Motor drive having a filter including a three-phase differential mode reactor with common mode damping

Abstract

A motor drive having a T-type filter, the filter having at least two three-phase differential mode reactors and three capacitors, wherein at least one of the three-phase differential mode reactors comprises an auxiliary coil (6) wound around three wound core elements (2.1, 2.2, 2.3), so that a common mode current is induced in the auxiliary coil (6).

Description

Technical Field

[0001] The present invention relates to a filter for combined common mode filtering and differential mode filtering of a motor drive. Background Art

[0002] Three-phase motor drive systems inherently generate common-mode noise currents that circulate throughout the drive train from the power supply to the motor. Common-mode noise currents typically have a fundamental period and a high-frequency ringing of 50kHz. It places a heating load on the reactor and conductors, and thus reduces their life. This also requires the reactor to be sized larger than necessary to withstand the common-mode currents. Common-mode noise currents also deplete the isolation of the motor, which can cause motor defects.

[0003] To reduce resonant ringing, bulky RC and RL damping techniques may be used, which require additional space, increase cost, and reduce overall system efficiency, especially for high power applications.

[0004] An RC damper is a series connection of a resistor and a capacitor between ground and, for example, a DC link, a motor cable or a motor. However, this requires complex, extended and bulky robust high voltage capacitors. In addition, additional ground capacitors may have other undesirable side effects.

[0005] DE 295 06 951 U1 proposes a current-compensated common-mode choke to filter the common-mode current. Likewise, this solution is cumbersome and requires a large, heavy and extended additional choke.

[0006] DE102011086112A1 discloses a two-phase differential mode reactor in one embodiment. The reactor comprises a core having two winding pins and a third pin having an auxiliary winding closed by a resistor. The third pin is arranged so that the common mode flux of the two phases is summed in the third pin so that the resistor in the auxiliary winding can damp the common mode noise current. However, this solution has the disadvantage that the third pin of the differential mode reactor core significantly increases the size of the reactor, especially when applied to a three-phase system.

[0007] All current solutions for reducing common-mode noise currents in motor drives are cumbersome.

[0008] US3863109 discloses a solution for detecting a short circuit directly in an inductor to avoid further damage in other system components. Therefore, the inductor has a sensing coil which detects deviations from a symmetrical flux distribution to detect such a short circuit in the inductor. When the flux distribution of the inductor becomes asymmetrical due to a short circuit in the inductor, the sensing coil is connected to an open relay. One embodiment discloses such a sensing coil for a three-phase reactor. However, the sensing coil does not detect the system common mode noise current, in particular does not reduce the system common mode noise current. Summary of the invention

[0009] The object of the invention is to find a simple, light and small solution for reducing common mode noise currents in a motor drive.

[0010] This object is achieved by the motor controller, the three-phase differential mode filter and the three-phase differential mode reactor according to the first aspect of the present invention.

[0011] By simply adding one auxiliary coil in the three-phase differential mode reactor, the common mode current of the system is significantly reduced. The auxiliary coil requires almost no additional space because it is wound around the core element that is already necessary for the three differential mode inductor coils. No additional core elements (like extra common mode core pins) are necessary. Therefore, the common mode current can be significantly reduced without increasing the size and / or weight of the reactor, filter and / or motor controller.

[0012] Further aspects of the invention relate to further exemplary embodiments of the invention.

[0013] In one embodiment, the auxiliary coil is arranged in the reactor of the filter or the motor controller with the largest inductance. The common mode current is significantly affected by the maximum inductance of the system. By adding the auxiliary coil with the maximum inductance, the common mode current can be most effectively reduced. It is not necessary to also include this coil in other smaller inductors (but it can obviously be included there as well).

[0014] In one embodiment, the auxiliary coil is arranged in a reactor of a filter in the power line on the side towards the connection point of the converter. Preferably, this reactor is also the largest reactor of the filter and / or of the power line between the motor and the power supply.

[0015] In one embodiment, the auxiliary coil is short-circuited so that the common mode current induced in the auxiliary coil circulates therein and creates an anti-common mode flux in the three wound core elements of the differential mode reactor, which creates an anti-common mode current in the corresponding three coils. This alone already significantly reduces the common mode current of the system. Surprisingly, a resistor (or other impedance element) for damping the common mode current in the auxiliary coil is not necessary. This avoids additional hot hot spots in the reactor.

[0016] In one embodiment, the auxiliary coil is short-circuited with an impedance. This allows to increase the common mode noise current damping effect. The impedance is preferably an ohmic resistor. However, the impedance can also or additionally be complex, like a capacitor or an inductor or a combination of those. The impedance or resistor is preferably a discrete component, but can also be a parasitic impedance or resistance of the auxiliary coil.

[0017] In one embodiment, the auxiliary coil is wound around the first, second and third core elements such that common mode noise currents above 1 kHz are damped. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will be better understood with the aid of the description of embodiments given as examples and illustrated by the accompanying drawings, in which:

[0019] Figure 1 An embodiment of a motor drive system is shown.

[0020] Figure 2 An embodiment of a filter for a motor controller of a motor drive system is shown.

[0021] Figure 3 An equivalent circuit of common mode current without common mode damping in differential mode reactors is shown.

[0022] Figure 4 An equivalent circuit of common mode current with common mode damping in a differential mode reactor is shown.

[0023] Figure 5 from Figure 6 The side view indicated in FIG. 5 shows a first embodiment of a three-phase differential mode reactor with common mode damping.

[0024] Figure 6 from Figure 5 The side view indicated in VI-VI shows a first embodiment of a three-phase differential mode reactor with common mode damping.

[0025] Figure 7 from Figure 8 The side view indicated in VII-VII shows a second embodiment of a three-phase differential mode reactor with common mode damping.

[0026] Figure 8 from Figure 7 The side views indicated in FIG. VIII-VIII show a second embodiment of a three-phase differential mode reactor with common mode damping.

[0027] Fig. 9 A third embodiment of a three-phase differential mode reactor with common mode damping is shown from a side view.

[0028] Fig.10 Along Fig. 9 The cross section indicated in Figure XX A third embodiment of a three-phase differential mode reactor with common mode damping is shown.

[0029] Fig.11 The common mode noise without the three-phase differential mode reactor with common mode damping is shown.

[0030] Fig.12 Common mode noise with three-phase differential mode reactors with common mode damping is shown. DETAILED DESCRIPTION

[0031] Figure 1 A motor drive system according to the present invention is shown. The motor drive system comprises a power source G, a motor controller and a motor M.

[0032] The power source G is any three-phase AC current source, such as a three-phase AC network. The power frequency is typically 50 Hz or 60 Hz, but other power frequencies are also possible.

[0033] The electric motor M is preferably a three-phase AC motor. The electric motor M is controlled and / or powered by a three-phase AC current or mains of a motor controller. Therefore, the motor controller is connected to the electric motor M via a three-phase conductor or power line 16. The term motor should also include a generator, which in principle is an electric motor operated in reverse. An example of such a motor drive system with a generator can be a wind turbine. The term motor should also include a motor / generator, which sometimes operates as a motor and sometimes operates as a generator (e.g. during braking).

[0034] The motor controller provides the necessary control and / or power to the electric motor M. In case a generator is used as the motor, the motor controller transfers the power from the generator M to the power supply network G.

[0035] The motor controller comprises an AC / AC converter 11 and (preferably in a filter 12) at least one three-phase differential mode reactor with common mode damping according to the invention.

[0036] The AC / AC converter 11 converts the mains AC current into the motor AC current and / or vice versa. The AC / AC converter preferably comprises a rectifier (AC to DC), a DC-link and an inverter (DC to AC). However, other AC / AC converters 11 can obviously be used. The AC / AC converter 11, in particular the inverter, is a common source of (common mode) noise.

[0037] Preferably, the motor controller comprises a three-phase differential mode filter 12. The filter 12 is arranged in the mains 15, 16 between the power source G and the motor M. Preferably, the filter 12 is arranged between the power source G and the AC / AC converter 11, i.e. between the power source side input of the motor controller and the AC / AC converter 11. However, in another embodiment, the filter 12 may also be arranged between the motor M and the AC / AC converter 11, i.e. between the motor side input of the motor controller and the AC / AC converter 11.

[0038] Figure 2 An embodiment of a filter 12 is shown. The filter 12 has a power supply side input and a motor side input connected by a three-phase conductor 15, which is configured to conduct three-phase AC power between a power supply G and a motor M or between the power supply side input and the motor side input, respectively. At a connection point 25 between the power supply side input and the motor side input, three capacitors 24 are connected to the conductor 15 in a star point and / or a delta connection. Figure 2The star point connection is shown. However, it is clear to those skilled in the art that the circuit can be equivalently changed to a corresponding delta connection without any change to the electrodynamic behavior. The filter 12 includes (preferably) one, (even more preferably) two and may also include three of the following three three-phase differential mode reactors 21, 22 and 23, wherein the first three-phase differential mode reactor 21 is arranged between the power supply side input and the connection point. The second three-phase differential mode reactor 22 is arranged between the motor side input and the connection point. The third three-phase differential mode reactor 23 is arranged to be in a star point and / or delta connection with the connection point 25 (together with the capacitor 24). If the filter 12 includes the third three-phase differential mode reactor 23 or other components in the star point and / or delta connection of the capacitor 24, a combined star point connection and delta connection are also possible. Other components may be resistors connected in parallel with the capacitor 24. The star point is preferably not connected to ground. However, in some filters, the star point may be connected to ground (directly or through other components, like another ground capacitor). The filter 12 having the above circuit or another circuit may be an LCL filter, a PHF filter, a line filter, a harmonic filter, an EMC filter, an input filter, an output filter. The LCL filter may be implemented with the first reactor 21 and the second reactor 22 (without the third reactor 23). The output filter may be implemented with the third reactor 23 and the second reactor 22 (without the first reactor 21).

[0039] The motor controller may have other filters like an EMC filter 13. The EMC filter 13 may be an LC filter with an inductor L in the mains. CM，F and capacitor C in the ground connection between the mains and ground CM，F An EMC filter is preferably arranged between the power source G and the AC / AC converter 11 .

[0040] The motor controller (preferably the filter 12) comprises a three-phase differential mode reactor with common mode damping, as described below with the aid of Figures 5 to 10 As described in the embodiment shown in . Preferably, a three-phase differential mode reactor with common mode damping is arranged in the conductor 15 or 16 between the power supply side input and the motor side input (and therefore preferably not in the third three-phase differential mode reactor 23). Preferably, the three-phase differential mode reactor with common mode damping corresponds to the first reactor 21 or the second reactor 22 of the filter 12. Preferably, the three-phase differential mode reactor with common mode damping corresponds to the first reactor 21 or the second reactor 22 of the filter 12 on the side of the converter relative to the connection point 25. Preferably, the three-phase differential mode reactor with common mode damping is the reactor of the motor controller or the filter 12 or the first reactor 21 and the second reactor 22 having the largest inductance.

[0041] Figure 5 and 6 A first embodiment of a three-phase differential mode reactor with common mode damping is shown. Figure 7 and 8 A second embodiment of a three-phase differential mode reactor with common mode damping is shown. Fig. 9 and 10 A third embodiment of a three-phase differential mode reactor with common mode damping is shown. The three-phase differential mode reactor with common mode damping comprises a first core element 2.1 and a first coil 1.1 for the first phase, a second core element 2.2 and a second coil 1.2 for the second phase, and a third core element 2.3 and a third coil 1.3 for the third phase.

[0042] The first coil 1.1 is wound around the first core element 2.1. The first coil 1.1 is configured to conduct a current of a first phase (preferably from a power source to a motor). Preferably, one end of the first coil 1.1 is connected to a first input terminal of the reactor, and the opposite end of the first coil 1.1 is connected to a first output terminal of the reactor. Thus, the current of the first phase can flow from the first input terminal through the first coil 1.1 to the first output terminal (or vice versa). The first coil 1.1 wound around the first core element 2.1 provides a first inductance of the reactor for the first phase.

[0043] The second coil 1.2 is wound around the second core element 2.2. The second coil 1.2 is configured to conduct the current of the second phase (preferably from the power supply to the motor). Preferably, one end of the second coil 1.2 is connected to the second input terminal of the inductor, and the opposite end of the second coil 1.2 is connected to the second output terminal of the inductor. The terms input and output should not indicate any direction of the current. Therefore, the current of the second phase can flow from the second input terminal through the second coil 1.2 to the second output terminal (or vice versa). The second coil 1.2 wound around the second core element 2.2 provides a second inductance of the inductor for the second phase.

[0044] The third coil 1.1 is wound around the third core element 2.1. The third coil 2.1 is configured to conduct the current of the third phase (preferably from the power supply to the motor). Preferably, one end of the third coil 1.1 is connected to the third input terminal of the inductor, and the opposite end of the third coil 1.1 is connected to the third output terminal of the inductor. The terms input and output should not indicate any direction of the current. Therefore, the current of the third phase can flow from the third input terminal through the third coil 1.1 to the third output terminal (or vice versa). The third coil 1.3 wound around the third core element 2.3 provides the third inductance of the inductor for the third phase.

[0045] Some terms will be clarified below. The terms "input terminal" and "output terminal" should not indicate any direction of the current. The term "terminal" is preferably a device for fixing a cable or conductor, like a clamp, a screw or a solder joint. However, the terminal can also be a continuous connection of a cable or conductor to a corresponding coil. The terms "common mode" and "differential mode" should be briefly explained. The current flowing in the three phases of the motor drive system, the motor controller, the filter 12 and / or the inductor consists of common mode current and differential mode current. "Differential mode current" is the current that sums up to zero in all phases. The power used by the AC current is the differential mode current. However, it is only expected to use the AC current at the power frequency of 50Hz or 60Hz. The remaining differential mode current is regarded as "differential mode noise current". Those currents appear especially at higher frequencies and are filtered using corresponding filters (like harmonic filters, EMC filters, input filters, etc.). The remaining currents that are not zero in total on the three phases are "common mode currents", which "travel" on the mains in a common direction (to the motor M or the power supply G). The common mode current then flows back to ground. Common mode current is generally undesirable and is also referred to as common mode noise current. Common mode noise current generally includes "common mode ringing noise current", includes higher harmonics of the common mode noise current and / or includes common mode noise current above 1 kilohertz (kHz).

[0046] The three core elements 2.1, 2.2 and 2.3 can be parts of the same core as shown in the third embodiment, or parts of separate cores as in the first and second embodiments. The use of three separate cores in the form of rings, as in the first and second embodiments, has been shown to be particularly advantageous for the inventive reactor with common-mode damping. The core in the form of rings is preferably closed and therefore has no air gaps. The outer and / or inner form of the ring is preferably circular (e.g. Figure 6 and 8 However, other ring forms are possible such as triangle, rectangle, n-angle, etc. The cross-sectional form of the ring is preferably as follows Figure 5 and 7, which is a rectangular shape shown in the figure (possibly with rounded edges). However, other forms of cross-section with a ring are also possible, like a circular cross-section (combined with a ring in the form of a circular ring to produce a torus). However, it is also possible to use other forms of separated cores as I-cores, C-cores, E-cores, EI cores, etc. The three core elements 2.1, 2.2 and 2.3 can also be parts of the same core as shown in the third embodiment, for example. Herein, each core element 2.1, 2.2, 2.3 corresponds to a winding column of the core. The three winding columns are connected by at least a first yoke. In the embodiment shown, the three winding columns are connected by a first yoke (connected to the winding pins without an air gap) and a second yoke (connected to the winding pins with an air gap). Obviously, many other designs of a common core for the three core elements 2.1, 2.2 and 2.3 are possible.

[0047] The three coils 1.1, 1.2, 1.3 are wound around the core elements 2.1, 2.2, 2.3 such that the first coil 1.1 wound around the first core element 2.1 damps the differential mode noise current in the first phase (i.e. flowing through the first coil 1.1), the second coil 1.2 wound around the second core element 2.2 damps the differential mode noise current in the second phase (i.e. flowing through the second coil 1.2), and the third coil 1.3 wound around the third core element 2.3 damps the differential mode noise current in the third phase (i.e. flowing through the third coil 1.3). The three coils 1.1, 1.2, 1.3 are wound around the three core elements 2.1, 2.2, 2.3 such that the first differential mode magnetic flux created by the differential mode current flowing through the first coil 1.1 is not compensated in the first core element 2.1 by the (second and third) differential mode fluxes created by the other two coils 1.2, 1.3 in the first core element 2.1 (contrary to a current compensated common mode choke). The same situation holds true for the second coil 1.2 and the third coil 1.3. Therefore, the first differential mode magnetic flux induces a first counter differential mode noise current in the first coil 1.1 to reduce the differential mode noise current flowing through the first coil 1.1.

[0048] According to the present invention, the three-phase differential mode reactor includes an auxiliary coil. Preferably, the auxiliary coil is wound around the first core element 2.1, the second core element 2.2 and the third core element 2.3, so that a common mode current flowing through the first phase, the second phase and the third phase is induced in the auxiliary coil. This can be achieved by a toroid or common coil 6 (in each loop of each winding of the toroid or common coil) surrounding all three core elements 2.1, 2.2, 2.3 as shown in the first and third embodiments, or by a combination of a first sub-auxiliary coil 6.1 wound around the first core element 2.1, a second sub-auxiliary coil 6.2 wound around the second core element 2.2 and a third sub-auxiliary coil 6.3 wound around the third core element 2.3 as shown in the second embodiment. The three sub-auxiliary coils 6.1, 6.2 and 6.3 are preferably connected in series with each other. The number of windings of the auxiliary coil (i.e. the toroid coil 6 or each sub-auxiliary coil 6.1, 6.2, 6.3) can be arbitrary, but preferably less than 10, preferably less than 5, preferably less than 3. Preferably, the number of windings of the auxiliary coil is at least one complete winding.

[0049] Preferably, the auxiliary coil 6 or 6.1, 6.2, 6.3 is wound around the first core element 2.1, the second core element 2.2 and the third core element 2.3 so that a first common mode flux created by the common mode current flowing through the first phase or the first coil 1.1, a second common mode flux created by the common mode current flowing through the second phase or the second coil 1.2 and a third common mode flux created by the common mode current flowing through the third phase or the third coil 1.3 induce a resulting (non-zero) common mode current in the auxiliary coil 6 or 6.1, 6.2, 6.3. Preferably, the same common mode current component is induced in the auxiliary coil 6 or 6.1, 6.2, 6.3 by each coil 1.1, 1.2 and 1.3. The auxiliary coil 6 or 6.1, 6.2, 6.3 is short-circuited. The common mode current induced in the auxiliary coils 6 or 6.1, 6.2, 6.3 creates an anti-common mode flux that is induced back in the three coils 1.1, 1.2, 1.3, where it compensates or damps the common mode current. The auxiliary coils 6 or 6.1, 6.2, 6.3 are wound around the positions of the first core element 2.1, the second core element 2.2 and the third core element 2.3, where the same common mode flux is created by the same common mode current flowing through the respective coils 1.1, 1.2, 1.3. For a core element in the form of a ring, this is around every position of the ring. Preferably, the auxiliary coils 6 or 6.1, 6.2, 6.3 are wound around the positions of the first core element 2.1, the second core element 2.2 and the third core element 2.3, where the respective common mode flux of the respective phase or coil is maximum and / or is not divided in a core flux path. For a core element in the form of a ring, this is around every position of the ring.

[0050] In an embodiment with the toroidal object coil 6, the first common mode flux, the second common mode flux and the third common mode flux enclosed together in the toroidal object coil 6 are summed or integrated into the generated common mode flux. Then, the generated common mode flux induces the generated common mode current in the toroidal object coil 6. The anti-common mode current in the toroidal object coil 6 creates an anti-common mode flux, which creates corresponding anti-common mode currents in the three coils 1.1, 1.2 and 1.3, which damp the common mode current in each coil 1.1, 1.2, 1.3. Each winding of the toroidal object coil 6 thus surrounds all three core elements 2.1, 2.2 and 2.3. The embodiment of the toroidal object coil 6 has the advantage that the construction of the existing differential mode three-phase reactor must not be changed. The toroidal object coil 6 can be simply added at the end of the manufacturing process, or even refurbished later. Preferably, the toroidal object coil 6 is isolated and / or kept in place by the packaging of the three-phase reactor.

[0051] In an embodiment with sub-auxiliary coils 6.1, 6.2, 6.3, a first common mode flux induces a first common mode current in the first sub-auxiliary coil 6.1, a second common mode flux induces a second common mode current in the second sub-auxiliary coil 6.2 and a third common mode flux induces a third common mode current in the third sub-auxiliary coil 6.3. The sub-auxiliary coils 6.1, 6.2, 6.3 are combined so that the first common mode current in the first sub-auxiliary coil 6.1, the second common mode current in the second sub-auxiliary coil 6.2 and the third common mode current in the third sub-auxiliary coil 6.3 are combined, preferably totaling to the resulting common current of the auxiliary coils 6.1, 6.2, 6.3. The generated common mode current in the auxiliary coils 6.1, 6.2, 6.3 then creates a first anti-common mode flux in the first core element 2.1 via the first sub-auxiliary coil 6.1, a second anti-common mode flux in the second core element 2.2 via the second sub-auxiliary coil 6.2, and a third anti-common mode flux in the third core element 2.3 via the third sub-auxiliary coil 6.3. The first anti-common mode flux induces a first anti-common mode current in the first coil 1.1 for damping the common mode current therein. The second anti-common mode flux induces a second anti-common mode current in the second coil 1.2 for damping the common mode current therein. The third anti-common mode flux induces a third anti-common mode current in the third coil 1.3 for damping the common mode current therein.

[0052] By closing or short-circuiting the auxiliary coil 6 or 6.1, 6.2, 6.3 on an impedance, the effect of common mode damping can be increased. The impedance is preferably an ohmic resistor. However, the impedance can also or additionally be complex, like a capacitor or an inductor or a combination of those. The impedance or resistor is preferably a discrete component, but can also be a parasitic impedance or resistance of the auxiliary coil. Discrete components have the disadvantage that it creates hot spots. It was found that the effect of common mode damping is strong enough without such a resistor.

[0053] Figure 3 The equivalent circuit of the common-mode current in a motor drive system without common-mode damping in a three-phase differential-mode reactor is shown. The common-mode current flows from the power supply G to the motor M through the three phases and back through the ground (or in the opposite direction). The behavior of the common-mode current is determined by the inductance L of the motor drive system. CM Its capacitance to ground C CM Limit. The capacitance to ground is, for example, the motor capacitance C CM，M , converter capacitance C CM，RI and EMC filter capacitor C CM，F ,like Figure 1 The common-mode noise damping factor of a motor drive system is proportional to

[0054]

[0055] Therefore, in the prior art, the large inductance of the differential mode filter leads to a small common mode damping factor. This leads in particular to common mode ringing noise currents in higher frequencies, which are Fig.11 is not damped as seen in . Fig.11 Common mode currents in the motor drive, in the filter 12 and / or in the reactor without common mode damping are shown.

[0056] Now, Figure 4 The effect of common-mode damping in a three-phase differential-mode reactor is shown in Figure 2. Reducing the effective common-mode inductance increases the common-mode noise damping factor by the following amount:

[0057]

[0058] Fig.12 1 shows the common mode currents in the motor drive, in the filter 12 and / or in the reactor with common mode damping. Fig.12 As seen in Fig.11 Therefore, a minimal change to the structure of the reactor by the auxiliary coil for damping common mode noise results in a significant reduction in the common mode ringing noise current.

[0059] A three-phase differential mode filter 12 and / or a three-phase differential mode reactor with common mode damping is described in a motor controller of a motor drive system. However, the three-phase differential mode filter 12 and / or the three-phase differential mode reactor with common mode damping can be used in any other controller or converter circuit. Preferably, such a controller or converter circuit includes at least one converter (e.g., an inverter) and at a three-phase differential mode filter 12 and / or a three-phase differential mode reactor with common mode damping. In this case, the power supply side input of the filter 12 or the reactor can generally be regarded as the first side input, and the motor or converter side input of the filter 12 or the reactor can generally be regarded as the second side input. The three-phase differential mode reactor is preferably used to filter differential mode noise current (within a specific frequency range), that is, to damp differential mode noise current. However, the three-phase differential mode reactor can also be used in other applications to (significantly) form or process differential mode current. Damping is a preferred form of forming or processing differential mode current. An alternative treatment may be an integral differential mode current.

Claims

1. A three-phase differential mode filter for a motor drive, comprising for each phase: A power supply side input, a motor side input, a conductor between the power supply side input and the motor side input for conducting a current of the motor drive between a power supply and a motor, a connection point in the conductor, wherein the filter comprises three capacitors connected to the connection point of the conductors of the three phases in a star point and / or a delta connection, wherein the filter comprises at least two of a first three-phase differential mode reactor between the power supply side input and the connection point, a second three-phase differential mode reactor between the motor side input and the connection point, and a third three-phase differential mode reactor connected to the connection point via a star point and / or a delta connection, wherein one of the at least two three-phase differential mode reactors is a common mode compensation three-phase differential mode reactor having the following characteristics: A first core element (2.1); A second core element (2.2); a third core element (2.3); a first coil (1.1) wound around the first core element (2.1) to conduct the current of the first phase and damp differential mode noise current in the first phase; a second coil (1.2) wound around the second core element (2.2) to conduct the current of the second phase and damp the differential mode noise current in the second phase; a third coil (1.3) wound around the third core element (2.3) to conduct the current of the third phase and damp differential mode noise current in the third phase; and The common-mode compensation three-phase differential-mode reactor comprises an auxiliary coil (6; 6.1, 6.2, 6.3) which is wound around the first core element (2.1), the second core element (2.2) and the third core element (2.3), so that common-mode currents in the first phase, the second phase and the third phase are induced in the auxiliary coil (6; 6.1, 6.2, 6.3), The auxiliary coil (6; 6.1, 6.2, 6.3) is wound around the first core element (2.1), the second core element (2.2) and the third core element (2.3), so that the differential mode currents of the first phase, the second phase and the third phase are in the auxiliary coil (6; 6.1, 6.2, and 6.3) cancel each other out.

2. The filter according to claim 1, wherein the common mode current through the first coil (1.1) creates a first common mode magnetic flux in the first core element (2.1), wherein the common mode current through the second coil (1.2) creates a second common mode magnetic flux in the second core element (2.2), wherein the common mode current through the third coil (1.3) creates a third common mode magnetic flux in the third core element (2.3), wherein the auxiliary coil (6; 6.1, 6.2, 6.3) are wound around the first core element (2.1), the second core element (2.2) and the third core element (2.3), so that the first, second and third common mode magnetic fluxes are in the auxiliary coil (6; 6.1, 6.2, 6.3) in total.

3. The filter according to claim 1 , wherein the first end of the auxiliary coil (6; 6.1, 6.2, 6.3) is directly connected to the auxiliary coil (6; 6.1, 6.2, 6.3) are connected to the second end.

4. A filter according to one of claims 1 to 2, wherein the auxiliary coil (6) comprises a toroidal coil (6) which is wound around the first core element (2.1), the second core element (2.2) and the third core element (2.3) so that it encloses the first core element (2.1), the second core element (2.2) and the third core element (2.3) in the same loop or coil.

5. A filter according to any one of claims 1 to 2, wherein the auxiliary coil comprises a first sub-auxiliary coil (6.1) wound around the first core element (2.1), a second sub-auxiliary coil (6.2) wound around the second core element (2.2), and a third sub-auxiliary coil (6.3) wound around the third core element (2.3), wherein the first end of the auxiliary coil corresponds to the first end of the first sub-auxiliary coil (6.1), wherein the second end of the first sub-auxiliary coil (6.1) is connected to the first end of the second sub-auxiliary coil (6.2), wherein the second end of the second sub-auxiliary coil (6.2) is connected to the first end of the third sub-auxiliary coil (6.3), and wherein the second end of the auxiliary coil corresponds to the second end of the third sub-auxiliary coil (6.3).

6. A filter according to one of claims 1 to 2, wherein the first core element (2.1) is a first winding pin of a three-phase core, the second core element (2.2) is a second winding pin of the three-phase core, and the third core element (2.3) is a third winding pin of the three-phase core, wherein the three-phase core includes at least one yoke connecting the first, second and third winding pins.

7. The filter according to one of claims 1 to 2, wherein the first core element (2.1), the second core element (2.2) and the third core element (2.3) are three separate cores. The filter according to claim 7 , wherein each of the three separate cores has a ring form.

9. The filter according to any one of claims 1 to 2, wherein the inductance of the common-mode compensation three-phase differential-mode reactor is greater than the inductance of any other three-phase differential-mode reactor of the filter.

10. A filter according to any one of claims 1 to 2, wherein the auxiliary coil (6; 6.1, 6.2, 6.3) is wound around the first core element (2.1), the second core element (2.2) and the third core element (2.3), so that the common mode current in the first phase, the second phase and the third phase is damped by the auxiliary coil (6; 6.1, 6.2, 6.3) in a frequency range above one kilohertz.

11. A motor controller comprising a filter according to any one of claims 1 to 2 and an AC-AC converter for converting the supply current into the motor current. 12 . The motor controller according to claim 11 , wherein the filter is arranged between a power supply side and the AC-AC converter.

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