Electromagnetic Interference Filter

Abstract

The present invention relates to an electromagnetic interference (EMI) filter 100 having feeder side terminals L1-L3 for connection to a power supply S and load side terminals L'1-L'3 for connection to a load L. The EMI filter 100 includes a load side passive EMI filter stage 1 connected to the load side terminals L'1-L'3 and configured to suppress common mode noise and differential mode noise. The EMI filter 100 further includes a feeder side active EMI filter stage 3 connected to the feeder side terminals L1-L3 and configured to suppress differential mode noise, and an intermediate active EMI filter stage 2 between the load side passive EMI filter stage 1 and the feeder side active EMI filter stage 3 configured to suppress common mode noise. The present invention also relates to a method for manufacturing the EMI filter 100.

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic interference (EMI) filter for filtering common-mode noise and differential-mode noise, and to a method for manufacturing the EMI filter. [Background technology]

[0002] Electrical systems in industrial applications are becoming increasingly complex and include numerous components that generate or are susceptible to being disturbed by electromagnetic interference. Electric motors are often driven by electronic inverters that control motor speed and torque, for example, by generating waveforms with variable frequency and amplitude. These systems offer high efficiency but generate strong electromagnetic interference.

[0003] Switching power converters are used in electric and hybrid vehicles, as well as in other non-contact devices such as stationary drive motors, chargers, photovoltaic systems, lighting controls, computers, etc. In all these cases, the switching action of the converters is a source of electromagnetic interference that can affect the functioning of other electrical systems or exceed standard limits if the interference is not managed or attenuated. Electromagnetic interference is often referred to in the art and herein by the acronym EMI. Also, the term "noise" is frequently used to refer to electromagnetic interference, although these are not of a stochastic nature. This specification also uses the expression "noise" in this manner.

[0004] These electrical or electronic filters used to filter unwanted electromagnetic interference, called electromagnetic interference filters or EMI filters for short, are used in all areas of electrical engineering to improve reliability and adhere to existing standards. A well-designed filtering system is crucial to the performance of many complex electrical systems.

[0005] The use of passive low-pass LC filters is known, and such filters have proven effective in many devices. While passive solutions do not provide sufficient attenuation, they have limitations. One limitation of passive EMI filters is that the desired level of attenuation requires high-value capacitors and inductances. The size and cost of the resulting manufactured filter are primarily determined by these large components. In many devices, high-value capacitors cause high levels of current (leakage current) and reactive current to flow into the grounding system, both of which are undesirable and detrimental to system operation.

[0006] A significant reduction in the size of high value capacitors and inductances can be achieved by combining an EMI filter with an active filter stage. The combination of these two different filter technologies can significantly reduce size and cost.

[0007] Many, if not all, EMI filters known from the literature, combining passive and active filters, are optimized to attenuate common mode noise or differential mode noise.

[0008] U.S. Patent No. 10,476,464 discloses an EMI common-mode filter device having two LC filters connected in series, two transformers, and an active current control circuit. The transformer is provided solely for sensing common-mode current and inputting the cancellation current generated by the current control circuit. The common-mode filter is specifically designed to reduce common-mode noise.

[0009] The construction of such common mode filters is complex: active current control circuits provide attenuation only under certain operating conditions, and these LC filters are then constructed to provide part of the common mode filter function even if the current control circuit fails.

[0010] International Patent Application No. 2015177746 discloses an EMI active differential mode line filter having at least one passive filter stage that makes it possible to filter high frequency common mode noise, at least one current detection circuit that makes it possible to detect noise, and at least one waveform generation circuit that makes it possible to make the voltage obtained from the current detection circuit have the same waveform as the noise.

[0011] Furthermore, this publication discloses at least one power supply unit that generates the power required for the active filter, and at least one current amplifier circuit that transmits a signal generated by the active filter and having the same waveform as the noise on the conductor to the input of the current detection circuit. This filter, especially the passive filter stage, is large and provides insufficient attenuation of common-mode noise signals. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Patent No. 10,476,464 [Patent Document 2] International Publication No. 2015177746 Summary of the Invention [Problem to be solved by the invention]

[0013] One object of the present invention is to provide an EMI filter that is designed for filtering common-mode and differential-mode noise, preferably on both the feeder side and the load side, with high attenuation for both noise modes.

[0014] Another object of the present invention is to provide an EMI filter configured to filter common-mode and differential-mode noise, which has lower inductance and capacitance values ​​for passive components while also being reduced in size. This significantly reduces the amount of materials used, such as iron, copper, etc. As a result, the design is also more sustainable. Furthermore, the EMI filter is easier to manufacture than related conventional EMI filters known from the literature. A further object of the present invention is to provide an EMI filter configured to filter common-mode and differential-mode noise, which provides sufficient noise attenuation even at frequencies below 150 kHz. [Means for solving the problem]

[0015] According to the present invention, these problems are solved by the subject matter of the appended claims, and in particular by an EMI filter having a feeder side terminal for connection to a power supply device, a load side terminal for connection to a load device, a load side passive EMI filter stage connected to the load side terminal and configured to suppress common mode noise and differential mode noise, and a feeder side active EMI filter stage connected to the feeder side terminal and configured to suppress differential mode noise.

[0016] The dependent claims define important, beneficial, but non-essential features such as an active intermediate EMI filter stage between the load-side passive EMI filter stage and the feeder-side active MI filter stage configured to suppress common-mode noise, first and second inductive elements and a capacitive element in the load-side passive filter, a common-mode circuit sensor, e.g., a current transducer, in the intermediate stage activating a current amplifier that inputs a cancellation current into the feeder to cancel the common-mode noise current, and a differential transformer in the feeder unit activated by the voltage amplifier to generate an electromotive force in the feeder that cancels the EMI measured on the feeder. The differential transformer can be activated to cancel differential-mode noise and, if desired, common-mode noise.

[0017] The differential transformer has a configuration that matches the number of phases present in the feeder. In the important cases of three-phase and single-phase feeders, the differential transformer has three phases or a single phase. Preferably, the differential transformer has one magnetic core. To simplify assembly, it has proven advantageous to form the core of the differential transformer by two parallel magnetic elements that can be separated to connect the differential transformer to the feeder without cutting or moving the power conductors (which may be rigid busbars). It has proven advantageous to have an air gap between these core elements to avoid saturation of the material.

[0018] Preferably, the intermediate side active filter and the feeder side active filter are feedback filters in which an error signal (e.g., common-mode noise current or differential-mode voltage) is sensed on the feeder, amplified by a suitable amplifier, and input as a cancellation signal onto the feeder before the measurement point. Preferably, the gain of the amplifier is variable and automatically controlled by the slow servo circuit to keep the output within a desired range without overdriving the slow servo circuit.

[0019] In relation to an interference source connected to the load terminals of the filter, the filter stages are preferably designed so that the resonant frequency of the load-side passive EMI stage is lower or higher than the fundamental frequency of the interference, for example, two or three times higher. Additionally or alternatively, the filter stages are preferably designed so that the EMI filter does not have self-resonance. Additionally or alternatively, the filter stages are designed so that the resonant frequency of the load-side passive EMI stage does not affect the switching frequency of the load. The resonant frequency is determined by several factors. Important among these factors are the selection of inductance and capacitance and / or nonlinear elements of the load-side passive EMI stage. On the other hand, since the inductance and capacitance values ​​are relatively small, the resonant frequency of the load-side passive EMI stage is lower or higher than the resonant frequency of a passive EMI filter characterized by attenuation comparable to that of a hybrid filter. In important applications where the interference source is a switching power converter, the fundamental frequency can be considered as the carrier frequency of the converter.

[0020] The EMI filter, particularly the load-side passive EMI filter stage, can be configured to dampen or suppress the resonance.

[0021] Further advantages of the present invention can be seen from the following. [Brief explanation of the drawings]

[0022] [Figure 1] 1 illustrates a schematic representation of an EMI filter according to a preferred embodiment. [Figure 2a] 1 illustrates a possible configuration of a capacitive filter element having means for damping or suppressing oscillations according to one embodiment. [Figure 2b] 1 illustrates a possible configuration of a capacitive filter element having means for damping or suppressing oscillations according to one embodiment. [Figure 3] 1 illustrates a differential transformer according to one embodiment. [Figure 4] 1 illustrates a differential transformer according to one embodiment. [Figure 5] FIG. 10 is a control diagram of a current amplifier and / or a voltage amplifier according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] 1, an EMI filter 100 according to the present invention is inserted on a power supply line 150 (in this case, a three-phase line) between a load 300 and a power supply device 200. The filter is inserted on the power supply line by suitable conductive terminals or by connecting conductors L1, L2, and L3 on the power supply line side and conductors L1', L2', and L3' on the load side. The load 300, which may be a motor drive including a cable and an electric motor, generates common-mode noise and differential-mode noise.

[0024] Power supply 5 may be any type of power supply arranged to supply power to power supply side terminals L1, L2, L3. "Power supply side" or "load side" in this specification refers to the physical location and / or electrical connection node of a device relative to a location on power supply 150. Power supply side means that the location or electrical connection node on power supply 150 is closer to power supply S than to load L, while load side means that the location or electrical connection node is closer to load L than to power supply S.

[0025] The power supply 5 may supply DC or AC power, or single-phase or polyphase power. On the other hand, the load L may be any device that is arranged to receive power and conduct noise to the power supply line 150 when connected to the load terminals L1', L2', L3'. Devices that generate conducted EMI are well known, such as generators, power supplies, voltage regulators, oscillators, and chargers.

[0026] The EMI is conducted along the feed line and is gradually reduced or attenuated by different filter stages 1, 2, 3 while conducting towards the power supply side 200.

[0027] From the load side toward the power supply, the filter 100 first includes a load-side passive stage 1. Passive filter 1 handles the highest levels of noise with the largest bandwidth. Passive filter 1 attenuates the amplitude and reduces the bandwidth of noise attempting to reach subsequent stages. Preferably, the load-side passive EMI filter stage 1 is configured to simultaneously suppress common-mode and differential-mode noise.

[0028] In this description, "passive" refers to the configuration of capacitors, inductors and optional resistors that make up the passive EMI filter stage 1. A passive filter does not depend on an external power source and does not include active elements such as amplifier circuits.

[0029] The active filter stages 2, 3 following the passive EMI filter stage 1 on the load side do not need to deal with the entire noise dynamics and bandwidth because the passive filter stage 1 significantly attenuates the higher parts of the frequency range in particular. The active EMI filter stages 2, 3 can be designed to reduce the amplitude and bandwidth, and as a result the active EMI filter stages 2, 3 can be smaller and less costly.

[0030] On the other hand, the attenuation provided by the active filter stages 2 and 3 is added to the attenuation of the passive filter stage 1. Advantageously, the passive filters are not required to provide very high attenuation, but it is sufficient that the noise passing through the passive filter 1 is reduced to a level that the active filter stages 2 and 3 can tolerate. This is mutually beneficial, because the passive filter stage 1 can be designed for less attenuation, especially at low frequencies, and therefore without large inductors and capacitors.

[0031] Returning to the passive filter stage 1, in this embodiment the passive filter stage 1 comprises a first inductive filter element 4 and a second inductive filter element 5 inductively coupled to the feed line 150.

[0032] The first inductive filter element 4 may be a common mode inductor electrically connected to the feed line 150. More preferably, the first filter element 4 is provided by a single ferrite core element placed on the feed line 150 such that the ferrite core element provides common mode attenuation to noise on the feed line 150 by providing a common mode impedance.

[0033] The second inductive filter element 5 may have the same configuration as the first inductive filter element 4, possibly with a higher or different inductance value. Typical values ​​for the inductance of these elements are between 10 μH and 50 μH, although these configurations may be modified in accordance with the present application.

[0034] The passive filter stage 1 further includes a capacitive filter element 6 electrically connected to a feed line 150 between the first inductive filter element 4 and the second inductive filter element 5. The capacitive filter element 6 may have connectors for electrically connecting to the feed line 150 and to ground G.

[0035] The capacitive filter element 6 is configured to suppress common-mode and differential-mode noise on the feed line 150. As is known in the art, the capacitive filter element 6 may be arranged with multiple capacitors interconnected to provide a network of X-connected capacitors to attenuate differential EMI and Y-capacitors to bypass common-mode EMI towards the common potential node G.

[0036] Y capacitors are well known and are generally connected to ground G. A network of X capacitors is called a delta connected capacitor network, while a network of Y capacitors is known as a star connected capacitor network. Delta connected capacitor networks can be used to bypass differential mode noise, while star connected capacitor networks can be used to bypass common mode noise. Suitable configurations of capacitor networks are known from the literature.

[0037] 1 also shows a low-voltage power supply 12 connected to the capacitive filter element 6. This component is used to provide the low-level power supply V+ required by the active filter stages 2 and 3, in particular to the current amplifier circuit 9 and the voltage amplifier circuit 11. The power supply 12 may be usefully connected to the capacitor bank 6, but this is not essential; in fact it may be embodied by any suitable DC source of low voltage, for example ±10 V. The power supply 12 is not a functional part of the passive filter stage 1 and does not contribute directly to attenuating noise.

[0038] The passive filter stage 1 is shown as a low-pass "T" LC filter, but may have other configurations and may provide low-pass, band-pass or band-stop filter transfer functions. Most passive LC filters resonate at a specific frequency or at two or more frequencies. The resonances may be damped by appropriate dissipative elements such as resistors or varistors.

[0039] The feeder-side active EMI filter stage 3 is connected to the feeder-side terminals L1, L2, L3. The feeder-side active EMI filter stage 3 is arranged to suppress differential mode noise on the feeder 150. In the embodiment shown, the EMI filter 100 features an active intermediate EMI filter stage 2 on the feeder 150 between the passive stage 1 and the feeder-side active stage 3, which is configured to suppress common mode noise on this feeder 150.

[0040] Placing the active intermediate EMI filter stage 2 between the load-side passive EMI filter stage 1 and the feeder-side EMI filter stage 3 has the advantage that the feeder-side EMI filter stage 3 presents a high impedance to the power supply S. In this way, the EMI filter does not interfere with other devices sharing this power supply.

[0041] In one aspect of the invention, the resonant frequency or frequencies are designed taking into account the fundamental frequency of the electromagnetic interference generated by a load device connectable or connected to the load terminals L1', L2', L3'. In the context of this specification, even if the noise is not strictly periodic, as is often the case, the expression "fundamental frequency" should be read as the noise having the lowest frequency and / or the highest amplitude. In critical applications where the load is a switching converter, the fundamental frequency may be the switching frequency, also called the carrier frequency, of the converter.

[0042] The fundamental frequency may be in the range of 1 kHz to 200 kHz. In most applications, the carrier frequency may be in the range of 2 kHz to 20 kHz or in the range of 50 kHz to 200 kHz.

[0043] The load-side passive EMI filter stage 1 is configured so that it exhibits a resonant frequency that is smaller or larger than the fundamental frequency of the noise coming from the load L. Preferably, the resonant frequency differs from the fundamental frequency of the noise by at least a factor of two, or preferably by a factor of five. This minimizes ringing and oscillation in the EMI filter 100, significantly improving the performance of the filter 100 and eliminating or reducing the resistors that are often used to damp the oscillations. High impedance can be achieved by selecting small values ​​of L and C in the passive elements 4, 5, and 6, and attenuation decreases at low frequencies. This is not a drawback, since the attenuation at low frequencies is increased by the active stages 2 and 3. On the other hand, the active stages 2 and 3 are preferably designed for high frequencies as well.

[0044] In a further embodiment, the EMI filter 1 may be configured with a resonant frequency as described above, but alternatively or additionally, resonances stimulated by noise radiation of the load L may be damped or suppressed using associated means, preferably configured in the load-side passive EMI filter stage 1. Thus, the EMI filter 1 may be configured without exhibiting a resonant phenomenon, since any resulting resonance is sufficiently damped or suppressed. The measures combined with a special design for the resonant frequency make the EMI filter 1 operate robustly and stably even in environments exhibiting high noise levels.

[0045] Adding a means for attenuation dramatically increases the flexibility for designing the load-side passive EMI filter stage 1. The load-side passive EMI filter stage 1 can be designed to provide a "one size fits all" solution for all intended applications. Even when the load-side passive EMI filter stage 1 is coupled to a noise-radiating load L that radiates noise having a fundamental frequency close to the resonant frequency of the load-side passive EMI filter stage 1, the attenuation means prevents any resonance phenomena in the EMI filter 1. As a result, the load-side passive EMI filter stage 1 can be designed for a multitude of applications despite using one specific resonant frequency.

[0046] In the illustrated assumed example, energy flows from the power supply S towards the load L, but this is not a requirement of the present invention. The present invention may also be applied to power generation systems or motors with regenerative braking. In the present invention, the power supplied to the load L may be negative, instantaneous or continuous. In other words, the switching power converter may be configured as a unidirectional or bidirectional switching power converter.

[0047] Preferably, the active intermediate EMI filter stage 2 includes a common mode current sensor 8, e.g. a current transformer or shunt resistor, arranged to provide a common mode noise signal proportional to the common mode noise current circulating in the power supply line 150.

[0048] A current amplifier 9 is arranged to receive the common-mode noise signal and generates a noise-canceling current having the opposite sign to the noise current. The noise-canceling current is input to the feeder 150 to attenuate the common-mode noise current circulating in this feeder 150. The variation shown is a feedback configuration: the cancellation current is input before this sensor 8 (on the load side relative to the sensor). Feed-forward filters are also possible and fall within the scope of the invention.

[0049] In this embodiment, the feeder side active EMI filter stage 3 includes a voltage amplifier circuit 11. The input of this voltage amplifier circuit 11 is connected to the feeder line 150 and senses voltage noise on the line. Although not shown in Figure 1, it will be appreciated that the voltage developed on the line will be stepped down to an acceptable level for the amplifier input by a suitable voltage divider or protection circuit.

[0050] In contrast to the intermediate stage, which is configured to suppress common-mode noise, the feeder-side stage 3 is configured to suppress differential-mode noise and acts on polyphase signals if the feeder 150 is a polyphase feeder. Since common-mode noise is handled by the intermediate stage, the feeder-side stage handles only differential-mode noise. However, this is not a required feature of the invention, and the filter stage 1 may be configured to attenuate common-mode noise components as well.

[0051] The output of the voltage amplifier circuit 11 generates a cancellation voltage which is superimposed on the supply line voltage, thereby attenuating the noise. The filter of the present invention is also shown in a feedback configuration, although this is not required for the intermediate stages.

[0052] As shown, the amplifier output is preferably connected to the power supply line via a differential transformer 10. The amplifier circuit 11 inputs current into a pair of primary windings of the differential transformer 10, which induces an electromotive force by magnetic induction in a conductor of the power supply line 150 arranged as a secondary winding.

[0053] In order to attenuate the voltage noise present on the power supply line 150, a voltage or voltage signal having an opposite phase to the noise component flowing on the power supply line 150 is induced.

[0054] 2a shows a possible configuration of the capacitive filter element 6 for a further embodiment having means for damping or suppressing oscillations, i.e. capacitive discharge damping means 61 for damping or suppressing resonances. Three capacitors C X1 ..C X3 One end of each capacitor C is connected to each phase of the power supply line 150. X1 ..C X3 are connected together to form a starting point 63. A capacitive discharge damping means 61 is connected between the starting point 63 and ground G via a node 62.

[0055] FIG. 2b shows a possible configuration of the capacitive discharge damping means 61, which includes a first leg 64 and a second leg 66 connected between a node 62 and ground G, respectively.

[0056] The first branch 64 includes a first unidirectional conductor D1 and a first Y capacitor C Y1 The first circuit point 65 includes a first unidirectional conductor D1 and a first Y capacitor C Y1 The first unidirectional conductor D1 is disposed between the node 62 and the first Y capacitor C Y1 The forward direction of the first unidirectional conductor D1 is connected from the node 62 to the first capacitor C Y1 It exists up to or towards the ground.

[0057] The second branch 66 includes a second unidirectional conductor D2 and a second capacitor C Y2 The second circuit point 67 includes a second unidirectional conductor D2 and a second capacitor C Y2 The second unidirectional conductor D2 is arranged between the node 62 and the second capacitor C2. The forward direction of the second unidirectional conductor D2 is Y2 It exists up to or away from the ground.

[0058] First capacitor C Y1 and the second capacitor C Y2 acts as a Y capacitor.

[0059] A unidirectional conductor is defined as any component or group of components that has asymmetric conductivity, i.e., that conducts current better in the forward direction than in the reverse direction. Preferably, the unidirectional conductor allows for nearly complete current conduction in the forward direction and nearly all current blocking in the reverse direction. Preferably, the unidirectional conductors D1 and D2 are diodes.

[0060] A resistor R is connected between the first branch 64 and the second branch 66. Preferably, the resistor R is connected between the first circuit point 65 and the second circuit point 67.

[0061] The two unidirectional conductors D1 and D2 are connected to a first capacitor C Y1 receives only the charge of the first polarity (here, positive), and the second capacitor C Y2 is configured in two branches 64 and 66 to receive only charges of the second polarity (here, negative). Due to the unidirectional conductors D1 and D2, the capacitor C Y1 and C Y2 Charge from capacitor C cannot flow back to node 62. Y1 and C Y2 discharges across resistor R, reducing the time integral of that voltage and common-mode noise. Y1 and C Y2 ultimately reduces or prevents oscillations in the EMI filter 100, particularly in the load-side passive EMI filter stage 1, that may be stimulated by noise emissions of the load L having the fundamental frequency of this load L. The capacitive discharge damping means 61 exhibits a non-linear behavior. Furthermore, due to the configuration of the capacitive discharge damping means 61, this capacitive discharge damping means 61 is energy-saving compared to other solutions in the prior art.

[0062] 3 shows a possible embodiment of a differential transformer 10 suitable for the present invention. Preferably, the differential transformer has a magnetic core divided into two core elements 19a and 19b. Preferably, the magnetic core elements 19a and 19b are made of a soft magnetic material with low coercivity and low hysteresis loss at frequencies where noise is expected, such as manganese zinc ferrite, nickel zinc ferrite, or the like.

[0063] Each of the magnetic core elements 19a and 19b has a plurality of recesses capable of accommodating the conductive wires 15a, 15b, and 15c and the insulating material 20. In this example, each of the magnetic core elements 19a and 19b has three recesses corresponding to the three phases of the power supply line 150.

[0064] First coil element 17a, second coil element 17b, and third coil element 17c are provided on first magnetic core element 19a. Each of coil elements 17a, 17b, and 17c is made of a wire that is wound multiple times around first magnetic core element 19a and placed in one of multiple recesses of first magnetic core element 19a.

[0065] The wire may be coated with varnish to electrically insulate the multiple windings from one another. Coil elements 17a, 17b, and 17c may be electrically insulated from first magnetic core element 19a using insulating material (not shown). Insulating material may be disposed between coil elements 17a, 17b, and 17c and the surface of magnetic core element 19a.

[0066] First conductor 15a, second conductor 15b, and third conductor 15c are disposed in respective recesses of the plurality of recesses. Conductors 15a, 15b, and 15c may be part of a power supply line 150 and may be configured to carry main current and common-mode and / or current-mode noise between power supply S and load L, or between load L and power supply S. Electrical insulation may be provided on each of conductors 15a, 15b, and 15c.

[0067] Additionally or alternatively, as shown in FIG. 3, the conductors 15a, 15b, 15c are electrically insulated from the magnetic core elements 19a, 19b using insulating material 20.

[0068] The magnetic core elements 19a and 19b are arranged so that they surround the conductors 15a, 15b, and 15c of the power supply line 150. Furthermore, the magnetic core elements 19a and 19b are arranged so that they provide a closed magnetic path, i.e., the conductors 15a, 15b, and 15c of the power supply line 150 form a secondary winding.

[0069] Coil elements 17a, 17b, and 17c form a primary winding, and magnetic core elements 19a and 19b form a magnetic core 19. These elements are part of a transformer, i.e., part of differential transformer 10. Magnetic core element 19 may have an air gap 21 to linearize the inductance of differential transformer 10 and to avoid saturation, since the air gap 21 reduces the slope of the associated B / H loop.

[0070] Primary and secondary as used herein refer to the aspects of the differential transformer 10 where a varying magnetic flux is generated in the magnetic core element 19 .

[0071] 4 shows a differential transformer 10 having three conductors 15a, 15b, and 15c surrounded by a magnetic core element 19 and three coil elements 17a, 17b, and 17c that can be connected to a voltage amplifier circuit 11, according to one embodiment of an EMI filter 100. These three conductors 15a, 15b, and 15c are part of a power supply line 150.

[0072] 4 shows a differential transformer 10, a power feeder 150, and an EMI filter for a three-phase AC system. Alternatively, the power feeder 150 may be a single-phase or multi-phase AC line. Alternatively, the differential transformer 10 may be a single-phase or multi-phase transformer having a single magnetic core element 19 formed by a first magnetic core element 19a and a second magnetic core element 19b.

[0073] Arranging the magnetic core 19 with two magnetic core elements 19a, 19b of the differential transformer 10 has the advantage that the differential transformer 10 can be easily installed on an existing power feeder 150 having a plurality of conductors 15a, 15b, 15c. The differential transformer 10 can be assembled or crimped to the power feeder 150, so there is no need to cut or disassemble the power feeder 150. Therefore, top hat rail installation can be generally applied to the differential transformer 10.

[0074] 5 is a conceptual diagram of an active filter stage such as may be used in the intermediate stage 2 or line-side stage 3 of the present invention. The load L and the power supply S are connected by a power supply line 150, which is shown as a single line. Of course, the power supply line 150 may also be a polyphase power line.

[0075] The amplifier circuit 9, 11 receives a noise signal (which may be a voltage signal, a current signal, a common mode signal or a differential mode signal) proportional to the noise sensed at sensing point A on the power supply line 150. Sensing point A is located on the power supply side 200. The active filter stage is configured to input a cancellation signal to summing point B, which is located on the load side stage 300.

[0076] The active intermediate EMI filter stage 2 or the feeder side active EMI filter stage 3 includes an amplifier circuit 9, 11 which produces an output conceptually represented by a cascade of ideal gain stages K. The output may be variable and have a transfer function T. The amplifier 11, 9 between A and B constitutes a first feedback control loop LC1 which attenuates noise in a known manner.

[0077] The second control loop LC2 is used to adaptively control the gain K. The second control loop LC2 is sensitive to the noise level and reduces the gain K when the noise exceeds a predetermined range, to the extent that the amplifier circuits 9 and 11 are saturated. Under normal conditions, when the noise level is below a predetermined threshold, the second control loop LC2 is not activated and the gain K has its normal value.

[0078] When the noise exceeds a predetermined threshold, the gain K is adjusted according to a predefined gain control function K C In this embodiment, the gain control function may be a linear function with a clipped maximum value. This maximum value may be related to the maximum output of the amplifier circuit 9, 11, or this maximum value may be set by the input variable P.

[0079] When the load device L requires more power than specified, for example during an overload operating mode, the gain K may need to be reduced, in which case the filter according to the invention will operate consistently while avoiding saturation and oscillations, providing a means of damping in all circumstances.

[0080] The first control loop LC1 and the second control loop LC2 operate on different time scales. The transfer function T of the first control loop LC1 determines the attenuation bandwidth of the stage, and noise must require as wide an attenuation bandwidth as possible. The second control loop LC2 operates at a slower speed and may have a time constant of a few milliseconds.

[0081] The first control loop LC1 is configured to respond very quickly to the noise signal at sensing point A, while the second control loop LC2, which has a negative feedback loop, finds an appropriate operating point for the loop gain, so this slower speed of operation is beneficial.

[0082] This arrangement, with a fast control loop LC1 for attenuating noise and a slower servo loop for varying the feedback gain K based on the level of the noise, is beneficial in improving the stability of the active intermediate EMI filter stage 2 and the feeder side active EMI filter stage 3, especially when these are arranged with the amplifier circuits 9 and 11 as described above, respectively.

[0083] The above method also relates to a method for manufacturing the EMI filter 100, in particular the differential transformer 10.

[0084] The method for producing comprises: - providing a plurality of electrical leads 15a, 15b, 15c; - providing a first magnetic core element 19a and a second magnetic core element 19b; - placing the conductive wires 15a, 15b, 15c between the first magnetic core element 19a and the second magnetic core element 19b; - The step of integrating the first magnetic core element 19a and the second magnetic core element 19b is included.

[0085] "Integrated" means that the first magnetic core element 19a and the second magnetic core element 19b are brought as close to each other as necessary. This does not exclude that an air gap 21 may remain between the first magnetic core element 19a and the second magnetic core element 19b. These magnetic core elements 19a and 19b are arranged so that they provide a closed magnetic path.

[0086] The method further includes the step of fixing the core elements 19a, 19b. The core elements 19a, 19b may be fixed using a fixing material such as an adhesive or varnish. Additionally or alternatively, other means, such as a fixture, may be used to fix the core elements 19a, 19b and hold them in place. The core elements 19a, 19b may be placed in the housing after securing their relative positions.

[0087] The method also includes connecting the conductors 15a, 15b, 15c to load side terminals L1', L2', L3' of the primary side of the differential transformer 10 and to power supply side terminals L1, L2, L3 of the secondary side opposite the primary side of the differential transformer 10.

[0088] Preferably, the steps are processed in the above order, but may alternatively be performed in any different order: it may be possible to first connect the conductors 15a, 15b, 15c to the load terminals L'1, L'2, L'3 and the feeder terminals L1, L2, L3, then supply the remaining components, and in a next step close the magnetic circuit.

[0089] This is possible for the above embodiment because the differential transformer 10 comprises two single core elements 19a, 19b, while only one of the two core elements 19a, 19b comprises the coil elements 17a, 17b, 17c.

[0090] This allows the EMI filter 100 to be retrofitted to the feeder line 150 and eases the associated manufacturing process.

[0091] Although the above embodiments or features describe different aspects of the present invention, where technically possible and advantageous, these embodiments or features may be combined individually or in combination in one EMI filter 100. However, if desired, these embodiments or features may be implemented separately. The present application relates to the invention described in the claims, but may also include the following configurations as other aspects. 1. An electromagnetic interference (EMI) filter (100) having power supply side terminals (L1-L3) for connection to a power supply device (S) and load side terminals (L'1-L'3) for connection to a load device (L), The EMI filter (100) includes a load-side passive EMI filter stage (1) connected to the load-side terminals (L'1-L'3) and configured to suppress common-mode noise and differential-mode noise, and a feeder-side active EMI filter stage (3) connected to the feeder-side terminals (L1-L3) and configured to suppress differential-mode noise. 2. 10. The EMI filter (100) according to claim 1, comprising an active intermediate EMI filter stage (2) configured to suppress common mode noise between the load-side EMI filter stage (1) and the feeder-side EMI filter stage (3). 3. 3. The EMI filter (100) according to claim 1 or 2, wherein, in relation to a load device (L) that inputs noise having a fundamental frequency to a power supply line (150), the load-side passive EMI filter stage (1) exhibits a resonant frequency lower or higher than the fundamental frequency of the noise. 4. EMI filter (100) according to claim 3, wherein the resonant frequency of the load-side passive EMI filter stage (1) is at least two times, preferably five times, lower or higher than the fundamental frequency of the noise. 5. 5. The EMI filter (100) according to claim 3 or 4, wherein the load device (L) includes a switching power converter, and the fundamental frequency of the noise is the carrier frequency of the switching power converter. 6. 6. The EMI filter (100) according to any one of 2 to 5 above, wherein the load-side passive EMI filter stage (1) includes means configured to have a non-linear function for attenuating or suppressing oscillations. 7. EMI filter (100) according to claim 6, wherein the means is a capacitive discharge attenuation means (61) configured within a capacitive filter element (6) of the load-side passive EMI filter stage (1). 8. 8. The EMI filter (100) according to any one of 1 to 7 above, wherein the load-side passive EMI filter stage (1) includes a first inductive filter element (4) and a second inductive filter element (5), each of the plurality of inductive filter elements (4, 5) being inductively coupled to a power supply line (150) and configured to suppress common-mode noise, and further includes a capacitive filter element (6) electrically connected to the power supply line (150) and configured to suppress common-mode noise and differential-mode noise. 9. The EMI filter (100) according to claim 2, wherein the active intermediate EMI filter stage (2) includes a common mode current sensor (8) for generating a common mode signal related to common mode noise circulating in the power supply line (150), and a current amplifier (9) for receiving the common mode signal, the current amplifier (9) being configured to input a noise cancellation current into the power supply line (150). 10. 10. The EMI filter (100) according to any one of claims 1 to 9, wherein the feeder-side active EMI filter stage (3) comprises a voltage amplifier circuit (11) connected to the feeder (150), configured to receive a noise voltage via a differential transformer (10) inductively coupled to the feeder (150), and to supply a noise cancellation voltage to the feeder (150). 11. 11. The EMI filter (100) according to claim 10, wherein the noise cancellation voltage includes a differential mode component and / or a common mode component. 12. The differential transformer (10) one first magnetic core element (19a) and one second magnetic core element (19b); a plurality of individual coil elements (17a-17c), each of which is wound around at least one of the plurality of magnetic core elements; 12. The EMI filter (100) according to claim 10 or 11, wherein the magnetic core elements (19a, 19b) are arranged to surround the plurality of conductors (15a-15c) of the power supply line (150) to form a closed magnetic circuit. 13. The EMI filter (100) described in 12 above, wherein the power supply line (150) is a single-phase, three-phase, or polyphase AC line, and the differential transformer (10) is configured as a single-phase, three-phase, or polyphase transformer having one magnetic core (19) formed by the first magnetic core element (19a) and the second magnetic core element (19b). 14. The active intermediate EMI filter stage (2) and / or the feeder side active EMI filter stage (3) are connected to a first control loop (LC 1 ) and the second control loop (LC 2 an amplifier circuit (9, 11) having - the first control loop (LC 1 ) includes an amplifier module having a transfer function (T) and a gain function (K) for adjusting the gain of the amplifier module; - the second control loop (LC 2 ) is used to reduce the input signal (I S ) according to the first control loop (LC 1 a gain control function (K) configured to adjust the gain function (K) of C 14. The EMI filter (100) according to any one of 2 to 13 above, comprising: 15. The second control loop (LC 2 ) of the gain control function (K C ) is controlled by a linear function with an upper limit. 1 15. The EMI filter (100) according to claim 14, wherein the gain function (K) of the filter is adjusted. 16. The upper limit of the linear function is the gain control function (K C 16. The EMI filter (100) according to claim 15, wherein the peak threshold value (P) corresponds to the target value in the range of 1000 Hz to 1000 Hz. 17. The first control loop (LC 1 ) and the second control loop (LC 2 ) each have one time constant, and the second control loop (LC 2 The time constant of the first control loop (LC 1 17. The EMI filter (100) according to any one of the above 14 to 16, wherein the time constant is larger than the time constant of the filter (100). 18. A method for manufacturing the EMI filter (100) according to claim 10 or 11, - providing a plurality of electrical leads (15a-15c); - providing a first magnetic core element (19a) and a second magnetic core element (19b); - placing these conductive wires (15a-15c) between the first magnetic core element (19a) and the second magnetic core element (19b); - integrating the first magnetic core element (19a) and the second magnetic core element (19b) to provide a closed magnetic path; - fixing the core elements (19a, 19b); - connecting the conductors (15a-15c) to load terminals (L1'-L3') on the primary side of a differential transformer (10) and to feeder terminals (L1-L3) on the secondary side opposite the primary side of the differential transformer (10). [Explanation of symbols]

[0092] 1 Load-side passive EMI filter stage 2 Active intermediate EMI filter stages 3. Power line side active EMI filter stage 4. First inductive filter element 5 Second inductive filter element 6 Capacitive filter elements 8 Common Mode Current Sensors 9 Current amplifier circuit 10 Differential transformer 11 Voltage amplifier circuit 12 Low voltage power supply 15a 1st conductor 15b 2nd conductor 15c 3rd conductor 17a First coil element 17b Second coil element 17c Third coil element 19 Magnetic Core 19a First magnetic core element 19b Second magnetic core element 20 Insulating materials 21 Air Gap 61 Capacitive discharge damping means 62 nodes 63 Starting Point 64 First Branch 65 1st circuit point 66 Second Branch 67 2nd circuit point 100 EMI Filters 150 Feed line 200 Power supply side 300 Load device side A sensing point B Additional points C X1... C X3 X capacitor C Y1 ,C Y2 Y capacitor G Ground I S Input signal K-profit function K C Gain Control Function L Load or load device L1 1st feed line side terminal L2 2nd feed line side terminal L3 3rd feed line side terminal L1' First load terminal L2' Second load terminal L3' Third load terminal LC1 First Control Loop LC2 Second Control Loop P Peak threshold target value S Power supply T transfer function V+ low voltage

Claims

1. the electromagnetic interference filter has a power supply line side terminal for connection to a power supply device and a load side terminal for connection to a load device; the electromagnetic interference filter includes a load-side passive electromagnetic interference filter stage connected to the load-side terminal and configured to suppress common-mode noise, and a feeder-side electromagnetic interference filter stage connected to the feeder-side terminal and configured to suppress differential-mode noise, The load-side passive electromagnetic interference filter stage is configured to suppress differential mode noise and the feeder-side electromagnetic interference filter stage is a feeder-side active electromagnetic interference filter stage, an active intermediate electromagnetic interference filter stage configured to suppress common mode noise between the load-side passive electromagnetic interference filter stage and the feeder-side electromagnetic interference filter stage.

2. 2. The electromagnetic interference filter according to claim 1, wherein, in association with a load device that inputs noise having a fundamental frequency into a power supply line, the load-side passive electromagnetic interference filter stage exhibits a resonant frequency lower or higher than the fundamental frequency of the noise.

3. 3. The electromagnetic interference filter of claim 2, wherein the resonant frequency of the load-side passive electromagnetic interference filter stage is at least two or five times lower or higher than the fundamental frequency of the noise.

4. 3. The electromagnetic interference filter of claim 2, wherein the load-side passive electromagnetic interference filter stage includes a first inductive filter element and a second inductive filter element, each of the plurality of inductive filter elements being inductively coupled to a power supply line and each configured to suppress common-mode noise, and further includes a capacitive filter element electrically connected to the power supply line and configured to suppress common-mode noise and differential-mode noise.

5. 3. The electromagnetic interference filter of claim 2, wherein the active intermediate electromagnetic interference filter stage includes a common mode current sensor for generating a common mode signal related to common mode noise circulating in the power supply line, and a current amplifier for receiving the common mode signal, the current amplifier being configured to inject a noise cancellation current into the power supply line.

6. 3. The electromagnetic interference filter of claim 2, wherein the feeder-side active electromagnetic interference filter stage includes a voltage amplifier circuit connected to the feeder line and configured to receive a noise voltage via a differential transformer inductively coupled to the feeder line and to provide a noise cancellation voltage to the feeder line.

7. 7. The electromagnetic interference filter of claim 6, wherein the noise cancellation voltage includes a differential mode component.

8. The differential transformer is one first magnetic core element and one second magnetic core element; a plurality of individual coil elements, each of which is wound around at least one of said plurality of magnetic core elements; Electromagnetic interference filter according to claim 6, wherein said magnetic core elements are arranged to surround the conductors of said feed line to form a closed magnetic circuit.

9. 9. The electromagnetic interference filter according to claim 8, wherein the power supply line is a single-phase, three-phase, or polyphase AC line, and the differential transformer is configured as a single-phase, three-phase, or polyphase transformer having one magnetic core formed by the first magnetic core element and the second magnetic core element.

10. the intermediate active EMI filter stage and / or the feeder-side active EMI filter stage comprises an amplifier circuit with a first control loop and a second control loop, said first control loop includes an amplifier module having a transfer function and a gain function for adjusting the gain of said amplifier module; Electromagnetic interference filter according to claim 1, wherein the second control loop includes a gain control function configured to adjust the gain function of the first control loop depending on an input signal in order to avoid saturation in the amplifier circuit.

11. 11. The electromagnetic interference filter of claim 10, wherein the gain control function of the second control loop adjusts the gain function of the first control loop according to a linear function having an upper limit.

12. 12. The electromagnetic interference filter of claim 11, wherein the upper limit of the linear function corresponds to a peak threshold target in the gain control function.

13. 11. The electromagnetic interference filter of claim 10, wherein the first control loop and the second control loop each have a time constant, the time constant of the second control loop being greater than the time constant of the first control loop.

14. 9. A method for manufacturing an electromagnetic interference filter according to claim 8, comprising the steps of: - providing a plurality of conductors; - providing a first magnetic core element and a second magnetic core element; - placing these conductors between the first and second magnetic core elements; - combining the first and second magnetic core elements to provide a closed magnetic path; - fixing said core element; - connecting said conductors to a load terminal on the primary side of a differential transformer and to a feeder terminal on the secondary side opposite said primary side of said differential transformer.

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