Active common mode EMC filter

Abstract

The invention relates to an active interference filter in feedforward topology for active EMC filtering of interference signals which are coupled into a transmission line from an EMC source in an electronic circuit, comprising - a measuring device for detecting the interferences, - a high-pass filter unit, - a current injection unit, - a control unit, wherein - the current injection unit comprises a coupling capacitor connected to the transmission line and a voltage source, - the voltage source comprises an integrator circuit, - the integrator circuit comprises an operational amplifier and a feedback circuit connected between the output and the inverted input thereof, - the feedback circuit comprises a parallel connection of a first and second branch, wherein the first branch comprises a series circuit of a feedback capacitor and a compensation inductor.

Description

[0001] Description

[0002] ACTIVE EQUAL AC EMC FILTER

[0003] The present invention relates to a circuit arrangement in a feedforward structure for active EMC filtering of interference signals coupled from an EMC source into an electrical transmission line connected to the EMC source, wherein the circuit arrangement comprises a current measuring device, a high-pass filter unit, a current induction unit and a control unit.

[0004] Power electronics systems whose semiconductor switching elements are operated using pulse-width modulation (PWM) cause electromagnetic interference (EMI). Electromagnetic compatibility (EMC) refers to the ability of a technical device to avoid interfering with other devices through unwanted electrical or electromagnetic effects, or to be interfered with by other devices. To meet specified standards, such as EN 61800-3 for industrial applications, filters must generally be integrated into a power electronics system. These filters are classified as either passive or active.

[0005] Passive filters require a large volume, are heavy, and can cause resonances in conjunction with mains impedance. Active EMI filters (also known as "AEF" filters) do not have these disadvantages, provided they are properly controlled.

[0006] Numerous EMC filter structures are known, which can be divided into feedforward filters (FF structures) and feedback filters (FB structures). Generally, with a feedback structure, interference is detected where it is already suppressed by the active filter. One challenge of feedback structures is avoiding instabilities. With a feedforward structure, interference is measured where it is still unaffected by the active filter. Since there is no feedback loop to automatically adjust compensation to the level of interference, the challenge is typically to compensate for the interference as accurately as possible while avoiding errors due to modeling and nonlinearities.

[0007] A well-known active filter in a feedforward configuration is used to compensate for common-mode noise (CM) because it requires comparatively little power, while passive attenuation of CM is complex and requires considerable space. This active filter is built as a current-compensating topology, in which a voltage or current source is inserted between a coupling capacitor (for example, a Y-capacitor) and ground. The interference signal is generated via current sensing (CSCI, current sense, current injection).

[0008] The goal of the active filter is to generate a voltage that is exactly the inverse of the coupling capacitor's voltage for frequencies above the operating frequency (e.g., 50 Hz), thus resulting in a zero voltage at the coupling capacitor's connection point. The current in the Y-capacitor therefore represents the input signal, which, after conversion, leads to the compensation signal. Since the coupling capacitor ideally behaves like an integrator, this behavior can be replicated by an integrator, thereby achieving good AEF performance. It has been shown that the accuracy of an active filter constructed as described drops significantly at frequencies above approximately 100 kHz compared to the ideal (theoretical) behavior.

[0009] The object of the invention is to provide an active interference filter in a feedforward topology of the type described above for the active EMC filtering of interference signals, in which the attenuation of the interference signals is improved.

[0010] This problem is solved by a circuit arrangement having the features specified in claim 1.

[0011] The active interference filter according to the invention is designed as a feedforward topology for the active EMC filtering of interference signals that are coupled into a transmission line from an EMC source in an electronic circuit. The active interference filter comprises a measuring device for detecting the interference, a high-pass filter unit, and a current induction unit.

[0012] The current-injection unit includes a voltage source. This voltage source comprises an integrator circuit, which in turn includes an operational amplifier and a feedback circuit. The feedback circuit is conveniently connected between the output of the operational amplifier and its inverting input. The feedback circuit has a parallel connection of a first and second branch, with the first branch comprising a feedback capacitor and a compensation coil connected in series. The following equation can be derived to evaluate the performance of the active filter:

[0013] The intersection loss (IL) describes the current flowing through a mesh replica compared to the current flowing through the active filter. The smaller this value, the better the filter. For the derivation, it is assumed that the high-pass filter (GHP) and the current sensor (GCT) are ideal and have no influence on the performance of the active filter. It can then be determined that the filter's performance is exclusively proportional to 1 - Gint / Zc. Therefore, the integrator (Gint) must match the impedance of the injection capacitor as closely as possible.

[0014] The invention addresses the fact that the coupling capacitor, whose behavior is replicated by the integrator circuit (e.g., a y-capacitor), and parts of the other components exhibit parasitic inductance. As a result, the coupling capacitor no longer acts as an ideal integrator above a corner frequency determined by this parasitic inductance. Consequently, the accuracy of the active filter drops below its theoretical accuracy above this corner frequency. By incorporating the compensation coil as a series element with the feedback capacitor in the integrator circuit, the non-ideal behavior of the coupling capacitor is advantageously replicated. This significantly improves the accuracy of the active filter above 100 kHz.

[0015] Advantageous embodiments of the active interference filter according to the invention are described in the dependent claims. The embodiment of the independent claims can be combined with the features of one of the dependent claims or, preferably, with those of several dependent claims.

[0016] The dependent claims can be combined. Accordingly, the following additional features can be provided:

[0017] The measuring device for detecting disturbances can be designed as a current measuring device for the current in the transmission line. For example, the common-mode current can be measured by a filter coil present in a power converter for filtering differential-mode or common-mode disturbances. The specific implementation of the current measurement can also include a voltage measurement, for example, a voltage measurement across the coupling capacitor. The measurement can be performed using a Rogowski coil or a current transformer, or by an additional winding on an existing coil, such as a common-mode or common-mode filter choke.

[0018] The high-pass filter unit is conveniently connected between the current measuring device and the integrator circuit. In industrial networks, harmonics up to several kilohertz with significant amplitudes of up to several volts can occur. The active filter must be able to separate the interference from the network from the interference originating from the source being filtered. Otherwise, the active filter will work against the network, for which its performance is insufficient. To achieve sufficiently good separation, two methods are employed. Firstly, the topology used inherently provides separation of the interference, since only the current flowing between the converter and the y-capacitor is measured.

[0019] Preferably, the voltage generated in the integrator is buffered by a power stage connected downstream of the integrator, which can provide a sufficiently large current. The power stage can be implemented as an inverting or non-inverting circuit using an operational amplifier or from discrete components, e.g., as a push-pull stage.

[0020] In an advantageous embodiment, the compensation inductance has an inductance of no more than 150 nH. This advantageously avoids instability of the integrator.

[0021] This inductance corresponds to a parasitic inductance of approximately 15 nH with an input resistance Rmt of 10 ohms.

[0022] The second branch of the feedback circuit in the integrator circuit expediently includes either a feedback resistor or a feedback inductor. In both cases, this creates a high-pass filter. Using a parallel feedback inductor allows for an attenuation of -40 dB / dec. Conversely, using a feedback resistor results in an attenuation of -20 dB / dec.

[0023] A feedback resistor limits the amplitude of the integrator at low frequencies. Its value is preferably chosen such that the lower cutoff frequency fmt = 1 / (2 TT R L The Cmt value is at least 10 times lower than that of the high-pass filter unit. This ensures that the integrator does not dominate the behavior of the active filter at low frequencies and reduces the slope of the insertion loss to only -20 dB / decade.

[0024] Preferably, the high-pass filter unit is designed as a damped two-pole filter. For comparison, various topologies are considered. A second-order high-pass filter can be constructed as an undamped high-pass filter or as a damped high-pass filter. The damped high-pass filter can be implemented by a resistor R. C The frequency response of each filter is shown in Figure 1. A first-order filter (curve 11) and the damped second-order filter with Rc = 0 (curve 14) exhibit a cutoff frequency of -20 dB / dec, while the undamped second-order filter (curve 12) and the damped second-order filter with RL = 0 (curve 13) exhibit a cutoff frequency of -40 dB / dec.

[0025] To assess the discrimination between pass band and stop band, the formula introduced above for IL can be used, where Gint / Zc, GCT and GAMP are set to one.

[0026] For an active filter in a feedforward topology, however, not only the transfer function G of the high-pass filter itself is important, but also the transfer function (1 - G) should be considered. The transfer function (1 - G) describes the maximum performance that the active filter can achieve due to the high-pass filter, assuming otherwise ideal components. Figure 2 shows the curves 41 ... 44 of the transfer functions (1 - G) of the filters considered above.

[0027] It can be seen that a damped two-pole high-pass filter with a zero at 0 kHz and a zero at twice the pole (in the case shown, at 10 kHz) exhibits the best performance. There is a slight peak at the resonant frequency, followed by a 40 dB / decade roll-off. However, it is also evident that the filter characteristic can only roll off at a maximum of 40 dB / decade, so the lowest possible resonant frequency must be chosen to achieve the best possible attenuation of at least 40 dB at high frequencies.

[0028] It can be seen that the first-order filter (curve 21) and the second-order filter with R = 0 (curve 22) show a slope of only -20 dB / dec. The undamped second-order filter and the damped second-order filter with R c = 0 show a slope of -40dB / dec (curves 23, 24).

[0029] Therefore, the high-pass filter unit is preferably a second-order filter with R. c = 0. For example, in a simple configuration, it can be built from a filter capacitor and a series of damping resistors and filter coils. The terminals of the filter capacitor form the input and output terminals of the filter. The output terminal is further connected to the series of damping resistors and filter coils, the second terminal of which is connected to ground or a negative terminal of the signal lines.

[0030] This type of filter preferably includes a filter capacitor that is as ideal as possible (with the lowest possible parasitic resistance). The inductance of the filter coil must be high to achieve a cutoff frequency in the low kilohertz range. Such coils are quite large and often not suitable for high frequencies.

[0031] To counteract this, in a particularly advantageous embodiment and further development of the invention, the filter inductance is formed by a gyrator circuit. It was found that a gyrator circuit is much smaller and lighter than a coil with comparable inductance, while the limitation of the gyrator circuit to being suitable only for small signals is irrelevant in the active filter.

[0032] The proposed solution requires only an operational amplifier, two resistors, and a low-capacitance capacitor in surface-mount devices (SMD). This results in a very small installation space and thus offers a significant advantage over a comparable inductor.

[0033] Preferably, the high-pass filter unit comprises an operational amplifier whose output is coupled to its inverting input, and a series circuit consisting of a damping resistor and a gyrator capacitor is connected between the inverting and non-inverting inputs. The junction between the damping resistor and the gyrator capacitor forms a first terminal of the filter series circuit. A gyrator resistor is connected between the non-inverting input and a second terminal of the filter series circuit.

[0034] It is particularly advantageous to integrate two or more operational amplifiers, which are part of the active filter, into a single package. For example, the active filter can have an output amplifier with another operational amplifier that generates the input signal. Both operational amplifiers are combined in one package. Apart from that, the gyrator circuit then requires essentially only two SMD resistors and a capacitor, which require very little space.

[0035] Another aspect of the invention is an active interference filter in a feedforward topology for the active EMC filtering of interference signals coupled into a transmission line from an EMC source in an electronic circuit. This filter comprises a measuring device for detecting the interference, a high-pass filter unit, a current injection unit, and a control unit. The current injection unit includes a voltage source, and the high-pass filter unit is configured as a damped two-pole filter, in particular with a filter inductor. The filter inductor is preferably formed by a gyrator circuit.

[0036] In an alternative embodiment of the invention, the high-pass filter unit comprises a filter capacitor, a filter resistor, a low-pass filter and a subtraction circuit.

[0037] The gyrator circuit implements the following transfer function:

[0038] Where: d is the damping factor s n = s / CÜHP of the normalized complex frequency with CÜHP = 100 kHz s = jco the complex frequency. To achieve an even steeper transfer function above CÜHP, higher-order filters can be used. Advantageously, a fourth-order filter is implemented using the low-pass filter and the subtraction unit. This filter has the following transfer function:

[0039] (s„ + ds n + l) 2 — 1 G hp = (s 2 + ds n + l) 2

[0040] This transfer function can no longer be implemented with a known operational amplifier circuit. For its implementation, a filter capacitor is conveniently placed in the signal path, as this allows high voltages to be blocked. To represent an impedance Z x, which, together with the capacitor, yields the required transfer function, is based on a setup that is schematically shown in Figure 9.

[0041] The impedance Z is then x This is represented by a damping resistor Ri in series with a high-pass voltage source in conjunction with a drive circuit connected to the high-pass voltage source. The high-pass voltage source generates a high-pass signal from the input voltage v. in , which corresponds to the total voltage across the damping resistor and the high-pass voltage source, an output voltage v ou t. The transfer function of the control circuit is defined by G x designated.

[0042] The high-pass voltage source should provide a voltage v out = G x ■ v in generate.

[0043] The transfer function G is now being sought. x .

[0044] This results in

[0045] where the resonance frequency a) n = — — and thus s n = sR } can be chosen and thus RlCi

[0046] This function can be represented using a subtractor and an nth-order low-pass filter.

[0047] This design advantageously creates a high-pass filter unit that acts as a fourth-order filter, thus providing a very steep attenuation slope. With a high-pass filter unit featuring a cutoff frequency of 100 kHz, a slope of -80 dB / dec is achieved in the range between 100 kHz and 1 MHz, resulting in a much faster transition from the inactive to the active frequency range of the active filter. The attenuation curve is illustrated in Figure 3. Curves 31, 32, and 33 show the behavior without an active filter, with a single-pole high-pass filter, and with a two-pole high-pass filter. Curve 34 shows the improved behavior with a four-pole filter.

[0048] The subtraction circuit can include an operational amplifier, wherein the output of the operational amplifier is connected to the filter resistor, the low-pass filter is connected between a first input of the operational amplifier and the filter capacitor, and the second input of the operational amplifier is connected to the filter capacitor.

[0049] The low-pass filter can, for example, comprise two Sallen-Key filters. To increase the input impedance of the filter thus created, an impedance converter can advantageously be connected upstream of the low-pass filter. The impedance converter is arranged between the filter capacitor and the nodes of the low-pass filter and the subtraction circuit connected to it. A further aspect of the invention is therefore an active interference filter in a feedforward topology for the active EMC filtering of interference signals coupled into a transmission line from an EMC source in an electronic circuit, comprising a measuring device for detecting the interference, a high-pass filter unit, a current induction unit, and a control unit.The current input unit comprises a voltage source, the high-pass filter unit comprising a filter capacitor, a filter resistor, a low-pass filter and a subtraction circuit, the subtraction circuit in particular comprising an operational amplifier, wherein the output of the operational amplifier is connected to the filter resistor, the low-pass filter is connected between a first input of the operational amplifier and the filter capacitor and the second input of the operational amplifier is connected to the filter capacitor.

[0050] Preferably, the interference filter comprises an amplifier circuit downstream of the integrator circuit, with an operational amplifier and a third resistor connected to one of the inputs of the operational amplifier, wherein a third capacitor is connected in parallel to the third resistor.

[0051] Depending on where the active filter is used, several milliamperes to a few amperes are required to compensate for the interference. Operational amplifiers capable of driving these currents have a limited bandwidth. This bandwidth regulates the output amplitude to the input voltage. The transfer function of standard circuits is nearly constant up to the cutoff frequency.

[0052] However, it was recognized that the phase drops off at significantly lower frequencies due to the characteristics of the operational amplifier. This poses no problem in typical circuits, as only the amplitude of the circuit is optimized. In the case of feedforward topologies, however, a phase shift means that the compensation signal deviates in phase from the noise signal, and thus the noise is only inadequately compensated.

[0053] The addition of a third capacitor in parallel with the third resistor advantageously raises the output phase at higher frequencies. This counteracts the phase falloff of the operational amplifier up to a certain frequency. The third capacitor is conveniently chosen such that the cutoff frequency f = 1 / (2TTRC) of an input filter consisting of the third resistor and the third capacitor essentially corresponds to the cutoff frequency of the operational amplifier.

[0054] Another aspect of the invention is an active interference filter in a feedforward topology for the active EMC filtering of interference signals coupled into a transmission line from an EMC source in an electronic circuit. This filter comprises a measuring device for detecting the interference, a high-pass filter unit, a current induction unit, and a control unit. The current induction unit includes a voltage source. The interference filter includes an amplifier circuit downstream of the integrator circuit, comprising an operational amplifier and a third resistor connected to one of the inputs of the operational amplifier, with a third capacitor connected in parallel to the third resistor.

[0055] Advantageous applications of the active filter include, for example, power supplies. In industrial automation technology (e.g., in discrete manufacturing or process engineering) or in building automation, electronic power supplies are widely used to supply electrical loads, such as controllers, sensors, pumps, valves, etc., with electrical energy from a power grid.

[0056] The loads are supplied with a suitable, often predefined, voltage from the power supply. Typically, a high input voltage level from a single-phase or three-phase supply network, such as 230V AC, is converted to a lower and usually constant voltage level (e.g., 24V or 48V DC as the nominal output voltage) on the output side of the power supply.

[0057] Such power supplies are typically designed as switched-mode power supplies or switching power supplies (sometimes also referred to as switching power supplies). They usually have a housing and can be mounted on a DIN rail.

[0058] Such a switched-mode power supply typically comprises an input stage, for example in the form of a rectifier unit, a DC link, and a switching converter, which converts the AC voltage from the mains supply into a DC voltage for powering the load. The power supply then converts the usually unregulated input voltage into a constant output voltage for the electrical load, whereby a constant output voltage and / or output current is achieved by regulating the energy flow.

[0059] The power supply typically includes a passive filter. This passive filter is located between the input stage and the mains connections. It comprises one or more connecting branches from the input voltage terminals, each with a capacitor, to ground. The previously described active filter is part of the power supply. The active filter is preferably connected to a ground terminal of the passive filter's capacitors. These capacitors thus form the coupling capacitor.

[0060] Another type of power supply is used, for example, to control motors in industrial environments. The inverters used for this purpose typically also include an input stage in the form of a rectifier unit, a DC link, and a switching converter to generate the output voltage. Both the input and output voltages are typically three-phase. The inverter advantageously incorporates a passive filter, which is, for example, designed as an LCL filter. The LCL filter advantageously includes a y-capacitor. The active filter is preferably connected to one terminal of the y-capacitor. In this case, the y-capacitor acts as the coupling capacitor.

[0061] The invention will now be described and explained in more detail with reference to the exemplary embodiments shown in the figures. The figures, including those already mentioned in the text, show:

[0062] Figure 1 Transfer functions G of various high-pass filters,

[0063] Figure 2 Transfer functions 1 - G of the high-pass filter,

[0064] Figure 3 Transfer function 1 - G of high-pass filters compared to the fourth-order high-pass filter,

[0065] Figure 4 shows the construction of an active filter with a high-pass filter unit and an output amplifier circuit; Figure 5 shows the construction of an AC / AC converter with an active filter.

[0066] Figure 6 shows a single-phase AC / DC power supply with the active filter,

[0067] Figure 7 shows a high-pass filter unit with a gyrator circuit,

[0068] Figure 8: Impedance curves of inductors and a transfer function,

[0069] Figure 9 shows a schematic diagram of a fourth-order high-pass filter.

[0070] Figure 10 shows a fourth-order high-pass filter unit,

[0071] Figure 11 shows an output amplifier circuit.

[0072] Figure 4 shows the structure of an active filter 100 according to an embodiment of the invention. The active filter 100 comprises several units electrically connected in series with one another.

[0073] A first unit in a current measuring device 110 for determining the current in a connected electrical circuit.

[0074] A high-pass filter unit 120 is connected downstream of the current measuring device 110. The high-pass filter unit 120 is shown in Figure 4 as a series capacitor 121 and a series of a resistor 122 and an inductor 123 to ground, but it can also be constructed differently in other embodiments of the active filter 100.

[0075] An amplifier circuit 115 is connected between the current measuring device 110 and the high-pass filter unit 120. It serves to electrically decouple the current measuring device 110 and the high-pass filter unit 120. It comprises an operational amplifier 116 and two resistors 117, 118.

[0076] A high-pass filter unit 120 is followed by an integrator circuit 130. A voltage follower 125 is located between the high-pass filter unit 120 and the integrator circuit 130, serving to decouple the two surrounding units. The integrator circuit 130 is based on an operational amplifier 131. Its inverting input is coupled to the voltage follower 125 via an input resistor 132, while the non-inverting input is connected to ground. The integrator circuit 130 also includes a feedback circuit 133 connected between the output of the operational amplifier 131 and its inverting input. The feedback circuit has a parallel connection of a first and second branch, the first branch comprising a feedback capacitor 134 and a compensation coil 135 connected in series. The second branch comprises a series connection of a feedback coil 136 and a feedback resistor 137.The feedback coil 136 may not be present in other embodiments.

[0077] By incorporating the compensation coil 135 as a series element with the feedback capacitor 134 into the integrator circuit 130, the non-ideal behavior of the coupling capacitor is advantageously replicated. This significantly improves the accuracy of the active filter above 100 kHz.

[0078] A coupling amplifier 140 is connected downstream of the integrator circuit 130. The coupling amplifier 140 comprises an operational amplifier 141, whose inverting input is coupled to the integrator circuit 130 via an input resistor 142. A feedback resistor 143 is connected between the inverting input of the operational amplifier 141 and its output. Its non-inverting input is connected to ground. The output of the operational amplifier 141 forms the output of the active filter 100.

[0079] Figure 5 shows the construction of an AC / AC converter 200 with an active filter 270 according to an embodiment of the invention. The AC / AC converter 200 is connected to a three-phase power supply network 210. Following the connection to the power supply network 210, the AC / AC converter 200 includes a passive filter 220. The passive filter 220 comprises an LCL circuit with coupled filter coils 222 connected in series in the transmission lines 205 for filtering common-mode interference and coupled filter coils 224 connected in series in the transmission lines 205 for filtering differential-mode interference. A filter capacitor 223 is connected at a junction in the transmission lines 205 between the filter coils 222 and 224. The second terminals of the capacitors 226 are connected to each other and to ground via another filter capacitor 228. The transmission lines 205 are also connected to a rectifier 230.In the present embodiment, the rectifier 230 comprises three half-bridges connected in parallel with their outer terminals, each half-bridge having two series power semiconductor switches. The transmission lines 205 are connected to the center terminals of the half-bridges.

[0080] The external terminals of the half-bridges form a DC link with a DC link capacitor 240. An inverter circuit 250 is also connected to this, which in this example is constructed analogously to the rectifier 230. The output terminals of the inverter circuit are connected to a load, in this example an electric motor 260.

[0081] The AC / AC converter 200 also includes a control unit for the power semiconductor switches of rectifier 230 and inverter circuit 250, which is not shown in Figure 5.

[0082] The active filter 270 is connected to the AC / AC converter 200 in the area of ​​the passive filter 220. The current measuring device 110 is inserted into the transmission lines 205 and thus measures the total current in the transmission lines in a section between the coils 224 and the connection point for the capacitors 226. In other embodiments, the measurement can also be taken between the coils 224 and the rectifier. The output of the coupling amplifier 140 is connected between the capacitor 228 and ground.

[0083] Figure 6 shows the construction of a single-phase AC / DC power supply 300 with an active filter 370 according to an embodiment of the invention. The power supply 300 is designed as a switched-mode power supply or as a switching power supply unit (switched-mode power supply). It can, for example, be designed to be mounted on a DIN rail to enable easy installation in control cabinets.

[0084] A switched-mode power supply typically comprises a power stage and a control unit (hereinafter referred to as the "controller") for controlling the power stage. The power stage essentially consists of a converter, of which various types exist, such as flyback converters, forward converters, push-pull converters, boost converters, buck converters, etc. Depending on the current waveform present on the input and output sides, further distinctions are made, for example, between DC-DC converters, AC-DC converters, and DC-AC converters.

[0085] In the embodiment shown in Figure e, it is assumed that a DC load 310 is to be supplied from a supply network 320 in the form of an AC network. The power supply 300 is therefore supplied on the input side single-phase from the supply network 320 with an input voltage that is formed, for example, by a voltage difference between a phase conductor L and the neutral conductor N of the supply network 320. In principle, however, a three-phase supply from a three-phase supply network 210 is also possible. The power supply 300 comprises a rectifier unit 330, an intermediate circuit 340, and a switching transformer 350.

[0086] The input voltage, which can be, for example, a 230V AC voltage, is converted via the rectifier unit 330 as the input stage into a rectified DC link voltage at an output side of the rectifier unit 330, i.e., at an input side of the DC link 340. The DC link 340 can, for example, include a DC link capacitor 345. Further components can be connected to the DC link 340, such as additional capacitors to improve EMC performance.

[0087] The switching converter 350 is arranged on one output side of the intermediate circuit 340 and has at least one periodically operating electronic switching element. It can be designed, for example, as a potential-isolated switching converter, which has galvanic isolation (e.g., a transformer), or as a potential-bound (i.e., non-potential-isolated) switching converter 350 without galvanic isolation. For example, the switching converter 350 can be implemented as a DC / DC converter according to the LLC principle.

[0088] By regulating the energy flow through the power supply 300 with the help of a controller, the mostly unstabilized input voltage is converted into a regulated output voltage, for example a DC voltage of 28 V or 48 V to supply the load 310.

[0089] On the input side, a passive filter 360 can be provided between the rectifier unit 330 and the connection to the supply network 320. In this example, the passive filter 360 comprises two branches 361 and 362. Each of the branches 361 and 362 comprises two capacitors 363, one of which is connected to the live conductor L and the other to the neutral conductor N. The second terminal of each capacitor 363 is connected to ground. Two coupled coils 364 are connected between the two branches 361 and 362 in the live conductor and neutral conductor L and N.

[0090] In this example, the active filter 370 can be connected such that it simulates the common-mode voltage across the capacitors in both branches 361 and 362. For this purpose, the current measuring device 110 is installed near the connection point so that it measures the combined current of conductors L and N. The output of the coupling amplifier 140 is connected to ground.

[0091] Figure 7 shows an exemplary embodiment of a high-pass filter unit 700 for the active filter 100, 270, 370. This embodiment comprises a sub-circuit which is of the type of a gyrator circuit. It comprises an operational amplifier 710 and a damping resistor R. D , an auxiliary capacitor C Gy and an auxiliary resistor R Gy This sub-circuit replaces the series consisting of coil 122 and damping resistor 123. The high-pass filter capacitor 121 also remains part of the high-pass filter unit 120. The inductance of the sub-circuit is L Gy = RoRG y C Gy It can thus be achieved by choosing the elements, where RD « Rc y The requirement to maintain a high inductance must be met, while the size is minimal compared to a corresponding coil, as the elements used can be, for example, small SMD components.

[0092] Figure 8 shows a comparison of the impedances of an ideal coil (curve 81) with the impedance of the gyrator circuit (curve 82). It can be seen that up to a frequency of approximately 1 MHz, the impedance of the gyrator circuit follows the impedance of an ideal coil with an internal resistance. Only after this frequency, when the gain of the operational amplifier 710 decreases, does the impedance drop again. The effect of this non-ideality on the transfer function is shown by curve 83 in Figure 8. It can be seen that curve 83 exhibits a slope of -40 dB / dec until a value of -120 dB is reached at a frequency of approximately 1 MHz. Curve 83 remains at this value. For the actual active filter, this is not a significant limitation, as more dominant effects prevent the behavior from exceeding -60 dB.

[0093] Figure 10 shows another exemplary embodiment of a high-pass filter unit 1000 for the active filter 100, 270, 370. This embodiment implements a fourth-order filter. The cutoff frequency in this embodiment was chosen to be 100 kHz and the Butterworth filter coefficients were used.

[0094] The high-pass filter unit 1000 comprises a filter capacitor 1010 as its input element. Its second terminal forms the first node 1020 of the high-pass filter unit 1000. Connected to the first node 1020 is a voltage follower 1030, acting as an impedance converter, whose output forms a second node 1040. The second node 1040 also serves as the output of the high-pass filter unit 1000. The voltage follower 1030 is used here because the input impedance of the active filter is low at 12.1 kΩ. A further advantage of the voltage follower is that it provides a low-impedance output for the filter structure.

[0095] A low-pass filter circuit 1050 is connected to the second node 1040. The low-pass filter circuit 1050 comprises two Sallen-Key filter structures 1100 and 1200 connected in series. These are analogous, each containing an operational amplifier 1110 or 1210. The inverting input of each operational amplifier is connected to an input resistor 1140 or 1240 via a capacitor 1130 or 1230. The non-inverting input is connected to ground via a capacitor 1150 or 1250 and also to the input resistor via a resistor 1160 or 1260. The output of the low-pass filter circuit 1050 corresponds to the output of the second Sallen-Key filter structure 1200.

[0096] Furthermore, the high-pass filter unit 1000 includes a subtractor circuit 1060. The subtractor circuit 1060 includes an operational amplifier 1061. The non-inverting input of the operational amplifier 1061 is connected to ground via a resistor 1062 and to the second node 1040 via another resistor 1063. The inverting input of the operational amplifier 1061 is connected to its output via a resistor 1064 and to the output of the low-pass circuit 1050 via another resistor 1065. Finally, the output of the operational amplifier 1061 is connected to the first node 1020 via a resistor 1070.

[0097] The component values ​​used in this example are: Filter capacitor 1010: 1 pF; Resistors 1062... 1065: 100 kOhm; Resistor 1070: 5 Ohm; Capacitors 1130, 1230: 121 pF and 715 pF; Input resistors 1140, 1240: 12.1 kOhm and 4.75 kOhm; Capacitors 1150, 1250: 100 pF

[0098] Resistors 1160, 1260: 17.4 kOhm and 7.5 kOhm

[0099] Figure 11 shows an exemplary embodiment of the coupling amplifier 140. As already described in connection with Figure 4, the coupling amplifier 140 comprises the operational amplifier 141, the input resistor 142, and the feedback resistor 143. In the advantageous embodiment according to Figure 11, an input capacitor 144 is connected in parallel to the input resistor 142.

[0100] In another embodiment, the coupling amplifier 140 can also be implemented as a non-inverting amplifier circuit. As is generally known, in this case the input resistor 142 is connected between the inverting input of the operational amplifier 141 and ground. Here too, the input capacitor 144 is connected in parallel with the input resistor 142, i.e., between the inverting input of the operational amplifier 141 and ground.

[0101] The capacitance of the input capacitor 144 is chosen such that the cutoff frequency f = 1 / (2TTRC) of an input filter consisting of input resistor 142 and input capacitor 144 essentially corresponds to the cutoff frequency of the operational amplifier. If this is 294 MHz in an example, then with a value of 1.2 kΩ for the third resistor, only 4.5 pF is required for the input capacitor 144 for the best possible compensation.

[0102] Reference sign

[0103] 11 ... 14 Course of the transfer function G

[0104] 21...24 Course of the transfer function 1 - G

[0105] 31...34 Impedance curve of various inductors

[0106] Z x Impedance

[0107] Ri damping resistance vin input voltage v O output voltage

[0108] G x Transfer function of the control circuit

[0109] 100 active filters

[0110] 110 Current measuring device

[0111] 115 Amplifier circuit

[0112] 120, 700, 1000 high-pass filter unit

[0113] 121 High-pass filter capacitor

[0114] 122 Damping resistance

[0115] 123 coil

[0116] 125 Voltage followers

[0117] 130 Integrator circuit

[0118] 131 Operational amplifiers

[0119] 132 Input resistance

[0120] 133 Feedback circuit

[0121] 134 Feedback capacitor

[0122] 135 Compensation coil

[0123] 136 Feedback coil

[0124] 137 Feedback resistor

[0125] 140 coupling amplifiers

[0126] 141 Operational amplifiers

[0127] 142 Input resistance

[0128] 143 Feedback resistor

[0129] 200 AC / AC inverters

[0130] 205 transmission lines

[0131] 210 three-phase supply network

[0132] 220 passive filter

[0133] 222 coupled filter coils for filtering common-mode interference

[0134] 224 coupled filter coils for filtering differential-mode interference 226 filter capacitor

[0135] 228 Filter capacitor

[0136] 230 rectifiers

[0137] 240 Intermediate circuit capacitor

[0138] 250 Inverter Circuit

[0139] 260 electric motor

[0140] 270 Active Filter

[0141] 300 Power supply

[0142] 310 DC load

[0143] 320 single-phase supply network

[0144] L external conductor

[0145] N Neutral conductor

[0146] 330 rectifier unit

[0147] 340 Intermediate circle

[0148] 345 Intermediate circuit capacitor

[0149] 350 switching converters

[0150] 360 passive filter

[0151] 361, 362 branch

[0152] 363 Capacitor

[0153] 364 coupled filter coils

[0154] 370 active filters

[0155] 710 operational amplifiers

[0156] RD damping resistance

[0157] Cssy auxiliary capacitor

[0158] Rßy auxiliary resistor

[0159] 1010 Filter capacitor

[0160] 1020 first junction

[0161] 1030 Voltage Follower

[0162] 1040 second junction

[0163] 1050 low-pass circuit

[0164] 1060 subtractor circuit

[0165] 1061 operational amplifiers

[0166] 1062... 1065 resistors

[0167] 1070 resistor

[0168] 1100, 1200 Sallen-Key filter structures

[0169] 1110, 1210 Operation amplifier 1130, 1230 Capacitor

[0170] 1140, 1240 Input resistance

[0171] 1150, 1250 Capacitor

[0172] 1160, 1260 resistor

Claims

Patent claims 1. Active interference filter (100, 270, 370) in feedforward topology for active EMC filtering of interference signals coupled from an EMC source in an electronic circuit (200, 300) into a transmission line (205, L, N), comprising - a measuring device (110) for detecting the disturbances, - a high-pass filter unit (120, 700, 1000), - a current imprinting unit, wherein - the current imprinting unit includes a voltage source, - the voltage source includes an integrator circuit (130), - the integrator circuit (130) comprises an operational amplifier (131) and a feedback circuit (133), - the feedback circuit (133) comprises a parallel connection of a first and second branch, wherein the first branch comprises a series connection of a feedback capacitor (134) and a compensation inductor (135).

2. Active interference filter (100, 270, 370) according to claim 1, wherein the compensation inductance (135) has an inductance of no more than 150 nH.

3. Active interference filter (100, 270, 370) according to claim 1, wherein the second branch comprises a feedback resistor (137) or a feedback inductor (136).

4. Active interference filter (100, 270, 370) according to claim 1 with a damped two-pole filter as a high-pass filter unit (120, 700, 1000).

5. Active interference filter (100, 270, 370) according to claim 1, wherein the damped two-pole filter comprises a filter capacitor and a filter series connection of a filter inductor to a damping resistor, wherein the terminals of the filter capacitor serve as signal terminals of the high-pass filter unit (120, 700, 1000).

6. Active interference filter (100, 270, 370) according to claim 1, wherein the filter inductance is formed by a gyrator circuit.

7. Active interference filter (100, 270, 370) according to claim 6, wherein the filter series circuit comprises an operational amplifier (710), wherein - whose output is coupled to its inverting input, - a series circuit consisting of the damping resistor (R) between the inverting and non-inverting inputs D ) and a gyrator capacitor (Ce y ) is switched on, - the junction between the damping resistance (R D ) and the gyrator capacitor (Ccy) forms a first connection of the filter series circuit, - a gyrator resistor (R Gy ) is connected between the non-inverting input and a second terminal of the filter series circuit.

8. Active interference filter (100, 270, 370) according to one of claims 1 to 3, wherein the high-pass filter unit (120, 700, 1000) comprises a filter capacitor (1010), a filter resistor, a low-pass filter (1050) and a subtraction circuit (1060).

9. Active interference filter (100, 270, 370) according to claim 8, wherein the subtraction circuit (1060) comprises an operational amplifier (1061), wherein - the output of the operational amplifier (1061) is connected to the filter resistor, - the low-pass filter (1050) is connected between a first input of the operational amplifier (1061) and the filter capacitor (1010), - the second input of the operational amplifier (1061) is connected to the filter capacitor (1010).

10. Active interference filter (100, 270, 370) according to claim 8 or 9, wherein the low-pass filter (1050) comprises a series of two Sallen-Key filters (1100, 1200).

11. Active interference filter (100, 270, 370) according to one of claims 8 to 10 with an impedance converter (1030) between the filter capacitor (1010) and the nodes of the low-pass filter (1050) and the subtraction circuit (1060) connected thereto.

12. Active interference filter (100, 270, 370) according to one of the preceding claims with an amplifier circuit (140) downstream of the integrator circuit (130) comprising an operational amplifier (141) and a third resistor (142) connected to one of the inputs of the operational amplifier, wherein a third capacitor (143) is connected in parallel to the third resistor (142).

13. Active interference filter (100, 270, 370) according to claim 12, wherein the third capacitor (143) is selected such that the corner frequency of an input filter consisting of a third capacitor (143) is determined by the third capacitor. The resistance (142) and third capacitor (143) essentially correspond to the corner frequency of the operational amplifier (141).

14. Single-phase power converter (300), in particular switching power supply, for supplying a load from a supply network (320), comprising an active interference filter (100, 270, 370) according to one of the preceding claims.

15. Multiphase power converter (200), in particular three-phase AC / AC converter (200), for supplying a load (260) from a supply network (210), comprising an active interference filter (100, 270, 370) according to one of claims 1 to 13.

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