Electromagnetic Interference Filters

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. In many cases, electromagnetic interference is denoted in the art and herein by the acronym EMI. Also, the term "noise" is frequently used to denote electromagnetic interference, although these are not of stochastic nature. This specification also uses the expression "noise" in this way.

[0004] These electrical or electronic filters used for 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] It is known to use passive low-pass LC filters, and such filters have proven effective in many devices. While passive solutions do not provide sufficient attenuation, they do 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 determined primarily by these large components. In many devices, high value capacitors cause high levels of current (leakage current) and reactive current to flow into the ground 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 result in significant reductions in size and cost.

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

[0008] US Patent No. 10476464 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 only to sense the common mode current and to input 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: the active current control circuit provides attenuation only under certain operating conditions, and these LC filters are then constructed to provide part of the common mode filter functionality even if the current control circuit fails.

[0010] International patent application WO2015177746 discloses an EMI active differential mode line filter having at least one passive filter stage making it possible to filter high frequency common mode noise, at least one current detection circuit making it possible for the noise to be detected, and at least one waveform generation circuit making it possible for the voltage obtained from the current detection circuit to have the same waveform as the noise.

[0011] Furthermore, this publication discloses at least one power supply unit generating the power required for the active filter, and at least one current amplifier circuit transmitting 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 poor attenuation for common mode noise signals. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Pat. No. 1,047,6464 [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 supply line 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 arranged for filtering common mode and differential mode noise, which has lower values ​​of inductance and capacitance for passive components, while at the same time being reduced in size. This allows a significant reduction in the amount of materials such as iron, copper, etc. used. 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 arranged for filtering common mode and differential mode noise, which attenuates noise sufficiently 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 attached claims, in particular by an EMI filter having a power supply 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 power supply side active EMI filter stage connected to the power supply side terminal and configured to suppress differential mode noise.

[0016] The dependent claims define important, useful, 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, a first and second inductive element 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 which inputs a compensation current into the feeder cancelling the common mode noise current, a differential transformer in the feeder unit activated by a voltage amplifier to generate an electromotive force in the feeder cancelling the EMI measured on the feeder, which can be activated to cancel differential mode noise and, if desired, common mode noise.

[0017] Said 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 the assembly, it has been found to be advantageous to form the core of the differential transformer by two parallel magnetic elements that can be separated to connect this differential transformer to the feeder without cutting or moving the power conductor (which may be a rigid busbar). An air gap between these core elements has been found to be advantageous 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 on 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 stages of the filter are preferably designed such that the resonant frequency of the passive EMI stage on the load side is smaller or larger than the fundamental frequency of the interference, for example two or three times higher. Additionally or alternatively, the stages of the filter are preferably designed such that the EMI filter has no self-resonance. Additionally or alternatively, the stages of the filter are designed such that the resonant frequency of the passive EMI stage on the load side 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 the inductance and capacitance and / or the nonlinear elements of the passive EMI stage on the load side. On the other hand, since the inductance and capacitance values ​​are relatively small, the resonant frequency of the passive EMI stage on the load side is smaller or larger than the resonant frequency of a passive EMI filter that features an attenuation comparable to that of a hybrid filter. In the important use case 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 description of the drawings]

[0022] [Figure 1] 1 illustrates a schematic diagram 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. [Diagram 3] 1 shows a differential transformer according to one embodiment. [Figure 4] 1 shows a differential transformer according to one embodiment. [Diagram 5] FIG. 11 is a control diagram of a current amplifier and / or a voltage amplifier according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] 1, an EMI filter 100 according to the 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 conductors L1, L2, L3 on the power supply line side and L1', L2', L3' on the load side. The load 300, which may be a motor drive with a cable and an electric motor, generates common mode noise and differential mode noise.

[0024] The power supply 5 may be any type of power supply arranged to supply power to the 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 the power supply 150. Power supply side means a location or electrical connection node on the power supply 150 closer to the power supply S than to the load L, while load side means a location or electrical connection node closer to the load L than to the 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 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 known, e.g. 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 towards the feeder, the filter 100 first has a load side passive stage 1. The passive filter 1 handles the highest level of noise with the largest bandwidth. The passive filter 1 attenuates the amplitude and reduces the bandwidth of the noise that is about to reach the 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 a configuration of capacitors, inductors and optional resistors that constitute a passive EMI filter stage 1. A passive filter does not depend on an external power source and a passive filter 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 especially the higher part of the frequency range. 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, 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 is reduced by passing through the passive filter 1 to a level that the active filter stages 2 and 3 can tolerate. This is mutually beneficial, since 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 it consists of a first inductive filter element 4 and a second inductive filter element 5 inductively coupled to a 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 mounted 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 comprises 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] The Y capacitors are well known and are generally connected to ground G. A network of X capacitors is called a delta connected capacitor network, whereas a network of Y capacitors is known as a star connected capacitor network. The delta connected capacitor network can be used to bypass differential mode noise, whereas the star connected capacitor network 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 supply 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 and it may in fact be embodied by any suitable DC source of low voltage, for example ±10V. 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 resonance may be damped by suitable 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 for suppressing 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 for suppressing 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 feedline side EMI filter stage 3 has the advantage that the feedline 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 with the lowest frequency and / or the highest amplitude. In the case of critical applications in which the load is a switching converter, the fundamental frequency may be the switching frequency, also called carrier frequency, of the converter in question.

[0042] The fundamental frequency may be a frequency 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 such 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. Because of this, ringing and oscillations in the EMI filter 100 are minimized, and resistors that are often installed to damp the oscillations can be omitted or designed to be small, significantly improving the performance of the filter 100. A high impedance can be achieved by selecting small values ​​of L and C in the passive elements 4, 5, 6, and the damping decreases at low frequencies. This is not a drawback, since the damping 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 with high frequencies as well.

[0044] In a further embodiment, the EMI filter 1 may be constructed 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 constructed without exhibiting a resonant phenomenon, since the resonances as a result of any stimulation are sufficiently damped or suppressed. The means combined with a special design for said resonant frequency make the EMI filter 1 work robustly and stably even in environments exhibiting high noise levels.

[0045] Adding the means for damping 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" for all intended applications. The damping means prevents any resonance phenomena in the EMI filter 1, even if the load-side passive EMI filter stage 1 is coupled to a noise-radiating load L that radiates noise with a fundamental frequency close to the resonant frequency of the load-side passive EMI filter stage 1. As a result, the load-side passive EMI filter stage 1 can be designed for a multitude of applications, albeit with 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 invention. The invention can also be applied to power generation systems or motors with regenerative braking. In the invention, the power supplied to the load L can be negative, instantaneous or continuous. In other words, the switching power converter can 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 a 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 cancellation current having the opposite sign to the noise current. The noise cancellation current is input to the feeder 150 to attenuate the common mode noise current circulating in this feeder. The variation shown is a feedback configuration. The cancellation current is input before the 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 supply line side active EMI filter stage 3 comprises a voltage amplifier circuit 11 whose input is connected to the supply 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 is 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 configured to suppress common mode noise, the feeder-side stage 3 is configured to suppress differential mode noise and acts on multiphase signals if the feeder 150 is a multiphase feeder. Since the common mode noise is handled by the intermediate stage, the feeder-side stage only handles 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 produces a cancellation voltage which is superimposed on the supply line voltage, thereby attenuating the noise. The filter of the invention is also shown in a feedback configuration, although for the intermediate stages, this is not required.

[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 a means for damping or suppressing oscillations, i.e. a capacitive discharge damping means 61 for damping or suppressing resonances. X1 ..C X3 One end of each of the capacitors C is connected to each of the phases 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 capacitive discharge damping means 61 including 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 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 A second circuit point 67 includes a second unidirectional conductor D2 and a second capacitor C Y2 The second unidirectional conductor D2 is disposed 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 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 allows current to flow in the forward direction better than in the reverse direction. Preferably, the unidirectional conductor allows current to flow almost completely in the forward direction and to block almost all current 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 form a first capacitor C Y1 receives only charges 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). Y1 and C Y2 The charge from the capacitor C cannot flow back to node 62. Y1 and C Y2 discharges across resistor R, reducing the time integral of that voltage and the common mode noise. Y1 and C Y2 ultimately reduces or prevents oscillations in the EMI filter 100, in particular in the load-side passive EMI filter stage 1, which may be stimulated by the noise radiation of the load device L with the fundamental frequency of this load device 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, 19b are made of a soft magnetic material with low coercivity and low hysteresis losses at frequencies where noise is expected, such as manganese zinc ferrite, nickel zinc ferrite, etc.

[0063] Each of the magnetic core elements 19a and 19b is provided with 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 is provided with three recesses corresponding to the three phases of the power supply line 150.

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

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

[0066] The first conductor 15a, the second conductor 15b and the third conductor 15c are disposed in respective recesses of the plurality of recesses. The 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 the power supply S and the load L or between the load L and the power supply S. Electrical insulation may be provided on each of the 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, 17c form the primary winding and magnetic core elements 19a, 19b form the magnetic core 19. These elements are part of a transformer, i.e., part of the differential transformer 10. The magnetic core element 19 may have an air gap 21 to linearize the inductance of the 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 those aspects of the differential transformer 10 in which a varying magnetic flux is generated in the magnetic core element 19 .

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

[0072] 4 shows a differential transformer 10, a power supply line 150 and an EMI filter for a three-phase AC system. Alternatively, the power supply line 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 the 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 with multiple 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 this power feeder 150. Therefore, top hat rail installation can be generally applied to the differential transformer 10.

[0074] 5 is a schematic diagram of an active filter stage as used in the intermediate stage 2 or mains 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 a 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 arranged to input a cancellation signal to a summing point B, which is located on the load side stage 300.

[0076] The active intermediate EMI filter stage 2 or the feed-line 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 of 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 predefined range, to the extent that the amplifier circuits 9, 11 are saturated. In normal conditions, when the noise level is below a predefined threshold, the second control loop LC2 is not activated and the gain K has its normal value.

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

[0079] When the load device L requires more power than defined during, for example, 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 damping means 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 the noise must be as wide 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 a suitable operating point for the loop gain, so that the slower speed of operation is beneficial.

[0082] This arrangement, having 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 EMI filter stages 2, 3, especially when the active intermediate EMI filter stage 2 and the feeder side active EMI filter stage 3 are arranged with the amplifier circuits 9, 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 the composition includes the steps of: - 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 conductors 15a, 15b, 15c between the first magnetic core element 19a and the second magnetic core element 19b; - The step of combining the first magnetic core element 19a and the second magnetic core element 19b is included.

[0085] By integrally combine, it is meant 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 remains between the first magnetic core element 19a and the second magnetic core element 19b. These magnetic core elements 19a, 19b are arranged such 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 ensuring the mutual position of the core elements 19a, 19b.

[0087] The method also includes a step of 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 feed line 150 and eases the associated manufacturing process.

[0091] Although the above embodiments or features describe different features 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 necessary, these embodiments or features may be implemented separately. [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 Grand 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. 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 power supply-side active EMI filter stage (3) connected to the power supply-side terminals (L1-L3) and configured to suppress differential mode noise.

2. 2. The EMI filter (100) of 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) of claim 1 or 2, wherein in association with a load device (L) that inputs noise having a fundamental frequency into 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. 4. The EMI filter (100) of 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) of claim 3 or 4, wherein the load device (L) includes a switching power converter, and the fundamental frequency of the noise is a carrier frequency of the switching power converter.

6. EMI filter (100) according to any one of claims 2 to 5, wherein the load-side passive EMI filter stage (1) comprises means configured to have a non-linear function for damping or suppressing oscillations.

7. 7. The EMI filter (100) of claim 6, wherein said 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. The EMI filter (100) of any one of claims 1 to 7, wherein the load-side passive EMI filter stage (1) comprises 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), each configured to suppress common mode noise, and further comprises 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. 3. The EMI filter of 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 canceling current into the power supply line (150).

10. The EMI filter (100) of 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) and configured to receive a noise voltage via a differential transformer (10) inductively coupled to the feeder (150) and to supply a noise canceling voltage to the feeder (150).

11. The EMI filter (100) of claim 10, wherein the noise canceling voltage includes a differential mode component and / or a common mode component.

12. The differential transformer (10) comprises: 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 said plurality of magnetic core elements; An EMI filter (100) according to claim 10 or 11, wherein said magnetic core elements (19a, 19b) are arranged to surround the conductors (15a-15c) of said feed line (150) to form a closed magnetic circuit.

13. 13. The EMI filter (100) of claim 12, wherein the power supply line (150) is a single-phase or three-phase or polyphase AC line, and the differential transformer (10) is configured as a single-phase or 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 intermediate active 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 ) and 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 a rectifier for the input signal (I) to avoid saturation in the amplifier circuit (9, 11). Ｓ ) in response to the first control loop (LC １ A gain control function (K) configured to adjust the gain function (K) of Ｃ The EMI filter (100) of any one of claims 2 to 13, comprising:

15. The second control loop (LC ２ ) of the gain control function (K Ｃ ) according to a linear function having an upper limit, １ 15. The EMI filter (100) of claim 14, wherein the gain function (K) of the filter (100) is adjusted.

16. The upper limit of the linear function is the gain control function (K Ｃ 16. The EMI filter (100) of claim 15, wherein the peak threshold target value (P) corresponds to a peak threshold target value (P) in the

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) of any one of claims 14 to 16, wherein the time constant is greater than the time constant of

18. A method for manufacturing an EMI filter (100) according to claim 10 or 11, comprising the steps of: - providing a plurality of electrical leads (15a-15c); - providing a first magnetic core element (19a) and a second magnetic core element (19b); - placing these conductors (15a-15c) between said first magnetic core element (19a) and said second magnetic core element (19b); - combining said first magnetic core element (19a) and said second magnetic core element (19b) to provide a closed magnetic path; - fixing said core elements (19a, 19b); - connecting said conductors (15a-15c) to load side terminals (L1'-L3') of the primary side of a differential transformer (10) and to supply side terminals (L1-L3) of the secondary side opposite to the primary side of said differential transformer (10).

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