Active filter circuit for a power electronics circuit and system having an active filter circuit

Abstract

The invention relates to an active filter circuit (21a) for a power electronics circuit (23) and to a system having the active filter circuit, the active filter circuit (21a) comprising two input-end DC voltage terminals for connection of a DC voltage source (1), two output-end DC voltage terminals for connection of the power electronics circuit (23), two connecting lines (Tp, Tn) between the input-end and output-end DC voltage terminals, at least one measurement circuit (215), which is connected to the two connecting lines (Tp, Tn), at least one power supply unit (220) having two voltage input terminals (T+, T-), which are connected to the two connecting lines (Tp, Tn), and two voltage output terminals (VCC, T-), one of which is conductively connected to one of the two connecting lines (Tp, Tn) at the voltage input (T+, T-) of the power supply unit (220); and at least one amplifier (U1a) having two supply voltage terminals (VCC, VEE), which are connected to the at least one voltage output terminal (VCC, T-) of the power supply unit (220) and to the two connecting lines (Tp, Tn), a first input (Amp_in), which is connected to the measurement circuit (215), a second input, which is connected to a reference potential (ref) of the power supply unit (220), and an output, which can be connected to an electrical earth connection of the power electronics circuit (23) via a first capacitor (C4).

Description

[0001] Description

[0002] title

[0003] Active filter circuit for a power electronics circuit and system with an active filter circuit

[0004] The present invention relates to an active filter circuit for a power electronics circuit and a system with an active filter circuit.

[0005] Background of the invention

[0006] The operation of power electronic components in an electric vehicle generates significant interference signals that must be counteracted with appropriate EMC filters to ensure compliance with electromagnetic compatibility (EMC). Passive filters, active filters, or a combination of both can be used for this purpose. Active filters can utilize various types of signal coupling and input / output, which can result in different circuit configurations. For example, an interference signal can be extracted from the useful signal as an interference voltage, inverted, and then re-coupled into the useful signal as an interference suppression current. This method can utilize operational amplifiers, which typically use an electrical ground of the power electronic component to be suppressed as a reference potential. In this case, the operational amplifier must be powered by a separate power supply.This can either be connected to the electric vehicle's 12V electrical system or be implemented as an isolated DC / DC converter and connected to the electric vehicle's high-voltage electrical system. In the case of a power supply from the 12V electrical system, this results in increased wiring complexity, which requires additional filters to shield the wiring. In the case of an isolated DC / DC converter, this results in a high insulation complexity, which results in large and expensive components. Disclosure of the invention.

[0007] According to the invention, an active filter circuit for a power electronics circuit and a system with an active filter circuit are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0008] The invention represents a topological change of the active filter and its supply voltage circuit, which makes it possible to dispense with the connection to the 12V vehicle electrical system (and thus a potential bypass of the pre-filter) or the isolated DC / DC converter.

[0009] For this purpose, the invention makes use of the measure of relating the voltage supply of the active filter circuit to the DC voltage source of the system, ie the ground is no longer an external (e.g. housing) ground, but a potential of the DC voltage source, which in an electric vehicle can also be a high-voltage source (ie greater than 60 V).

[0010] The active filter circuit according to the invention comprises two input-side DC voltage terminals for connecting a DC voltage source, two output-side DC voltage terminals for connecting a power electronics circuit and two connecting lines between the input and output-side DC voltage terminals.

[0011] The active filter circuit also includes at least one measuring circuit connected to the two connecting lines. According to one embodiment, the measuring circuit may include a high-pass filter for coupling out an interference signal from the two connecting lines, which high-pass filter comprises a resistor (first resistor) and a capacitor (second capacitor).

[0012] The active filter circuit also includes at least one amplifier with a first and a second input and an output. The first input of the amplifier is connected to the measuring circuit, and the second input is connected to a reference potential of a power supply, which is also included in the active filter circuit. The active filter circuit can include more than one power supply. The amplifier has two supply voltage terminals for applying a supply voltage, which can be provided by the power supply. The amplifier can be a linear amplifier, which can, for example, include at least one operational amplifier. Other amplifier types are also possible.

[0013] The power supply contains two voltage input terminals and two voltage output terminals, with each of the two voltage input terminals connected to one of the two connecting lines, and one of the two voltage output terminals conductively connected to one of the two connecting lines on one of the power supply's two voltage input terminals. The two voltage output terminals of the power supply are connected to the amplifier's two supply voltage terminals. The amplifier's supply voltage terminals can also be connected to the two connecting lines via a capacitor each. The amplifier's output can be connected to an electrical ground of the power electronics circuit via a capacitor (first capacitor).

[0014] By conductively connecting one of the two voltage output terminals of the power supply to one of the two connecting lines, the DC voltage source and the power supply can have a common reference potential, which can correspond to either a potential on the first or second connecting line. The reference potential provided at the second input of the amplifier can be the common reference potential of the power supply and the DC voltage source, or a potential referenced to it. The power supply can be a buck converter, for example. Other non-isolated voltage converters are also possible.

[0015] At the first input of the amplifier, which is connected to the measuring circuit, an interference signal extracted from the circuit by the high-pass filter may be present. In particular, the first input of the amplifier may be an inverting input. The applied interference signal may result in a differential voltage between the two inputs of the amplifier, which can be compensated by the amplifier by subtracting the interference signal, which is identical in magnitude, via its connection to the connecting lines and injecting it into the electrical ground of the power electronics as an interference compensation signal. In this way, the interference signal in the connecting lines can be eliminated or at least reduced.

[0016] The described wiring of the active filter, in particular the reference of the amplifier's input signal to a potential of the DC voltage source instead of the electrical ground of the power electronics circuit, enables the use of a non-isolated voltage converter to provide the supply voltage for the amplifier, thus avoiding additional cabling and insulation effort.

[0017] The filter circuit is particularly suitable for preventing common-mode interference caused by rapid switching operations in the power electronics circuit. Common-mode currents flowing in the connecting lines between the DC voltage source and the power electronics circuit couple to an electrical ground of the power electronics circuit via the stray capacitance of the connecting lines. Using the active filter circuit presented here, this common-mode interference can be compensated or at least reduced.

[0018] The system according to the invention comprises the DC voltage source, a load, in particular in the form of an electric machine, at least one power electronics circuit and at least one active filter circuit according to the invention for the power electronics, which is described in more detail below. The power electronics circuit is arranged between the DC voltage source and the load and connected to the DC voltage source and the load. The active filter circuit is arranged between the DC voltage source and the power electronics circuit and connected in parallel to the power electronics circuit. In particular, the DC voltage source can be a high-voltage storage device. This can be used in particular as a traction battery in an electric vehicle and can be a DC voltage source when driving the vehicle and a DC voltage sink, e.g. during recuperation of kinetic energy of the vehicle or a charging process.The high-voltage storage device can have a voltage level of a few tens of volts to a few hundred volts. For example, modern traction batteries have nominal voltage levels of 400 to 800 volts.

[0019] Accordingly, the load can be an electrical machine that can operate as a motor and be supplied with electrical energy from the DC voltage source, or it can operate as a generator and supply electrical energy to the DC voltage source. The electrical machine can also be used in an electric vehicle. When the vehicle is powered by the electrical machine, it represents an AC voltage sink, whereas during recuperation of the vehicle's kinetic energy, it acts as a generator and represents an AC voltage source.

[0020] The power electronics circuit can, for example, be a power converter (so-called inverter), which converts the direct current supplied by the high-voltage storage device into the alternating current required to drive the electric machine. For this purpose, it can be operated, in particular, as an inverter. The power converter can also be operated as a rectifier to convert the alternating current supplied by the electric machine into direct current for feeding back into the direct current source. The power electronics circuit can also be a DC / DC converter or an on-board charger of an electric vehicle.

[0021] The claimed system is not limited to application in an electric vehicle, but can be used in any technical application (e.g., also in industrial applications such as machine tools, etc.). According to one embodiment, the system can further comprise at least one passive filter circuit, which can be arranged between the DC voltage source and the active filter circuit. Alternatively, the passive filter circuit can be arranged between the active filter circuit and the power electronics circuit, or two passive filter circuits can be included in the system, one of which can be arranged upstream and one downstream of the active filter circuit. The at least one passive filter circuit can have at least one inductive and / or at least one capacitive element.The at least one inductive element can be, for example, a common-mode choke, and the at least one capacitive element can be a capacitor. In particular, the at least one inductive and capacitive element can be combined.

[0022] According to one embodiment, the resistor of the high-pass filter of the measuring circuit (first resistor) can be connected to the two connecting lines, and the capacitor of the high-pass filter of the measuring circuit (second capacitor) can be connected to the electrical ground of the power electronics circuit. This arrangement results in particular from the interconnection of the amplifier, which is referenced to a potential of the DC voltage source instead of the electrical ground of the power electronics circuit and instead feeds the interference compensation signal into the connecting lines via the electrical ground of the power electronics circuit.

[0023] According to one embodiment, a third capacitor can be arranged between the first resistor and a first of the two connecting lines, and a fourth capacitor can be arranged between the first resistor and a second of the two connecting lines, wherein the two capacitors can have the same capacitance. This makes it possible to ensure that the high-pass filter of the measuring circuit is connected symmetrically to the two connecting lines. In particular, a capacitance value of the third and fourth capacitors can be higher than that of the second capacitor in the high-pass filter in order to prevent the high-pass filter from being influenced by the third and fourth capacitors. Analogous to the connection of the high-pass filter, according to a further embodiment, the amplifier can also be connected symmetrically to the connecting lines.In particular, a fifth capacitor can be arranged between the first connecting line and a first supply voltage terminal of the amplifier, and a sixth capacitor, which has the same capacitance value as the fifth capacitor, can be arranged between the second connecting line and a second supply voltage terminal of the amplifier. Due to the identical capacitance values ​​of the two capacitors, the amplifier is connected symmetrically to the two connecting lines, thereby preventing mode conversions, in particular a conversion from common-mode interference to differential-mode interference and vice versa.

[0024] In this context, according to a further embodiment, a seventh capacitor can be arranged between the first supply voltage terminal and the second supply voltage terminal of the amplifier, which capacitor is connected in series with the fifth and sixth capacitors and has a higher capacitance than these. The seventh capacitor can buffer voltages directly at the amplifier and counteract a voltage drop between the fifth and sixth capacitors.

[0025] In particular, the fifth and / or sixth capacitor can be designed as a Class X safety capacitor. If, for example, a positive potential of the DC voltage source is present on the first connecting line and a negative potential on the second connecting line and one of the two voltage output terminals of the power supply is conductively connected to the second connecting line, the DC voltage applied between the first and second connecting lines drops across the fifth capacitor, which is arranged between the first connecting line and the first supply voltage terminal of the amplifier, so that at least the fifth capacitor should be designed as a Class X safety capacitor.If, however, the relevant voltage output terminal of the power supply is conductively connected to the first connecting line, on which a positive potential of the DC voltage source is located, the DC voltage drops across the sixth capacitor, which is arranged between the second connecting line and the second supply voltage terminal of the amplifier, and at least the sixth capacitor should be designed as a Class X safety capacitor.

[0026] According to one embodiment, at least a second resistor can be connected in parallel to the third and / or fourth capacitor. In particular, a second resistor can be connected in parallel to the third capacitor and a further second resistor can be connected in parallel to the fourth capacitor. The resistors can be selected such that they form a voltage divider which provides a direct voltage at an output of the measuring circuit which corresponds to that at the first input of the amplifier. The latter depends in particular on the reference potential of the power supply which is applied to the second input of the amplifier. By means of the voltage divider, a potential difference between the output of the measuring circuit and the first input of the amplifier is avoided, whereby a capacitor can be dispensed with at this point or it can have a low dielectric strength.

[0027] Alternatively or in addition to the voltage divider, an eighth capacitor can be arranged between the output of the measuring circuit and the first input of the amplifier. If the voltage divider described above is omitted, the eighth capacitor can be a Class X safety capacitor, in particular, to withstand potentially high DC voltages. In combination with the voltage divider, a conventional capacitor without an X classification, which has a low dielectric strength, can be used.

[0028] According to one embodiment, a low-pass filter can be arranged between the two voltage output terminals of the power supply and the two supply voltage terminals of the amplifier. This allows them to be decoupled from the potential of the connecting line connected to one of the two voltage output terminals of the power supply in the relevant frequency range of the interference signal, and a symmetrical connection of the amplifier to the connecting lines can be ensured. According to one embodiment, the reference potential of the power supply can be a center voltage of the voltage applied between the two voltage output terminals, i.e., an interference signal at the input of the amplifier can be related to the center voltage of the power supply, which can be provided at a reference voltage output terminal. This can be particularly advantageous if the amplifier is an operational amplifier or if the amplifier comprises operational amplifiers.

[0029] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0030] The invention is illustrated schematically in the drawings using an embodiment and is described below with reference to the drawings.

[0031] Short description of the drawings

[0032] Figure 1 shows schematically a system with a DC power source, a load, a power electronics circuit and an active filter circuit not according to the invention.

[0033] Figure 2 shows schematically a system according to an embodiment of the invention with a DC power source, a load, a power electronics circuit and one active and two passive filter circuits.

[0034] Embodiment(s) of the invention

[0035] Figure 1 schematically shows a system 200 with a direct current source 1 (not described in more detail), a load 3 (not described in more detail), a power electronics circuit 23 (not described in more detail), and an active filter circuit 21 not according to the invention. The active filter circuit 21 and the power electronics circuit 23 are arranged between the direct current source 1 and the load 3, and the filter circuit 21 is connected in parallel to the power electronics circuit 23. The direct current source 1 has two direct voltage connections T+, T-, to each of which a positive connecting line (high-voltage line) Tp and a negative connecting line Tn are connected, which connect the power electronics 23 to the direct current source 1. The power electronics 23 in the present case contains three alternating voltage connections U, V, W, to which the load 3 is connected.

[0036] The active filter circuit 21, not according to the invention, contains two first capacitors C03, C04, each of which forms a high-pass filter with a resistor R1 to decouple an interference signal from the positive connecting line Tp or the negative connecting line Tn, which may occur, for example, due to rapid switching operations in the power electronics circuit 3. For this purpose, the resistor R1 is connected in series with the first capacitors C03, C04 to an electrical ground of the power electronics circuit. Furthermore, the active filter 21, not according to the invention, comprises a voltage amplifier U1 and two second capacitors C01, C02. The voltage amplifier U1 has an inverting input and a non-inverting input "+", the latter being connected to the electrical ground of the power electronics circuit.

[0037] The interference voltage extracted by the high-pass filter O3, R1 or O4, R1 is applied to the inverting input of the voltage amplifier U1, amplified appropriately, and fed back into the connecting lines Tp, Tn via the second capacitors O1, O2. In this way, an interference signal on one of the connecting lines Tp, Tn can be eliminated or at least reduced by coupling in a compensation signal that is inverse to the interference signal.

[0038] However, due to the connection of the non-inverting input "+" of the amplifier U1 to the electrical ground of the power electronics circuit, a separate power supply 220 is required, which must, for example, provide a positive voltage VCC and a negative voltage VEE.

[0039] If the active filter circuit 21 shown is used in an electric vehicle, the required power supply 220 can either be connected to its 12V electrical system or be designed as an isolated DC / DC converter and connected to the high-voltage electrical system of the electric vehicle. This results in increased cabling effort in the case of a power supply from the 12V electrical system, which requires additional filters to shield the cabling, and in the case of an isolated DC / DC converter, a high insulation effort, which results in large and expensive components.

[0040] Figure 2 schematically shows a system 200 according to an embodiment of the invention with a DC power source 1, a load 3, a power electronics circuit 23 and an active filter circuit 21a according to an embodiment of the invention and two passive filter circuits 22a, 22b.

[0041] The direct current source 1 can, for example, be a high-voltage storage device, in particular a traction battery 1, for an electric vehicle, and the load 3 can be an electric machine 3 of the electric vehicle (not shown). The power electronics circuit 23 can, for example, be a power converter (so-called inverter) which, for example, converts the direct voltage supplied by the traction battery 1 into an alternating voltage required to drive the electric machine 3. For this purpose, it can be operated, in particular, as an inverter. It can also be provided that the power converter can be operated as a rectifier in order to convert the alternating voltage supplied by the electric machine into direct voltage for feeding back into the direct voltage source. The power electronics circuit 23 can also be a DC / DC converter or an on-board charger of an electric vehicle.

[0042] Analogous to the system shown in Figure 1, the active filter circuit 21a and the power electronics circuit 23 are arranged between the direct current source 1 and the load 3, and the filter circuit 21a is connected in parallel to the power electronics circuit 23. Here, too, the direct current source 1 has two direct voltage terminals T+, T-, to each of which a positive connecting line (high-voltage line) Tp and a negative connecting line Tn are connected, which connect the power electronics 23 to the direct current source 1. The power electronics 23 contains three alternating voltage terminals U, V, W, to which the load 3 is connected. In the present case, two passive filter circuits 22a, 22b (not described in detail) are additionally arranged upstream and downstream of the active filter circuit 21a.These can be configured to suppress remaining interference signals, for example, those in a frequency range that the active filter circuit 21a cannot cover. For this purpose, the two passive filter circuits 22a, 22b can contain, for example, inductive elements and capacitive elements. The inductive elements can be, for example, common-mode chokes, and the capacitive elements can be capacitors.

[0043] The shown active filter circuit 21a according to an embodiment of the invention includes a measuring circuit 215, an amplifier U1a, a power supply 220 and a low-pass filter 221.

[0044] By means of the measuring circuit 215, which is connected to the two connecting lines Tp, Tn, an interference signal Inoise (indicated by the black arrows) coupled via the electrical ground of the power electronics circuit 23 can be extracted from the positive or negative connecting line Tp, Tn and fed to a first input AMPJn of the amplifier U1a. In particular, the first input AMPJn can be an inverting input of the amplifier.

[0045] An unspecified second input of amplifier U1a is connected to a reference potential of power supply 220 (indicated by the designation "ref" at this input), and an unspecified output of amplifier U1a is connected via a first capacitor C4 to an electrical ground of power electronics circuit 23. Furthermore, two supply voltage terminals VCC, VEE of amplifier U1a are connected both to power supply 220 and, via capacitors C7, C8, to the two connecting lines Tp, Tn.

[0046] The measured interference signal applied to the first input AMPJn of amplifier U1a can result in a differential voltage between the two inputs of amplifier U1a, which can be compensated by the amplifier by injecting an interference compensation signal linj (indicated by the white arrows) into the electrical ground of power electronics 23. As a result, a resulting interference signal Ires (indicated by the hatched arrows) in the connecting lines Tp, Tn can become zero or at least very small.

[0047] A capacitor C7 (fifth capacitor) is arranged between a first supply voltage terminal VCC and the positive connecting line Vp, and a capacitor C8 (sixth capacitor) is arranged between a second supply voltage terminal VCC and the positive connecting line Vp. These two capacitors C7 and C8 can, in particular, have the same capacitance value so that the amplifier U1a is connected symmetrically to the connecting lines Tp and Tn. This is particularly necessary to reduce common-mode interference and avoid mode conversion from common-mode to differential-mode interference.

[0048] A capacitor C6 (seventh capacitor) is also arranged between the first supply voltage terminal VCC and the second supply voltage terminal VEE of amplifier U1a, and is connected in series with capacitors C7 and C8. This capacitor can, in particular, have a higher capacitance than capacitors C7 and C8 to counteract a voltage drop between them. Furthermore, in this case, at least capacitor C7 can be a Class X safety capacitor, since the DC voltage (i.e., possibly high voltage) between the connecting lines is dropped across it.

[0049] The power supply 220 is connected on the input side to the two connecting lines Tp and Tn and has two voltage outputs VCC and T-. The voltage output terminal T- is conductively connected to the negative connecting line Tn and thus has the same potential as it. The two voltage outputs VCC and T- are referenced to the reference potential "ref" of the power supply 220, which in this case corresponds to the center voltage (UT- ± Uvcc / 2). It is also possible to connect one of the two voltage outputs VCC and T- of the power supply 220 to the positive connecting line Vp. In this case, the reference potential "ref" of the power supply 220 changes to (UT+ ± Uvcc / 2), and the DC voltage between the connecting lines drops across capacitor C8, which should then be a Class X safety capacitor.

[0050] The low-pass filter 221, which is not described in detail, is arranged between the power supply 220 and the two supply voltage terminals VCC, VEE of the amplifier U1a, which serves to decouple the supply voltage terminals VCC, VEE of the amplifier U1a from the potential of the negative connecting line Tn in order to in turn bring about a symmetrical connection of the amplifier U1a to the connecting lines Tp, Tn.

[0051] The measuring circuit 215 comprises a high-pass filter with a capacitor C3 (second capacitor) and a resistor R1 (first resistor), wherein the resistor R1 is connected to the two connecting lines Tp, Tn, and the capacitor C3 is connected to the electrical ground of the power electronics circuit 23. For symmetrical connection of the high-pass filter to the connecting lines Tp, Tn, a capacitor C2 (third capacitor) is arranged between the resistor R1 and the positive connecting line Tp, and a capacitor C1 (fourth capacitor) is arranged between the resistor R1 and the negative connecting line Tn. Furthermore, a voltage divider R3, R4 (second resistor) is connected in parallel to the capacitors C2, C1. This ensures that a potential at the output CM_sense of the measuring circuit is at the same level as the potential at the first input AMPJn of the amplifier U1a.In this way, a capacitor C5 (eighth capacitor) can have a small dielectric strength and does not have to be a Class X safety capacitor.

Claims

Claims 1. An active filter circuit (21a) for a power electronics circuit (23), the filter circuit comprising two input-side DC voltage terminals (T+, T-) for connecting a DC voltage source (1); two output-side DC voltage terminals for connecting the power electronics circuit (23); two connecting lines (Tp, Tn) between the input and output-side DC voltage terminals; at least one measuring circuit (215) connected to the two connecting lines (Tp, Tn); at least one power supply unit (220) with two voltage input terminals (T+, T-), wherein one of the two voltage input terminals (T+, T-) is connected to one of the two connecting lines (Tp, Tn), and two voltage output terminals (VCC, T-), one of which is conductively connected to one of the two connecting lines (Tp, Tn) at the voltage input (T+, T-) of the power supply unit 220;and at least one amplifier (U1a) with two supply voltage terminals (VCC, VEE) connected to the two voltage output terminals (VCC, T-) of the power supply (220), a first input (Ampjn) connected to the measuring circuit (215), a second input connected to a reference potential (ref) of the power supply (220) and an output connectable to an electrical ground of the power electronics circuit (23) via a first capacitor (C4); 2. Active filter circuit (21a) according to claim 1, wherein the measuring circuit (215) contains a high-pass filter (R1, C3) for coupling out an interference signal from the two connecting lines (Tp, Tn), which comprises a first resistor (R1) and a second capacitor (C3), wherein the first Resistor (R1) is connected to the two connecting lines (Tp, Tn), and the first capacitor (C3) is connectable to the electrical ground of the power electronics circuit (23).

3. Active filter circuit (21a) according to claim 2, wherein a third capacitor (C2) is arranged between the first resistor and a first of the two connecting lines (Tp), and a fourth capacitor (C1) is arranged between the first resistor (R1) and a second of the two connecting lines (Tn), which fourth capacitor has the same capacitance value as the third capacitor (C2).

4. Active filter circuit (21a) according to claim 3, wherein the third and fourth capacitors (C2, C1) have a higher capacitance value than the second capacitor (C3).

5. Active filter circuit (21a) according to one of the preceding claims, wherein a fifth capacitor (C7) is arranged between the first connecting line (Tp) and a first supply voltage terminal (VCC) of the amplifier (U1a), and a sixth capacitor (C8) is arranged between the second connecting line (Tp) and a second supply voltage terminal (VEE) of the amplifier (U1a), which has the same capacitance value as the fifth capacitor (C7).

6. Active filter circuit (21a) according to claim 5, wherein a seventh capacitor (C6) is arranged between the first supply voltage terminal (VCC) and the second supply voltage terminal (VEE) of the amplifier (U1a), which is connected in series with the fifth capacitor (C7) and the sixth capacitor (C8) and has a higher capacitance value than these.

7. Active filter circuit (21a) according to one of claims 3 to 6, wherein at least one second resistor (R2, R3) is connected in parallel to the third and / or fourth capacitor (C2, C1).

8. Active filter circuit (21a) according to one of claims 3 to 7, wherein an eighth capacitor (C5) is arranged between an output of the measuring circuit (CM_sense) and the first input (AMPJn) of the amplifier (U1a).

9. Active filter circuit (21a) according to one of the preceding claims, wherein a low-pass filter (221) is arranged between the two voltage output terminals (VCC, T-) of the power supply (220) and the two supply voltage terminals (VCC, VEE) of the amplifier (U1a).

10. Active filter circuit (21a) according to one of the preceding connections, wherein the reference potential (ref) of the power supply (220) is a center voltage of the voltage between the two voltage output terminals (VCC, T-).

11. A system (200) comprising a DC voltage source (1); a load (3); at least one power electronics circuit (23) arranged between the DC voltage source (1) and the load (3) and connected thereto; and at least one active filter circuit (21a) according to one of the preceding claims, arranged between the DC voltage source (1) and the power electronics (23) and connected in parallel thereto.

12. System (200) according to claim 11, further comprising at least one passive filter circuit (22a, 22b) arranged between the DC voltage source (1) and the active filter circuit (21a) and / or between the active filter circuit (21a) and the power electronics circuit (23).

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