WO2014040901A1

WO2014040901A1 - Method and device for producing a filter, and a filter

Info

Publication number: WO2014040901A1
Application number: PCT/EP2013/068352
Authority: WO
Inventors: Nicholas Demetris CHEROUVIM
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-09-13
Filing date: 2013-09-05
Publication date: 2014-03-20
Also published as: DE102012216266A1

Abstract

The invention relates to a method for producing a filter (10) for providing a particular reactive power for an AC/DC converter (20). The filter (10) comprises a coil (30) and a plurality N of capacitors (41, 42,..., 4N) which can be independently connected to the coil (30) in order to form N filter configurations. The method comprises the following steps, a) to c). In step a), in the filter configuration that has N capacitors (41, 42,..., 4N) connected to the coil (30), a resonance frequency of the filter (10) is adjusted (201) as a function of a particular harmonic oscillation of the AC/DC converter (20). In step b), a total capacitance of the filter (10) and an inductance (L) of the coil (30) are determined (202) as a function of the particular reactive power and the adjusted resonance frequency. In step c), the capacitances (C1, C2, CN) of the N capacitors (41, 42,..., 4N) are adapted (203) such that any resonance frequency of the N filter configurations lies outside a number of predetermined frequency windows around harmonic oscillations which are generated by the AC/DC converter (20), and the particular total capacitance remains constant. This adaptation of the capacitances (C1, C2, CN) of the capacitors (41, 42,..., 4N) of the filter (10) ensures that none of the possible resonance frequencies of the filter can coincide with a harmonic oscillation of the AC/DC converter (20). In addition, a computer program product and a device for producing a filter, as well as such a filter, are disclosed.

Description

description

Method and device for producing a filter and filter

The present invention relates to a method and an apparatus for producing a filter for providing a specific reactive power for an AC / DC converter. Furthermore, the present invention relates to such a filter for providing a specific reactive power for an AC / DC converter.

The filter may in particular be a line filter or a line filter device for a power electronic device and comprise a circuit of filter capacitors and a filter choke. The filter capacitors are connected in this case to form a filter circuit, whereby harmonics or harmonic oscillations, that is to say frequency components above a mains fundamental frequency, are attenuated in voltage profiles of alternating voltages of the network phase conductors. This improves the electromagnetic compatibility (EMC) of the electronic device in the power supply network, via which the device is supplied with electrical energy. In particular power electronic devices in which fast switching operations (for example, a

Pulse width modulation) can cause voltage spikes in network phase conductors are often operated together with a line filter. A mains filter is often either directly connected to the power grid or separated from this only by a main protection, which then but also the device itself is disconnected from the power grid. Therefore, when such a device is coupled to the power grid, it flows in the filter capacitors of the line filter

Reactive currents. These can become large in relation to the total current consumption, in particular, when the device itself is not operated. If there are many devices over If the same line phase conductors are connected to the power supply network and only a few of these devices are operated simultaneously, the reactive currents of the line filters of the individual devices can add up to considerable total blind currents, which may even exceed the value of the total active power required by the devices at this time ,

These reactive currents cause heating of the mains phase conductors. In addition, a correspondingly high apparent power must be provided in the central energy supply, for example by inductive consumers or phase shifters. In addition to the problem of compensation or generation of reactive power, there is also the problem of harmonics or harmonic oscillations already discussed above.

Further, the use of a passive filter or input filter for the filter can cause problems if the resonant frequency of the filter itself is too close to the harmonic vibrations generated by the AC / DC converter. In this case, oscillations may occur in the system which can damage individual components.

Overall, active filters or passive filters can be used as the input filter for an AC / DC converter. Although active filters can achieve better filtering results than passive filters, they are more complex and expensive. In contrast, the advantage of using passive filters is mainly their low cost and simplicity. With passive filters, it is possible to turn certain filter capacitors on or off according to the operating point of the AC / DC converter. In this case, the reactive power can be compensated for a larger operating range. However, then there is the problem of the emergence of a transient when connecting or disconnecting the capacitors, which in turn can lead to impairment or damage to the components of the system. A conventional solution for compensating the reactive power at the input of an AC / DC converter is the use of banks of capacitors. Individual capacitors or bridges of capacitors may be switched on or off to provide more or less reactive power to the AC / DC converter. However, this does not solve the filtering of the harmonic generated by the AC / DC converter.

A circuit for connecting capacitors and for changing the frequency of the resulting filter is described in US Pat. No. 6,940,358 B1. Further, document CN101083397A shows designs for passive filters in which no components are switched on or off. US Pat. No. 7,656,117 B2 discloses a line filter device with a filter capacitor circuit which can be disconnected from the line phase conductors of a power supply network via controllable switching elements. The

Filter capacitor circuit is always switched to the mains phase conductor only when a converter for operating an electrical machine requires a real power from the power grid.

Further, document US 4,317,076 A shows a control system for automatically adding and subtracting capacitors from an electrical supply line to regulate a power factor of the electrical supply line.

It is an object of the present invention to provide an improved filter.

Accordingly, a method is proposed for producing a filter for providing a specific reactive power for an AC / DC converter. The filter has a coil and a plurality N of capacitors which are independently connectable to the coil to form N filter configurations. The method comprises the following steps a) to c). In step a), a resonant frequency of the filter is added the filter configuration with N of the coil switched capacitors in response to a specific harmonic oscillation of the AC / DC converter set. In step b), a total capacitance of the filter and an inductance of the coil are determined as a function of the determined reactive power and the set resonance frequency. In step c), the capacitances of the N capacitors are adjusted such that each resonant frequency of the N filter configurations is outside a number of predetermined frequency ranges around harmonic oscillations generated by the AC / DC converter and the determined total capacitance remains constant.

The present adaptation of the capacitances of the capacitors of the filter ensures that none of the possible resonance frequencies of the filter can coincide with a harmonic oscillation of the AC / DC converter. The use of the frequency window around the respective harmonic oscillation of the AC / DC converter provides a certain safety margin between the possible resonance frequencies of the AC / DC converter

Filters and the harmonic oscillations of the AC / DC converter ready. In particular, as the particular harmonic vibration to which the resonance frequency of the filter is set, the strongest harmonic vibration is used. Thus, the filter will optimally attenuate even the strongest harmonic oscillation of the AC / DC converter at the nominal operating point.

Another advantage of the filter according to the invention is the use of only simple and inexpensive components, namely a single coil and a number of N capacitors. For coupling the capacitors to the coil only corresponding switches are provided. In one embodiment, prior to step c), the capacitance of each of the N capacitors is set to an Nth part of the determined total capacitance. The adjustment of the capacitances of the N capacitors to the respective N part of the determined total capacitance of the filter constitutes a suitable initialization of the method for adjusting the capacitances.

In a further embodiment, step c) is formed by the following substeps c1) to c5):

cl) connecting the n-th capacitor to the coil to form an n-th filter configuration, with ne [1, ..., N], wherein the n-th filter configuration is formed by a number n capacitors connected by the coil .

c2) calculating the resonant frequency at the nth filter configuration,

c3) checking whether the calculated resonant frequency of the n-th filter configuration is outside the number of predetermined frequency windows,

c4) if the calculated resonant frequency of the nth filter configuration is outside the number of predetermined frequency windows, setting the capacitance of the nth capacitor to the Nth part of the determined total capacitance, and c5) if the calculated resonant frequency is the nth Filter configuration is within one of the predetermined frequency window, setting the capacitance of the n-th capacitor to a value which is larger by a certain amount than the Nth part of the determined total capacity, and setting the capacity of the (n + 1) th capacitor to a value that is smaller than the Nth part of the determined total capacity by the specified amount. This ensures that all possible resonant frequencies of the filter do not coincide with the harmonic oscillations of the AC / DC converter and that the specific total capacitance of the filter is maintained. Further, in step c5), it is possible to set the capacity of the nth capacitor to a value smaller than the Nth part of the specific total capacity by the predetermined amount, and then the capacitance of the (n + 1) th capacitor - is set to a value that is greater than the Nth part of the determined total capacity by the specified amount. In a further embodiment, sub-steps cl) to c5) are iteratively executed for the N filter configurations.

The iterative implementation of sub-steps cl) to c5) ensures that the total capacity of the filter remains constant and the individual capacities can be set appropriately.

In another embodiment, the resonant frequency in the nth filter configuration is calculated by:

where f _{n is} the resonant frequency of the n-th filter configuration, f _{N is} the resonant frequency of the N th filter configuration, n is the number of capacitors connected to the coil, and N is the number of capacitors switchable to the coil, with ne [1, ..., N].

In a further embodiment, the following condition is checked in step c3) as to whether the calculated resonant frequency f _{n is} outside the number of predetermined frequency windows:

(Elharm "fbase ^~ fwindow)>()"f> (^ lharm "fbase + fwindow) / n

where n _ha rm denotes the order of the harmonic oscillation generated by the AC / DC converter, fbase the fundamental frequency of a power supply network which can be coupled to the AC / DC converter, and fwindow the limit frequency of the predetermined frequency window.

In another embodiment, step c3) is performed for all harmonic oscillations of the AC / DC converter up to the 13th order. Preferably, therefore, only the harmonic oscillations of the AC / DC converter up to the 13th order are compensated, which represents a suitable compromise between the complexity of the method and the filter performance.

In a further embodiment, the AC / DC converter is designed as a six-pulse rectifier. The six-pulse rectifier may also be referred to as a three-phase rectifier.

In another embodiment, the coil is formed as a three-phase choke coil.

In another embodiment, step a) is formed by: setting the resonant frequency of the filter in the filter configuration with the N capacitors connected to the three-phase choke coil to the 5th harmonic of the six-pulse rectifier.

The fifth harmonic of the six-pulse rectifier represents the strongest harmonic for the six-pulse rectifier, thus providing the appropriate basis for adjusting the resonant frequency of the filter.

In another embodiment, N is selected depending on the nominal input voltage of the AC / DC converter, the nominal output voltage of the AC / DC converter, and a transient when connecting the capacitors.

Consequently, when designing the filter, the nominal input voltage, the nominal output voltage and switching operations can also be taken into account.

In another embodiment, step d) is formed by: adjusting the capacitances of the N capacitors so that each resonant frequency of the N filter configuration outside the number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter, and the determined total capacitance and inductance of the coil remain constant.

In this embodiment, in particular, the inductance of the coil is kept constant.

Furthermore, a computer program product is proposed, which causes the execution of the method as explained above on a program-controlled device.

A computer program product such as a computer program means, for example, as a storage medium, such as memory card, USB stick, CD-ROM, DVD or in the form of a

Downloadable file can be provided or delivered by a server in a network. This can be done, for example, in a wireless communication network by transmitting a corresponding file with the computer program product or the computer program means.

In addition, a data carrier with a stored computer program with commands is proposed, which causes the execution of the method explained above on a program-controlled device.

Furthermore, an apparatus for producing a filter for providing a specific reactive power for an AC / DC converter is proposed. In this case, the filter has a coil and a plurality N of capacitors, which can be connected to the coil independently to form N filter configurations. The device comprises an adjustment means, a determination means and an adaptation means. The adjusting means is arranged to set a resonance frequency of the filter in the filter configuration with N of the coil connected capacitors in response to a certain harmonic oscillation of the AC / DC converter. The determination means is for determining a total capacity of the filter and an inductance of the coil in dependence on the specific reactive power and the set resonance frequency. The matching means is arranged to adjust the capacitances of the N capacitors such that each resonant frequency of the N filter configurations is outside of a number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter and the particular total capacitance remains constant. The respective means, setting means, determination means and adaptation means, can be implemented in terms of hardware and / or software technology. In a hardware implementation, the respective means can be designed as a device or as part of a device, for example as a computer or as a microprocessor. In a software implementation, the respective means may be designed as a computer program product, as a function, as a routine, as part of a program code or as an executable object.

Furthermore, a filter is proposed for providing a specific reactive power for an AC / DC converter, which is produced in particular by a method as described above. In this case, the filter has a coil and a plurality N of capacitors for the formation of a specific total capacitance, which can be connected to the coil independently to form N filter configurations. The capacitances of the N capacitors are adjusted such that each resonant frequency of the N filter configurations is outside of a number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter and the particular total capacitance remains constant.

The above-described characteristics, features and advantages of this invention as well as the manner in which they are achieved will become clearer and more clearly understood in connection with the following description of the embodiments. Games, which are explained in more detail in connection with the drawings.

Showing:

Fig. 1 is a block diagram of an embodiment of a

Filter coupled to an AC / DC converter;

FIG. 2 is a flowchart of a first embodiment of a method for producing a filter for providing a specific reactive power for an AC / DC converter; FIG.

3 is a flowchart of a second embodiment of a method for producing a filter for providing a specific reactive power for an AC / DC converter; and

Fig. 4 is a block diagram of an embodiment of a

Device for producing a filter for providing a specific reactive power for an AC / DC converter.

In the figures, the same or functionally identical elements have been given the same reference numerals, unless stated otherwise.

FIG. 1 shows a block diagram of an exemplary embodiment of a filter 10 which is coupled to an AC / DC converter 20.

The AC / DC converter 20 receives on the input side an AC voltage from a connected power supply network 50, converts the received AC voltage into a DC voltage and provides this on the output side of a load 60. For this purpose, the AC / DC converter 20 is coupled to the power supply network 50 via three line phase conductors on the input side. The three mains phase conductors generate the alternating voltage from the energy supply network 50 to the AC / DC converter 20 transmitted. At these three network phase conductors and the filter 10 is coupled. On the output side, the AC / DC converter 20 is coupled to the load 60 via two lines for the transmission of the converted DC voltage.

The filter 10 of FIG. 1 is adapted to provide a certain reactive power for the AC / DC converter 20 and to couple this to the AC / DC converter via the three mains phase conductors on the input side. For this purpose, the filter 10 has a coil 30 and a plurality N of capacitors 41-4N for forming a specific total capacitance of the filter 10. The N capacitors 41-4N are independently connectable to the coil 30 to form N filter configurations. For independently and selectively connecting the capacitors 41-4N to the coil, intermediate switches 71-7N are provided. Depending on the individually coupling reactive power, the capacitors 41-4N of the coil 30 are switched on. For this purpose, the corresponding switches 71-7N are closed. For this purpose, the switches 71-7N are controlled by a control device (not shown). Further, the capacitances Cl-CN of the N capacitors 41-4N are adjusted such that each resonant frequency of the N filter configurations is outside of a number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter 20 and the certain total capacitance remains constant. Exemplary embodiments of methods for producing such a filter 10 are given with reference to FIGS. 2 and 3. 2 shows a flowchart of a first embodiment of a method for producing a filter 10 for providing a specific reactive power for an AC / DC converter 20. The filter 10 has a coil 30 and a plurality N of capacitors 41-4N (see FIG 1), the N capacitors 41-4N of the coil 30 for forming N filter configurations are independently switchable. The embodiment of FIG. 2 comprises the following steps 201 to 203.

In step 201, a resonance frequency of the filter 10 in the filter configuration, which is constituted by capacitors 41-4N connected by N of the coil 30, is set in response to a certain harmonic of the AC / DC converter. The AC / DC converter 20 is a six-pulse rectifier, for example, and the coil 30 is, for example, a three-phase reactor. Then, the resonant frequency of the filter 10 in the filter configuration with the N connected to the three-phase reactor 30 capacitors 41-4N can be set to the fifth harmonic of the six-pulse rectifier 20, since the fifth harmonic see vibration of the six-pulse rectifier 20 represents the strongest harmonic vibration , In this case, the number N is selected as a function of the nominal input voltage of the AC / DC converter 20, of the nominal output voltage of the AC / DC converter 20 and of a transient when connecting the capacitors 41-4N.

In step 202, a total capacitance of the filter 10 and an inductance L of the coil 30 are determined depending on the determined reactive power and the set resonance frequency.

In step 203, the capacitances Cl-CN of the N capacitors 41-4N are then adjusted such that each resonant frequency of the N filter configurations is outside of a number of predetermined frequency windows from the AC / DC converter

20 harmonic vibrations generated and the specific total capacity remains constant. In particular, the

Step 203 performed such that the specific inductance L of the coil 30 remains constant.

FIG. 3 shows a flow chart of a second exemplary embodiment of a method for producing a filter 10 for Provide a specific reactive power for an AC / DC converter 20.

The second embodiment of FIG. 3 comprises the following steps 301-307.

In step 301, a resonant frequency of the filter 10 is set in the filter configuration with N of the capacitors 41-4N connected to the coil 30 in response to a certain harmonic oscillation of the AC / DC converter 20.

In step 302, a total capacitance of the filter 10 and an inductance L of the coil 30 are determined in dependence on the determined reactive power and the set resonance frequency. At this time, to initialize the succeeding steps 303-307, the capacitance Cl-CN of each of the N capacitors 41-4N is set to an Nth part of the determined total capacity. Subsequent steps 303-307 are iterated for the N filter configurations.

In this case, in step 303, the nth capacitor 41-4N is connected to the coil 30 to form an nth filter configuration, with n e [1,..., N]. In this case, the nth filter configuration is formed by a number n of capacitors 41-4N connected by the coil 30.

In step 304, the resonant frequency is calculated at the nth filter configuration. In particular, the equation f _{N is} used. f _n denotes the resonance fre

frequency of the n-th filter configuration, f _N the resonant frequency of the N th filter configuration, n the number of capacitors connected to the coil, and N the number of capacitors which can be connected to the coil, with ne [1, ..., N]. In step 305, it is then checked whether the calculated resonant frequency of the n-th filter configuration is outside the number of predetermined frequency windows. At step 305, it is checked by the following condition whether the calculated resonance frequency f _{n is} outside the number of predetermined frequency windows:

(Π-harm "fbase ~ fwindow)> ()" f> (^ -harm "fbase + fwindow) /

n

where n _ha rm denotes the order of harmonic oscillation generated by the AC / DC converter, fbase denotes the fundamental frequency of a power supply network which can be coupled to the AC / DC converter, and f _w i _n dow denotes the cutoff frequency of the predetermined frequency window. If the calculated resonant frequency of the nth filter configuration is within one of the determined frequency windows, the method continues to step 307. Otherwise, step 306 occurs. In step 306, the capacitance Cl-CN of the nth capacitor 41-4N is set to the Nth part of the determined total capacitance. On the other hand, in step 307, the capacitance Cl-CN of the n-th capacitor 41-4N is set to a value larger than the N-th part of the specific total capacitance by a certain amount, the capacitance Cl-CN of the (n + 1) -th capacitor 41-4N is set to a value smaller than the Nth part of the determined total capacity by the predetermined amount. As a result, the determined total capacity is kept constant.

FIG. 4 shows a block diagram of an exemplary embodiment of a device 80 for producing a filter 10 for providing a specific reactive power for an AC / DC converter 20. An example of such a filter 10 with an AC / DC converter 20 coupled thereto is shown in FIG. The device 80 of FIG. 8 has an adjustment means 81, a determination means 82 and an adjustment means 83. The adjustment means 81 is arranged to set a resonance frequency of the filter 10 in the filter configuration with N of the coil 30 switched capacitors 41-4N depending on a particular harmonic oscillation of the AC / DC converter 20 set. The determination means 80 is configured to determine a total capacitance of the filter 10 and an inductance L of the coil 30 as a function of the determined reactive power and the set resonance frequency. The matching means 83 is arranged to adjust the capacitances C 1 -C n of the N capacitors 41-4N such that each resonant frequency of the N filter configurations is outside a number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter 20 and the specific total capacity remains constant.

Although the invention has been further illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

claims

A method of manufacturing a filter (10) for providing a specific reactive power to an AC / DC converter (20), the filter (10) comprising a coil (30) and a plurality N of capacitors (41, 42, .. ., 4N) which are independently connectable to the coil (30) to form N filter configurations, comprising the steps of:

a) setting (201) a resonant frequency of the filter (10) in the filter configuration with N of the coil (30) connected capacitors (41, 42, ..., 4N) in response to a specific harmonic oscillation of the AC / DC converter ( 20), b) determining (202) a total capacitance of the filter (10) and an inductance (L) of the coil (30) in dependence on the determined reactive power and the set resonance frequency, and

c) adjusting (203) the capacitances (C1, C2, CN) of the N capacitors (41, 42, ..., 4N) such that each resonant frequency of the N filter configurations is outside a number of predetermined frequency windows from the AC / DC converter (20) generated harmonic vibrations and the specific total capacity remains constant.

2. The method according to claim 1,

characterized,

that before step c) the capacitance (C1, C2, CN) of each of the N capacitors (41, 42, ..., 4N) is set to an Nth part of the determined total capacitance.

3. The method according to claim 2,

characterized,

that step c) comprises the following substeps c1) to c5):

cl) connecting (303) the nth capacitor (41, 42,

4N) to the coil (30) to form an nth filter configuration, with ne [1, N], the nth filter configuration being defined by a number n of capacitors (41, 42, ... , 4N) is formed, c2) calculating (304) the resonant frequency at the n-th filter configuration,

c3) checking (305) whether the calculated resonant frequency of the nth filter configuration is outside the number of predetermined frequency windows,

c4) if the calculated resonant frequency of the n-th filter configuration is outside the number of predetermined frequency windows, determining (306) the capacitance (Cl, C2,

CN) of the nth capacitor (41, 42, ..., 4N) to the Nth part of the determined total capacitance, and

c5) if the calculated resonant frequency of the nth filter configuration is within one of the predetermined frequency windows, setting (307) the capacitance (Cl, C2, CN) of the nth capacitor (41, 42, ..., 4N) to a value which is larger by a certain amount than the Nth part of the determined total capacity, and setting the capacitance (C1, C2, CN) of the (n + 1) th capacitor (41, 42,

4N) to a value less than the Nth part of the determined total capacity by the predetermined amount.

4. The method according to claim 3,

characterized,

the sub-steps cl) to c5) are carried out iteratively for the N filter configurations.

5. The method according to claim 3 or 4,

characterized,

that the resonance frequency in the n-th filter configuration is calculated by:

where f _{n is} the resonant frequency of the nth filter configuration, f _{N is} the resonant frequency of the Nth filter configuration, n is the number of capacitors (41, 42, ..., 4N) connected to the coil (30), and N is the number of Coil (30) switchable capacitors (41, 42, ..., 4N), with ne [1,

N].

6. The method according to claim 5,

characterized,

in step c3) it is checked by the following condition whether the calculated resonant frequency f _{n is} outside the number of predetermined frequency windows:

2 - 2

(Elharm "^ base ~ fwindow)>(^)" £ ^" N>(Elharm" fbase + fwindow) / where n _ha rm is the order of the harmonic oscillation generated by the AC / DC converter (20), fbase is the fundamental frequency of a with the AC / DC converter (20) coupled power supply network (50) and f _w indow the cutoff frequency of the predetermined frequency window called.

7. The method according to claim 6,

characterized,

that step c3) is performed for all harmonic oscillations of the AC / DC converter (20) up to the 13th order.

8. The method according to any one of claims 1 to 7,

characterized,

in that the AC / DC converter (20) is designed as a six-pulse rectifier.

9. The method according to claim 8,

characterized,

the coil (30) is designed as a three-phase choke coil.

10. The method according to claim 9,

characterized,

that step a) is formed by:

Setting the resonant frequency of the filter (10) in the filter configuration with the N capacitors (41, 42, ..., 4N) connected to the three-phase choke coil (30) to the 5th harmonic of the six-pulse rectifier (20).

11. The method according to any one of claims 1 to 10, characterized,

in that N depends on the nominal input voltage of the AC / DC converter (20), on the nominal output voltage of the AC / DC converter (20) and on a transient when connecting the capacitors (41, 42, ..., 4N) is selected.

12. The method according to any one of claims 1 to 11,

characterized,

that step c) is formed by:

Adjusting the capacitances (Cl, C2, CN) of the N capacitors (41, 42, ..., 4N) such that each resonant frequency of the N filter configurations is generated outside the number of predetermined frequency windows to be generated by the AC / DC converter (20) harmonic oscillations and the specific total capacitance and the specific inductance (L) of the coil (30) remains constant.

13. Computer program product, which causes the execution of a method according to one of claims 1 to 12 on a program-controlled device.

14. Apparatus (80) for producing a filter (10) for providing a specific reactive power for an AC / DC converter (20), wherein the filter (10) comprises a coil (30) and a plurality N of capacitors (41, 42 , ..., 4N) which are independently connectable to the coil (36) to form N filter configurations, comprising:

an adjusting means (81) for setting a resonant frequency of the filter (10) in the filter configuration with capacitors (41, 42,

4N) in response to a particular harmonic of the AC / DC converter (20),

a determination means (82) for determining a total capacitance of the filter (10) and an inductance (L) of the coil (30) in dependence on the determined reactive power and the set resonance frequency, and

matching means (83) for adjusting the capacitances (Cl, C2, CN) of the N capacitors (41, 42, ..., 4N) such that each resonant frequency of the N filter configurations is outside of a number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter (20) and the determined total capacitance remains constant.

15. A filter (10) for providing a specific reactive power for an AC / DC converter (20), in particular produced by a method according to one of claims 1 to 12, wherein the filter (10) comprises a coil (30) and a plurality N of capacitors (41, 42, 4N) for forming a specific total capacitance, which are independently connectable to the coil (30) to form N filter configurations, the capacitances (Cl, C2, CN) of the N capacitors (41, 42,. .., 4N) are adapted such that each resonant frequency of the N filter configurations is outside a number of predetermined frequency windows around harmonic oscillations generated by the AC / DC converter (20) and the determined total capacitance remains constant.