, 20, 23) has a contact-connection (27) between the upper transistor (25) and the lower transistor (26), which contact-connection can be used to connect the respective one connection (21, 22) to the respective half-bridge (18, 19, 20, 23); characterized in that the electrical circuit (1), in order to produce the second state (11), can be operated in such a manner that, on the one hand, the upper transistors (25) of the first half-bridge (18), of the second half-bridge (19) and of the third half-bridge (20) synchronously connect the first potential connection (15) to the respective first connection (21) in an electrically conductive manner, while the lower transistors (26) of these half-bridges (18, 19, 20) disconnect the respective first connections (21) from the second potential connection (16); wherein, in sync with this, the lower transistor (26) of the fourth half-bridge (23) connects the second connection (22) to the second potential connection (16) in an electrically conductive manner; and that, on the other hand, the lower transistors (26) of the first half-bridge (18), of the second half-bridge (19) and of the third half-bridge (20) synchronously connect the second potential connection (16) to the respective first connection (21) in an electrically conductive manner, while the upper transistors (25) of these half-bridges (18, 19, 20) disconnect the respective first connections (21) from the first potential connection (15); wherein, in sync with this, the upper transistor (25) of the fourth half-bridge (23) connects the second connection (22) to the first potential connection (15) in an electrically conductive manner; wherein the electrical circuit (1) has at least one capacitor (28) which can be used to connect the star point (24) to the fourth half-bridge (23).

2. Electric circuit (1) according to claim 1, wherein a capacitance of the at least one capacitor (28) is selected on the basis of an inductance of the coils (4, 5, 6) of the motor (2), such that a reactive power can be at least partially compensated for during operation of the motor (2).

3. Method for operating an electric motor (2) using an electric circuit (1) according to one of the preceding claims; wherein, in order to produce the first state (10), the motor (2) is operated solely via the first half-bridge (18), the second half-bridge (19) and the third half-bridge (20).

4. Method according to claim 3, wherein the star point (24) is connected only to one potential connection (15, 16) in an electrically conductive manner via the fourth half-bridge (23) or is disconnected from both potential connections (15, 16) during the first state (10).

5. Method according to either of the preceding claims 3 and 4, wherein each half-bridge (18, 19, 20, 23) has at least one upper transistor (25) and one lower transistor (26) which are connected to one another in an electrically conductive manner; wherein the upper transistor (25) is connected to the first potential connection (15) in an electrically conductive manner and the lower transistor (26) is connected to the second potential connection (16) in an electrically conductive manner; wherein each half-bridge (18, 19, 20, 23) has a contact-connection (27) between the upper transistor (25) and the lower transistor (26), which contact-connection is used to connect the respective one connection (21, 22) to the respective half-bridge (18, 19, 20, 23); wherein, in order to produce the second state (11), • on the one hand, the upper transistors (25) of the first half-bridge (18), of the second half-bridge (19) and of the third half-bridge (20) are synchronously switched and connect the first potential connection (15) to the respective first connection (21) in an electrically conductive manner, while the lower transistors (26) of these half-bridges (18, 19, 20) disconnect the respective first connections (21) from the second potential connection (16); wherein, in sync with this, the lower transistor (26) of the fourth half-bridge (23) is switched for the purpose of connecting 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), of the second half-bridge (19) and of the third half-bridge (20) are synchronously switched and connect the second potential connection (16) to the respective first connection (21) in an electrically conductive manner, while the upper transistors (25) of these half-bridges (18, 19, 20) disconnect the respective first connections (21) from the first potential connection (15); wherein, in sync with this, the upper transistor (25) of the fourth half-bridge (23) is switched for the purpose of connecting the second connection (22) to the first potential connection (16).

6. Method according to one of the preceding claims 3 to 5, wherein a first frequency (29) of the three-phase current (20) is at most 50% of a second frequency (30) of the alternating current (14).

7. Method according to one of the preceding claims 3 to 6, wherein a maximum heating power that can be produced by the electric circuit (1) in the second state (11) is at least 50% of a drive power that can be produced by the electric circuit (1) in the first state (10).

8. Method according to one of the preceding claims 3 to 7, wherein the electric circuit (1) is operated either to produce the first state (10) or to produce the second state (11) in intervals of time which differ from one another.

9. Method according to claim 8, wherein there is a changeover between the intervals of time at a third frequency of more than one Hz.

10. Motor arrangement (31) at least comprising an electric motor (2) which has at least one stator (3) with at least three coils (4, 5, 6) and one rotor (7) with at least two magnetic poles (8, 9), an electric circuit (1) according to one of the preceding claims 1 and 2 and a control device (32) for controlling the electric circuit (1) such that the motor (2) can be operated with a method according to one of the preceding claims 3 to 9.