Drive systems with harmonic infeed

Abstract

The present invention relates to a drive system. The drive system includes an electric motor configured as a synchronous motor. The electric motor includes a rotor and at least one stator, the rotor being configured to rotate about an axis of rotation and having at least one separately excited rotor winding, and the stator having at least two stator winding sets, each stator winding set having at least three stator windings. The drive system also includes a control unit configured and constructed such that, during operation, a first current signal is applied to the at least one rotor winding and, during operation, different current phases of a multi-phase second current signal are at least partially applied to the stator winding, thereby forming a rotating magnetic field for generating a torque acting on the rotor. Furthermore, the drive system includes at least one inverter and at least one rectifier, wherein the multi-phase current signal applied to the stator winding is provided based on the at least one inverter, and a DC signal is provided by the rectifier. The first current signal applied to the at least one rotor winding is based at least on the DC signal provided by the rectifier and a harmonic AC component. Harmonics of at least one current phase of a multiphase current signal are reduced by applying the at least one harmonic AC component to the at least one rotor winding, which harmonics are caused by magnetic coupling occurring during operation between the at least one rotor winding and a stator winding.

Description

Technical Field

[0001] The invention relates to a drive system and an electrically drivable vehicle. Background Art

[0002] Drive systems including electric motors, particularly electric motors, are used in a wide variety of applications today. Electric motors are also used as electric drive machines in electrically driven vehicles. In this context, electric drive machines are specifically understood to be electric motors that generate propulsion in the form of torque for a motor vehicle. In this context, the electrical energy from batteries or accumulators must be used as efficiently as possible. Ideally, the efficiency and torque of the electric motors should be optimized for this purpose. Synchronous motors are often used for this purpose.

[0003] A synchronous motor consists of at least one rotor and a stator, with an air gap formed between them. The rotor of a synchronous motor has permanent magnets or a separately excited rotor winding. The stator includes stator windings. When current is applied to these windings, a rotating magnetic field forms in the air gap, generating a torque that drives the rotor.

[0004] Synchronous motors with an increased number of stator windings allow for higher maximum achievable motor power. However, during operation, magnetic coupling occurs between the stator and rotor windings. This can induce harmonics through rotor resonance in the stator winding phase currents. These harmonics cause losses, negatively impacting the maximum achievable machine power. Furthermore, the involved components are subject to increased loads, which can negatively impact their service life.

[0005] Harmonics can often be mitigated or avoided with additional filters. However, such filters increase the complexity, weight, and cost of the drive system. Other approaches include providing wide-bandwidth current regulation. However, this requires increasing the switching frequency of the participating inverters, which in turn leads to increased losses. Summary of the Invention

[0006] The underlying technical object can be seen as providing a drive system and an electrically drivable vehicle, by means of which, on the one hand, an increased power output is provided, but at the same time losses are reduced.

[0007] This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments, developments and variants are the subject matter of the dependent claims.

[0008] The present invention particularly provides a drive system. The drive system includes a motor. The motor is configured as a synchronous motor.

[0009] The electric machine includes a rotor configured to be rotatable about a rotation axis and having at least one separately excited rotor winding.

[0010] The electric machine further comprises at least one stator having at least two stator winding sets, each stator winding set having at least three stator windings.

[0011] The drive system further includes a control unit that is configured and constructed such that during operation, the at least one rotor winding is acted upon by a first current signal and the stator winding is at least partially acted upon by different current phases of a multi-phase second current signal, thereby forming a rotating magnetic field for generating a torque acting on the rotor.

[0012] The drive system further includes at least one inverter. Current signals for loading multiple phases of the stator winding are provided based on the at least one inverter.

[0013] Furthermore, the drive system includes at least one rectifier, which provides a DC signal.

[0014] The first current signal for loading the at least one rotor winding is based on at least a DC signal and a harmonic AC component provided by a rectifier. Harmonics of at least one current phase of the multi-phase current signal are reduced based on loading the at least one harmonic AC component onto the at least one rotor winding, the harmonics being caused by magnetic coupling occurring during operation between the at least one rotor winding and the stator winding.

[0015] The drive system may further include an additional inverter, based on which a harmonic AC component is provided for loading the at least one rotor winding. Alternatively, the at least one harmonic AC component may also be provided by an inverter that also provides a multi-phase current signal for loading the stator winding.

[0016] During operation, the rotor rotates relative to the stator about the axis of rotation at a specific rotational frequency. Harmonics of the rotor frequency that are multiple integer multiples of the rotational frequency and / or the rotating field can cause harmonics (resonant vibration currents) in the supply lines (current phases) of the stator winding due to magnetic coupling and the associated low impedance. These harmonics (resonant vibration currents) can cause peak loads. This has the following consequences: on the one hand, the components involved (such as the inverter, stator winding, supply lines) must withstand additional loads (such as increased maximum current amplitudes), and on the other hand, the maximum torque provided by the motor is reduced. This is because, in order to avoid damage and / or premature wear of the relevant components, the machine cannot be permanently operated at the actual maximum rated power.

[0017] In the present case, the separate excitation of the rotor winding by the rectifier provides an additional degree of freedom for balancing the harmonics caused by the magnetic coupling in the current phases of the stator winding. This degree of freedom is missing in permanent magnet synchronous machines. Therefore, the current signal provided to the rotor winding can be adapted so that the harmonics in the current phases of the stator winding are balanced and / or reduced. The drive system constructed as described above allows: to provide at least one additional harmonic AC component (in addition to the DC component) in the current signal provided to the rotor winding, which is superimposed and / or compensated in a "destructive" manner with the harmonics caused by the magnetic coupling in the current phases of the stator winding, thereby at least reducing their adverse effects.

[0018] The at least one inverter and the at least one rectifier, as well as an optional additional inverter (providing at least one harmonic AC component), can be coupled to at least one regulating circuit via real-time communication. The at least one regulating circuit can be configured to determine the phase and / or amplitude of the at least one harmonic AC component, taking into account operating states of the rectifier and / or inverter and / or adjustments performed by a control unit, such that harmonics caused by magnetic coupling in at least one current phase of the multiphase current signal are reduced in amplitude. The at least one harmonic AC component can also be determined such that harmonics caused by magnetic coupling are substantially balanced.

[0019] In other words, the control circuit can be coupled to a suitable sensor that provides information about the momentarily occurring harmonics of at least one current phase of the multiphase current signal caused by magnetic coupling. Furthermore, the control circuit can be coupled to an inverter and a rectifier in order to additionally couple at least one harmonic AC component into the DC current provided by the rectifier to at least one rotor winding in real time. The at least one coupled-in harmonic AC component can be configured in phase and / or amplitude relative to the harmonics of at least one current phase caused by magnetic coupling such that, after interaction due to magnetic coupling within the synchronous machine, the harmonics of at least one current phase are reduced in amplitude in a "destructive" manner and / or substantially equalized. The control circuit can also include additional control functions or control circuits, in particular, control by a control unit that can be used to determine the current phase based on a comparison of the actual current present in the motor with a rated current determined by the desired torque and / or based on the angular position of the rotor relative to the stator and / or the rotor's speed. The control circuit which determines the amplitude and / or phase of the harmonic AC component can therefore be coupled in particular to a conventional exciter control circuit and / or an inverter current controller and take their respective controls into account.

[0020] In the present context, a real-time communication device can be understood as a communication structure, bus system, or the like that allows for regulation such that the sampling rate is shorter than the rotor cycle time, which is determined by the rotational frequency. In particular, the sampling rate can be at least 10 times, more particularly 100 times, and even more particularly 1000 times, less than the rotor cycle time. Real-time communication also allows for rapid regulation such that the remaining, usually variable, variables of the synchronous machine can be assumed to be constant within the time interval determined by the sampling rate of the real-time communication. Harmonic AC components can thus be advantageously coupled in, reducing or equalizing harmonics caused by magnetic coupling without causing significant changes to the latter in the intervening time.

[0021] The inverter, rectifier, and control circuit can also be configured to provide multiple harmonic AC components. The at least one rotor winding can be loaded with multiple harmonic AC components of corresponding amplitudes and / or phases, so that the harmonics caused by magnetic coupling are reduced in amplitude and / or substantially equalized for each current phase of the multi-phase current signal (i.e., for each stator winding). Since each stator winding is loaded with a different current phase, the adverse effects of magnetic coupling can be reduced and / or equalized for each stator winding. To this end, in particular, multiple inverters and / or control circuits of the corresponding type can be provided. Alternatively, the inverter and / or control circuit can also be configured as a multi-phase system, i.e., so that the advantages described can be provided by the individual components for all current phases in a corresponding manner. Consequently, despite increasing the number of windings (which generally allows for an increase in the power output of the motor), power losses can be reduced. Furthermore, the load on the involved components is reduced.

[0022] The at least one harmonic AC component can have a first frequency. The second frequency of the fundamental frequency can be based on the rotational frequency of the rotor and / or the rotating field. The first frequency can be a multiple integer multiple of the second frequency. Since the synchronous machine in the present case includes a stator having at least two three-phase stator winding sets, parasitic harmonics caused by magnetic coupling in the current phases of the stator windings can in particular be harmonics of the fundamental frequency. To compensate for this, the harmonic AC component provided for the compensation must also have a frequency corresponding to a multiple of the fundamental frequency.

[0023] In particular, the frequency of the at least one harmonic AC component may correspond to the frequency of the 4th or 6th order harmonics. Thus, 5th or 7th order stator-side harmonics may be compensated. Consequently, the achievable modulation index may be advantageously increased, thereby also increasing the machine output power (maximum torque that can be provided).

[0024] The control unit can apply three-phase current to the stator winding sets during operation, i.e., apply individual current phases of the three-phase current. Different current phases of the three-phase current can be applied to the stator windings of the respective stator winding sets. The number of current phases can be at least six.

[0025] In the present case, the three-phase current must be understood as a vector with multiple components. The three-phase current can be provided by a corresponding power supply with three-phase components (lu, lv, lw). It can then be transformed into a stator-fixed and decoupled current with corresponding components by Clarke transformation. The components ld (torque forming component) and lq (flux forming component) can then be determined using Park transformation. According to the d / q transformation, ld and lq usually form components orthogonal to each other to describe the three-phase current, wherein the d / q coordinate system rotates with the rotor according to the rotation frequency of the rotor. For a speed that is constant over time, the rotating field can be described in the form of two variables d and q that are constant over time.

[0026] The rotor may be circular. The stator may be circular. The stator may be arranged about the axis of rotation. The stator may be arranged such that an air gap is formed between the rotor and the stator.

[0027] The stator can have stator teeth. The stator teeth can generally be oriented toward the rotor. The stator windings of a stator winding set can be arranged on the stator teeth. The stator winding can have a corresponding number of windings so that a specific torque can be achieved. The stator windings of a stator winding set can have an angular offset of 120° relative to each other with respect to the circumference of the stator. With respect to the circumference of the stator, the first stator winding set can have a predetermined angular offset (angular offset), in particular 30°, with respect to the second stator winding set. Thus, each stator winding set can itself form a discrete, symmetrical winding distribution. The stator windings can, however, be distributed unevenly with respect to the circumference of the stator as a whole. The phase shift described in this way can make it possible to avoid odd-numbered harmonic vibrations (5th or 7th order) inside the stator. However, due to the magnetic coupling with the separately excited rotor winding, these can generally still be induced in the stator.

[0028] The 30° angular offset allows the stator windings to be paired in the circumferential direction, with each pair comprising a corresponding stator winding from a stator winding set. During operation, magnetic coupling can occur between all stator windings and the rotor winding of the motor, affecting the current phases of the corresponding stator windings and thereby generating harmonics. However, for corresponding odd-order rotor harmonics (5th or 7th order), the stator impedance (particularly large magnetic coupling and leakage inductance) can be very low, so such harmonics are likely caused by the separately excited rotor in the stator winding and its current phase. However, any harmonics that are still induced can be reduced and / or balanced based on at least one harmonic AC component that loads the rotor winding.

[0029] The rotor can preferably be designed as a squirrel-cage rotor. To this end, the rotor can have a plurality of rotor bars that are evenly arranged on the circumference and extend along the axis of rotation. The rotor bars can also be arranged spaced apart from one another in the circumferential direction.

[0030] Each stator winding set can be connected to a potential-free star point according to a star connection. The star points of different stator winding sets can be electrically separated from one another. In the present case, a star connection is understood to mean that the three phases of a respective stator winding set can be electrically connected to one another at one end. At the respective other end, the three phases of a stator winding set can be connected to a respective current phase of a control unit and / or inverter. Thus, each phase of a stator winding set can be connected to a phase of a three-phase current network.

[0031] In particular, the star point cannot be connected to ground potential. This design concept is achieved by currents canceling each other out within the star point. This significantly reduces the manufacturing and wiring complexity of the motor. This ensures that the sum of all currents occurring within the connected stator winding sets is zero, and harmonics with orders corresponding to multiples of 3 do not occur.

[0032] In conjunction with the at least one inverter and / or the inverter control circuit, the control unit can be configured to set a predetermined frequency and / or amplitude of an applied multiphase current. To this end, the inverter can optionally include corresponding current regulators for each current phase of the multiphase current signal. In particular, three-phase current can be applied. In the present context, "applied" generally means energizing the stator winding with a multiphase current, particularly a three-phase current. The control unit can include a data acquisition unit. The control unit and / or inverter with the optional current regulator can also include switching elements by which the loading of the stator winding can be determined. The switching elements can be part of one or more inverters and / or current regulators and can be considered to belong to the control unit. In particular, the control unit can be configured to specify the start and stop times for loading the stator winding with current (three-phase current). The control unit can be configured to control the loading of the stator winding with current based on the angular position of the rotor relative to the stator. To this end, the motor can include a position transmitter or similar sensor by which the angular position of the rotor relative to the stator can be determined. The position transmitter or similar sensor can be coupled to the control unit or can be part of it.

[0033] The control circuit for determining the at least one harmonic AC component can then also be configured, in particular, to take the rotor position into account when determining the harmonic AC component. In other words, the harmonic AC component can be coupled into the current signal acting on the at least one rotor winding, thereby also achieving the desired compensation of the harmonics in the current phases. Alternatively, the phase of the at least one harmonic AC component can be adapted accordingly.

[0034] The electric machine may also include, in particular, a sensor by means of which coupling occurring in the electric machine between the first and second stator windings and / or the rotor winding can be determined. Alternatively or additionally, a sensor may also be provided to detect harmonics caused by the magnetic coupling. The control unit, and in particular the control circuit, may then be configured to take the detected harmonics into account when determining at least one corresponding harmonic AC component.

[0035] Because the electric motor can, in particular, have two stator winding sets, each with three stator windings, the inverter can preferably be two three-phase inverters, which can be connected on the input side to a DC intermediate circuit in the motor vehicle and / or to the vehicle's battery. The DC intermediate circuit and / or the battery can be used to supply energy to the electric motor. On the output side, the inverter can each be coupled to an optional current regulator, via which the amplitude of the three-phase current can be adjusted. In this regard, the inverter can be configured to provide a corresponding control voltage for amplitude adjustment, which can be performed by the current regulator.

[0036] The rotating magnetic field can extend radially within the air gap, i.e., in the radial or counter-radial direction. In the circumferential direction, i.e., in the direction of rotor rotation, the rotating magnetic field can have a distribution in the form of a rectangular step signal, which can be approximated by superimposing a fundamental sine wave with sine harmonics. In this regard, a Fourier series expansion can be used to approximate the distribution of the rotating magnetic field as a fundamental sine wave and a certain number of odd-order sine harmonics.

[0037] Therefore, in the present case, the consideration of the rotating magnetic field as a superposition of a fundamental sinusoidal wave and sinusoidal harmonics can represent the rotating magnetic field as a torque-generating factor within the electric machine. This approximation based on the rotating magnetic field can thus allow the control unit to achieve an optimized distribution of the rotating magnetic field and, thus, optimized torque generation by advantageously energizing the stator winding set. Simultaneously, parasitic harmonics generated by the magnetic coupling between the stator winding and at least one rotor winding of the electric machine can be reduced in amplitude and / or even substantially equalized by feeding harmonic AC signal components, which are appropriately adapted in phase and amplitude, into the current signal used to load the rotor winding.

[0038] However, the motor can also be operated as a synchronous motor, in which case the frequency of the rotor and the speed of the rotating magnetic field can be identical.

[0039] The inverter for providing multi-phase current signals may be arranged in the form of a full-bridge DC-DC converter, which may include diagonal active switching elements.

[0040] An inverter with an optional current regulator can also be designed so that the frequency and / or amplitude of the individual currents of the stator winding sets can be adjusted during motor operation so that the rotating field distribution approximated by the corresponding waves described above can be obtained. The adjustment of the amplitude and / or frequency can be achieved, for example, by controlling the control signals of the semiconductor switching elements inside the inverter. In the present case, the control signals can be provided by the control unit, for example. To this end, for example, the different current values ​​required for adjusting a specific operating mode can be stored for each phase in the control unit, in particular according to the current driving situation, such as the current load requirements. The phase current values ​​required for the corresponding operating mode can be determined, for example, based on simulations using commercially available programs, especially in the context of developing this type of machine. The phase current values ​​determined in this way can then be read into the memory of the control unit, for example for the corresponding motor vehicle.

[0041] During motor operation, the current actual phase current can be detected. To set the operating mode, the phase current values ​​stored for the relevant operating mode can preferably be set by an inverter with an optional current regulator, i.e., the respective phases are charged with the corresponding current values. The phase currents can be set, for example, using a setpoint / actual value comparison, where the current phase current is detected and adjusted to the desired value by the respective inverter. Thus, regulation is performed according to the desired value. The desired rotating field distribution can then be set by adaptively energizing the stator winding set, where parasitic harmonics generated by the magnetic coupling are balanced or at least weakened.

[0042] Alternatively or additionally, the intermediate circuits of the inverters can be connected to one another in order to achieve a more precise synchronization of the energization of the stator winding sets.

[0043] According to another aspect, an electrically driven vehicle is provided, comprising a drive system as described above. Within the meaning of the present invention, electrically driven vehicles may include, in particular, land vehicles, i.e., in particular electric scooters, electric kickboards, two-wheeled vehicles, motorcycles, three-wheeled vehicles, three-wheeled motorcycles, four-wheeled vehicles, off-road and road vehicles, such as passenger cars, buses, trucks and other commercial vehicles, rail vehicles (trains), as well as water vehicles (ships) and air vehicles, such as helicopters, multi-rotors, propeller planes, and jet aircraft, which have at least one electric motor for propelling the vehicle. The vehicle may be manned or unmanned. In addition to pure electric vehicles (BEVs), it may also include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell vehicles (FCHVs). BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A simplified schematic diagram showing the equivalent circuit diagram of the drive system,

[0045] Figure 2 a simplified schematic diagram showing an equivalent circuit diagram of an electric machine with stator windings, and

[0046] Figure 3 A simplified schematic diagram of two inverters is shown. DETAILED DESCRIPTION

[0047] Figure 1 A simplified schematic diagram of an equivalent circuit diagram of the drive system 50 is shown. Here, the overall structure of the drive system 50 is first described. The drive system 50 includes a voltage source 152, a control unit 90, a regulating circuit 95, an electric motor 100 having a rotor 102 and a stator 104, a rectifier 150, a first inverter 160, and a second inverter 165. The first inverter 160 and the second inverter 165 can also be combined into a single inverter. The rotor 102 includes a separately excited rotor winding. The stator 104 includes two three-phase stator winding sets, each having three stator windings 110. At least the inverter 165 is multi-phase.

[0048] Voltage source 152 may be, for example, a battery of an electrically drivable vehicle, ie, a DC voltage source. Voltage source 152 is (optionally) not considered to be part of drive system 50 and is therefore illustrated with a dashed line.

[0049] The rectifier 150 is coupled to a voltage source 152, or at least a corresponding DC voltage is provided to the rectifier 150 on the input side. On the output side, the rectifier 150 is coupled not only to the rotor 102 of the motor 100 and the first inverter 160, but also to the second inverter 165. The first inverter 160 is also coupled to the rotor 102 of the motor 100 on the output side. The DC current output by the rectifier 150 for the rotor winding of the rotor 102 is combined with the harmonic AC component provided by the first inverter 160 via a coupling element 161 to form the total current provided by the rotor winding of the rotor 102. In this regard, the DC current provided by the rectifier 150 for the rotor winding is modified by the corresponding AC current (harmonic AC component) provided by the first inverter 160.

[0050] The second inverter 165 provides multi-phase current signals to the stator winding 110 of the stator 104 .

[0051] The control unit 90 is coupled to at least the rectifier 150, the second inverter 165 and the motor 100. The control unit 90 is configured to design the multi-phase current signal provided by the second inverter 165 to the stator winding 110 so that the stator winding 110 is loaded with current phases of corresponding amplitude and phase, so that the desired torque is achieved by the motor 100. This regulation of the control unit can be based on a comparison of actual current / rated current. The control unit 90 can be configured to take into account the magnetic coupling between the stator windings 110 in the regulation related only to the stator winding 110. The rated current of the individual current phases can be stored in a memory according to the desired output power. The second inverter 165 can optionally have a corresponding current regulator in order to adapt, in particular, the phase and / or amplitude of the provided current phase.

[0052] The magnetic coupling between the rotor 102 and the stator 104 of the electric machine (more precisely, between their windings) may result in harmonics being generated by the rotor 102 in the current phases of the stator windings 110 .

[0053] The control circuit 95 is therefore coupled to the control unit 90, the rectifier 150, the first inverter 160, the second inverter 165, and the electric machine 100 via real-time communication. The control circuit 95 can obtain information about the order, phase, and amplitude of harmonics induced in the current phases of the stator winding 110 based on corresponding sensors. The control circuit 95 then considers the time-dependent control states of the rectifier 150, the first inverter 160, the second inverter 165, and optionally the control unit 90 to determine a harmonic AC component so that the harmonics induced in the current phases of the stator winding 110 can be reduced and / or balanced. In other words, the current provided to the rotor winding of the rotor 102 is modified by the AC component so that, due to the magnetic coupling with the stator winding 110 within the electric machine 100, it effectively causes no harmonics (or only harmonics of reduced amplitude) in the current phases of the stator winding 110. In order to be able to adapt the harmonic AC components provided by the first converter 160 accordingly in terms of phase and amplitude, the first converter can optionally have a current regulator.

[0054] When determining the harmonic AC components, the regulation circuit 95 can also take into account the regulation of the multi-phase current signals by the control unit 90. The regulation circuit 95 can also be considered to belong to the control unit.

[0055] The current regulators of the inverters 160 , 165 may include corresponding power switches, in particular semiconductor transistors, in order to provide a current of corresponding amplitude.

[0056] Figure 2 A simplified schematic diagram of an equivalent circuit diagram of an electric machine 100 having six stator windings 110 is shown.

[0057] In this embodiment, the stator 104 includes two stator winding sets, each of which includes three stator windings 110. For each stator winding set, the three stator windings 110 are arranged in the circumferential direction of the stator 104 with an angular offset of 120°. The two stator winding sets in turn have an angular offset 112, which in the present case is 30°. The stator windings of each stator winding set are generally arranged according to a star connection 130. This means that the three stator windings 110 of the first stator winding set are connected together at a first star point M1. The respective other ends of the stator windings 110 of the first stator winding set are coupled to an inverter 165a and a corresponding current regulator, as described below, and are loaded by the current phases U1', W1', and V1'. Similarly, the three stator windings 110 of the second stator winding set are connected together at a second star point M2, and their respective other ends are coupled to another inverter 165b and corresponding current regulators so that they are loaded by current phases U2', W2', and V2'. Similar to the second inverter 165 described previously, the two inverters 165a and 165b together provide multi-phase current signals for the stator windings.

[0058] By arranging the stator windings 110 in corresponding, but offset, stator winding sets, three stator winding pairs 120 are generated, each comprising a stator winding from a stator winding set. For example, stator winding pair 120a comprises a first stator winding 110a from a first stator winding set and a first stator winding 110b from a second stator winding set. The specific arrangement of the first stator winding 110a and the second stator winding 110b of the first stator winding pair 120a results in a particularly strong magnetic coupling between these stator windings within the electric machine 100. This magnetic coupling leads to leakage inductance. Consequently, a relatively small voltage difference between the two stator windings 110, 110b of the stator winding pair 120a results in relatively high current fluctuations in the respective other stator winding of the stator winding pair 120a. Current variations can be particularly strongly influenced in this manner. The control unit 90 takes this magnetic coupling between the stator windings 110 into account when determining and providing the current phases according to the second inverter 165.

[0059] In the present case, the three-phase current of the stator winding set is understood to be a vector current. Starting from the second inverter 165 with a current regulator coupled on the output side, this vector current includes current components U1', V1', W1' and U2', V2', W2'. These current components are modified by the current regulator to enable phase and / or amplitude adaptation. In this regard, the individual current components can be considered as different phases of the corresponding three-phase current.

[0060] During operation, the rotor 102 rotates around the axis of rotation at a specific rotational frequency. In addition to the previously described magnetic coupling of the stator winding 110, there is also a magnetic coupling of the stator winding 110 to at least one rotor winding. As a result, harmonics can be induced in the current phases of the stator winding 110 via the rotor winding. The frequencies of these harmonics are multiple integer multiples of the rotational frequency of the rotor / rotating field. Due to the geometry of the stator 104, i.e. the specific design of two three-phase stator winding sets with an angular offset of 30°, in particular harmonics of the 5th and / or 7th order can be induced. These harmonics can lead to current peaks, which lead to increased power losses and have a negative impact on the maximum achievable torque. In addition, this causes an increased load on the components involved, which reduces their service life. Therefore, as previously mentioned with reference to Figure 1 As described, these harmonics are reduced and / or balanced by loading the rotor windings with corresponding harmonic AC components.

[0061] Figure 3 A simplified schematic diagram of two inverters 165a, 165b of a drive system 50 is shown. The two inverters 165a, 165b are identical in their overall structure and function and are used to provide current phases of a multi-phase current signal. Alternatively, the drive system 50 can also have only one single inverter 165, as long as it outputs the required number of current phases.

[0062] The first inverter 165a is coupled to a DC voltage source 152 on the input side, via which a DC voltage is supplied to the inverter 165a. The inverter 165a then comprises, in a known manner, a capacitor 167 and switching elements 168, in particular semiconductor switching elements, as well as a center tap 169, in order to provide an AC voltage on the output side. In the present case, the first inverter 165a is configured to provide AC voltages that generally correspond to the current phases U1, V1, and W1. These AC voltages are output on the output side to corresponding current regulators, which adapt them in terms of phase and amplitude and then use them to load the stator windings 110 of the first stator winding set. The current regulators thus provide the corresponding current phases U1', V1', and W1' based on the AC voltages provided by the first inverter 165a. The current regulators are used to enable a compensating regulation of the actual current based on a comparison of the actual current present in the electric motor 100 with a rated current corresponding to the desired torque, in order to compensate for the corresponding discrepancies. In this respect, the current regulator has an influence, in particular, on the phase position and the amplitude of the current phases U1 ′, V1 ′, W1 ′.

[0063] In a corresponding manner, the second inverter 165b is configured to provide an AC voltage that is processed by a corresponding current regulator to provide the current phases U2', V2', W2'. A corresponding regulation is also envisaged here to compensate for the difference between the actual current in the motor 100 and the rated current corresponding to the desired torque.

Claims

1. A drive system (50), comprising: - an electric motor (100) configured as a synchronous motor and comprising: a rotor (102) configured to rotate about a rotation axis and having at least one separately excited rotor winding, and at least one stator (104) having at least two stator winding sets, each stator winding set having at least three stator windings (110), a control unit (90) arranged and constructed such that during operation a first current signal is applied to the at least one rotor winding and during operation different current phases of a second multi-phase current signal are at least partially applied to the stator winding (110), thereby forming a rotating magnetic field for generating a torque acting on the rotor, - at least one inverter (165), for providing a multi-phase current signal for applying a current to the stator winding based on the at least one inverter, and - at least one rectifier (150) providing a DC signal, wherein the first current signal for applying the at least one rotor winding is based on at least a DC signal provided by the rectifier and a harmonic AC component, and Harmonics of at least one current phase of a multiphase current signal are reduced by applying the at least one harmonic AC component to the at least one rotor winding, the harmonics being caused by magnetic coupling occurring between the at least one rotor winding and a stator winding during operation.

2. The drive system (50) according to claim 1, wherein: The at least one inverter (165) and the at least one rectifier (150) are coupled to at least one regulating circuit (95) via real-time communication means, and the at least one regulating circuit is configured to determine the phase and / or amplitude of the at least one harmonic AC component so that the harmonics of at least one current phase of the multi-phase current signal caused by the magnetic coupling are reduced in amplitude, in particular balanced in amplitude.

3. The drive system (50) according to claim 2, wherein: The inverter (165), the rectifier (150) and the regulating circuit (95) are configured to load the at least one rotor winding with a plurality of harmonic AC components having corresponding amplitudes and / or phases, so that the harmonics caused by the magnetic coupling are reduced in amplitude, in particular balanced in amplitude, for each current phase of the multi-phase current signal.

4. A drive system (50) according to any one of the preceding claims, wherein: The at least one harmonic AC component has a first frequency, a second fundamental frequency is based on a rotational frequency of the rotor (102) and / or a rotating field, and the first frequency is a multiple of the second frequency.

5. The drive system (50) according to claim 4, wherein: The first frequency of the harmonic AC component corresponds to at least the fourth and / or sixth order harmonics.

6. A drive system (50) according to any one of the preceding claims, wherein: The control unit (90) applies different current phases (U1', V1', W1', U2', V2', W2') of a three-phase current to the stator winding (110) during operation, and the number of current phases is at least six.

7. A drive system (50) according to any one of the preceding claims, wherein: The stator windings (110) of one stator winding set are arranged to be offset by 120° relative to the rotation axis of the rotor (102), the at least two stator winding sets are arranged to be offset by 30°, and the two stator winding sets are configured to be electrically offset by 30°.

8. A drive system (50) according to any one of the preceding claims, wherein: The stator winding sets are each connected according to a star connection (130) with a potential-free star point (M1, M2), the star points of different stator winding sets being electrically separated from one another.

9. An electrically drivable vehicle comprising a drive system (50) according to any one of claims 1 to 8.

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