Inductive reactance apparatus

The invention relates to an inductive reactance apparatus for use with an energy converter comprising at least two convert er units operating in a parallel manner, wherein the induc tive reactance apparatus is configured to couple the at least two converter units with a power grid, both providing at least two phases of an alternating voltage, the inductive re actance apparatus comprising at least two first magnetic mem bers, wherein one of the first magnetic members is provided for each one of the at least two converter units, each of the first magnetic members has a number of first limbs corre sponding to the number of the phases, each of the first mag netic members has a first and a second yoke member, wherein first ends of the first limbs are connected to the first yoke member, and second ends of the first limbs are connected to the second yoke member, and each of the first limbs is pro vided with a respective first winding having a first end adapted to be connected with a respective one of the convert er units and a second end configured to be coupled with a re spective one of the phases of the power grid, wherein all these first windings have the same sense of winding. Moreo ver, the invention also relates to an energy converter for coupling an energy source connected to the energy converter with a power grid, both of the energy converter and the power grid providing at least two phases of an alternating voltage, the energy converter comprising at least two converter units, each of the converter units being configured to provide power conversion with regard to the at least two phases, a control device for controlling at least the converter units, wherein the control device is configured to operate the converter units in a parallel manner, and an inductive reactance appa ratus for connecting the converter units with the power grid.

Energy converters as well as inductive reactance apparatuses are well known in the art so that it appears not necessary to indicate specific related documents of the art. Generally, energy converters are used in the technical field of generat ing or distributing of electric power. Energy converters are suited to couple at least two energy distributing networks for example a DC-network with an AC-network, or the like. The DC-network may be provided by an energy source such as a bat tery device, a photovoltaic module, a wind generator and/or the like. It also may be provided by a generator supplying an alternating voltage that may have one/or more phases. The AC- network may be adapted to provide two or more phases of an alternating voltage. Therefore, the energy converter can be any of, for example, a DC/DC-converter for instance such as a booster, a buck, or the like, an AC/DC-converter, such as an inverter, an AC/AC converter such as a frequency converter, or the like.

Today, energy converters are usually formed as static energy converters id est, they - contrary to dynamic energy convert ers - do not have any moveable, especially rotatable, parts for the purpose of energy conversion. Static energy convert ers are usually formed as switched electric energy converters and include, for the purpose of energy conversion, at least one converter inductivity as well as at least one switching element which are connected with each other such that suita ble switching of the switching element provides the energy conversion. In the present case, each converter unit compris es at least one converter inductivity and at least one switching element.

A switching element in this disclosure preferably refers to a controllable electronic switching element, especially, a con trollable electronic semiconductor switch provided, for in stance, by a transistor operated in a switching mode, a thy ristor, combined circuitries with such semiconductor switch es, preferably with fly back diodes parallel connected to the semiconductor switch, a gate-turn-off-thyristor (GTO), an in- sulated-gate-bipolar-transistor (IGBT), combinations thereof, or the like. Basically, the switching element may also be formed by at least one field effect-transistor, especially, a metal-oxide-semiconductor-field effect transistor (MOSFET).

For the purpose of energy conversion, the at least one switching element is operated in a switching mode. With re gard to the semiconductor switch formed by a transistor, this requires that, in a switched-on status, between connections of the transistors forming a switchable path, a very low electric resistance is provided so that a high current flow is established at a very small residual voltage. In a turned- off status, the switching path of the transistor provides a high resistance so that, when the voltage at the switching path is very high, substantially no or only a very small, es pecially, neglectable current flow is allowed. Differing here from is a linear mode of transistors, which is usually not used in switched energy converters.

The energy converter therefore allows an electric coupling between the networks which the energy converter is connected with in order to provide an energy exchange between these networks. For instance, if the energy converter is connected to a DC-network, on one hand, and to an AC-network, on the other hand, the energy converter provides for a suited volt age adaptation so that the energy coupling can be realized. The energy converter is designed respectively.

The energy converter, especially its converter units, need not only have one single converter inductivity and/or one single switching element. Depending on the application, two or more switching elements and/or two or more converter in ductivities can be provided for each of the converter units in order to provide the required energy conversion.

Preferably, the switching elements are connected with a con trol device in order to control the switching operation of the switching elements with regard to their switched status. Preferably, the connection is formed such that each of the switching elements can be controlled individually. The control device can be provided by an electronic circuitry generating the respective control signals for the switching elements so that the desired switched mode of the respective switching element can be achieved. The electronic circuitry can have electronic components for generating the control signals. Moreover, the electronic circuitry can also comprise a computer for generating the control signals which is con trolled by a computer program. Especially, the control device can consist of the computer only. The control device may be a separate component with regard to the energy converter or its converter units. However, it is preferably integral with the energy converter, especially its converter units.

The control device is configured to control the switching el ements with regard to their switching status so that the en ergy converter, especially its converter units, provide the desired energy conversion function between the energy distri bution networks connected to the energy converter.

Moreover, the control device is preferably configured to con trol the power to be converted by the energy converter, espe cially the converter units. The control device may control the converted power individually for each of the converter units. In order to provide this control functionality, the control device may be connected with one or more respective sensor elements which allow determining, for instance, a re spective voltage, a respective current, a respective electric power, and/or the like. The at least one sensor element may be a separate component or it may be an integral component of the energy converter.

Especially, if the energy converter is configured to convert high electric power, the energy converter is usually composed of two or more converter units which are operated in a paral lel manner. This design has some technical advantages as it is possible to reduce electromagnetic interferences and to increase the efficiency especially with regard to a low power requirement.

Energy converters, which may be configured as frequency con verters or the like, are usually operated in the switching mode. The switching mode can be based on pulse wide modula tion (PWM) in order to allow energy conversion with a high degree of efficiency. Such switching modes are well known in the art. Two major methods for providing PWM are preferably used, namely, continuous pulse wide modulation (CPWM) and discontinuous pulse wide modulation (DPWM).

In order to provide reduction of interferences, especially interferences on conductors or lines, respectively, the ener gy converter usually comprises the inductive reactance appa ratus. The inductive reactance apparatus usually comprises an electronic circuitry composed of inductivities and capaci tors. Especially, it is well known to provide a LCL-filter with the inductive reactance apparatus. The inductive reac tance apparatus is suited to reduce distortion and/or inter ferences caused by the switching elements of the converter units during the determined operation of energy conversion. The distortion may comprise one or more of the switching fre quencies and harmonics caused by the converter units.

In order to reduce or eliminate electric interferences, espe cially with regard to the conductors of the respective energy distribution networks, the energy converter may comprise usu ally the inductive reactance apparatus. The inductive reac tance apparatus comprises plural electric components and may be a heavy apparatus. As the switching frequency of the ener gy converter, especially its converter units, is usually much higher than a frequency of the voltage of the network, espe cially the alternating voltage, the inductive reactance appa ratus serves to reduce interferences caused by this opera tion. Also, the operation of the energy converter causes a respec tive high-frequency ripple on the desired alternating voltage which is supposed to be reduced by the inductive reactance apparatus. Filtering components such as the before-mentioned inductivities or chokes, respectively, are required. These components are usually heavy components and expensive.

A respective inductive reactance apparatus is already dis closed by US 2017/0229937 A1 related to a choke for inter leaved switching. Although this teaching has been considered by those skilled in the art, further improvement is desired. Especially, this teaching fails to consider common mode in terferences .

Therefore, it is the object of the invention, to improve an inductive reactance apparatus as well as an energy converter such that the size and the costs of such a component can be reduced and/or the efficiency of reduction of interferences can be improved.

As a solution, the invention proposes an inductive reactance apparatus as well as an energy converter according to the in dependent claims.

Preferable embodiments can be derived from the features ac cording to the dependent claims.

According to a first aspect for a generic inductive reactance apparatus, it is proposed that the inductive reactance appa ratus comprises a second magnetic member having a number of second limbs corresponding to the number of the phases and a third and a fourth yoke member, wherein first ends of the second limbs are connected to the third yoke member and sec ond ends of the second limbs are connected to the fourth yoke member, wherein each of the second limbs is provided with at least one second winding having a first end being connected with at least one of the respective first windings and a sec ond end configured to be connected with a respective one of the phases of the power grid, in order to couple the at least one of the respective first windings with a respective one of the phases of the power grid, and wherein the yoke members are arranged such that the first yoke members are connected with the third yoke member and the second yoke members are connected with the fourth yoke member.

With regard to a second aspect for the generic inductive re actance apparatus, it is proposed that the inductive reac tance apparatus comprises a second magnetic member having a third and a fourth yoke member, wherein the yoke members are arranged such that the first yoke members are connected with the third yoke member and the second yoke members are con nected with the fourth yoke member, and the third and/or the fourth yoke member comprises a common mode suppression wind ing.

With regard to the energy converter it is proposed that the inductive reactance apparatus is designed according to the first or the second aspect of the invention.

The invention is based on the idea that interferences, espe cially on the lines or conductors, respectively, can be dif ferential mode interferences and/or common mode interfer ences. Generation of such interferences is limited by, for instance, law, standard, and/or the like. Such operating con ditions, also referred to as electromagnetic compatibility (EMC), are the ability of electric equipment and systems to be operated in its electromagnetic environment, by limiting undesired generation, propagation and reception of electro magnetic energy which may cause unwanted effects such as electromagnetic interference (EMI), or even physical damage in an operating equipment. The target of EMC is a correct, undisturbed operation of different equipment in a common electromagnetic environment. Consequently, the inductive re actance apparatus is directed to reduce emission of electro magnetic energy which is generated by the operation of the converter units. A certain standard, dealing with EMC, is, for example, EN 61000. However, further standards can be rel evant for a specific applications, so e.g. EN 50121 for track-bound vehicles and devices, or the like.

In this regard, the inductive reactance apparatus of the in vention is preferably directed to reduce both, the differen tial mode interferences as well as the common mode interfer ences. This improves also the teaching of US 2017/0229937 A1 which does not deal with the different kinds of interfer ences, and which's teaching appears to consider not common mode interferences. Therefore, it is a thought of the inven tion to integrate a common mode reduction property into an inductive reactance apparatus such as known from the US 2017/0229937 A1. So, the size of the inductive reactance apparatus and its costs can be reduced.

According to the invention, the before-mentioned thought can be realized by the second magnetic member which is addition ally provided to the first magnetic members. Preferably, for each converter unit, a respective first magnetic member is provided. Therefore, also preferably, the number of first magnetic members corresponds to the number of converter units. However, it may also be possible to have more than one first magnetic member allocated to a specific one of the converter units. Moreover, the converter units are usually adapted to the power grid which is usually adapted to be op erated with an alternating voltage. In the present case, the alternating voltage is provided by at least two phases. How ever, a common public power grid has usually three phases, wherein the three phases are deviating by an angle of about 120°.

Each of the converter units is configured to provide an al ternating voltage for each of the phases of the power grid. Therefore, each of the first magnetic members has a number of first limbs corresponding to the number of the phases. Moreo ver, each of the first magnetic members has a first and a second yoke member, wherein the first ends of the first limbs are connected to the first yoke member, and the second ends of the first limbs are connected to the second yoke member. The connection can be provided by contact or the like. The connection can be established by using an adhesive or a clamping member forcing the limbs and the yoke member togeth er in a certain arrangement. The limbs and the yoke members are made from a ferromagnetic material such as iron, nickel, cobalt, an alloy therefrom, or the like. They may also be made from sheets containing one of the before-mentioned com ponents which are insulated against each other. The limbs and the yoke members therefore form a magnetic circuitry for guiding magnetic flux.

Each of the first limbs is provided with a respective first winding having a first end adapted to be connected with a re spective one of the converter units, namely, a respective phase of the respective converter unit. A second end of the first winding is configured to be coupled with a respective one of the phases of the power grid. Therefore, via the in ductive reactance apparatus, each of the converter units is connected with each of the phases of the power grid. Also, all these first windings have the same sense of winding. This allows a proper efficiency with regard to reduction of inter ferences and/or manufacturing the windings and the magnetic members as a module so that the inductive reactance apparatus can be easily assembled by providing a respective number of first magnetic members.

Moreover, the second magnetic member which comprises second limbs and the third and the fourth yoke member may be made from the same material as the first limbs and the first and the second yoke member of the first magnetic members. Howev er, depending on the application, the material may be deviat ing. But it should be considered that the material preferably should be a ferromagnetic material.

The first magnetic members are preferably provided for reduc ing the differential mode interferences. The second magnetic member is preferably provided for reducing common mode inter ferences.

The second magnetic member is coupled to the first magnetic member by connecting the first yoke members with the third yoke member and the second yoke members with the fourth yoke member. Therefore, the second magnetic member adds the mag netic circuitries provided by the first magnetic members such that a single overall magnetic circuitry is provided, wherein the second magnetic member couples the first magnetic mem bers. This allows a very small size of the inductive reac tance apparatus so that costs can be reduced and a high effi ciency can be achieved.

According to the first aspect, the second magnetic member has a number of second limbs corresponding to the number of the phases, wherein first ends of the second limbs are connected to the third yoke member and second ends of the second limbs are connected to the fourth yoke member. Moreover, each of the second limbs is provided with at least one second winding having a first end being connected with at least one, prefer ably all, of the respective first windings which belong to the same phase, and a second end configured to be connected with a respective one of the phases of the power grid. In this way, coupling of the respective first windings with the respective one of the phases of the power grid can be estab lished.

Therefore, an inductive reactance apparatus can be achieved according to the first aspect, which is adapted to reduce differential mode interferences as well as common mode inter ferences at a small size and/or small costs.

In an exemplary embodiment, it is proposed that the sense of the winding of the first windings is inverse to the sense of the winding of the second windings. Especially with regard to the first aspect, this allows a good reduction of the common mode interferences in an easy way. The number of the turns of the windings can be easily resulted by some few experiments, calculation and/or the like. Therefore, the inventive effect can be further improved.

According to a further exemplary embodiment, the second mag netic member has an additional limb without any winding, the additional limb being connected with the third and the fourth yoke member, wherein the sense of the winding of the first windings is the same as the sense of the winding of the sec ond windings. In this embodiment, the additional limb which may be of the same material than the second limbs, allows having the second windings in the same sense than the first windings. Nevertheless, a proper reduction of the common mode interferences can be achieved. The effect of the inductive reactance apparatus according to the invention can be further improved.

Moreover, according to another exemplary embodiment, it is proposed that the connection between at least one of the first yoke members and the third yoke member and/or between least one of the second yoke members and the fourth yoke mem ber comprises an air gap. The air gap allows to adapt the magnetic resistance of the magnetic circuitry so that certain effects can be achieved improving the effect of reduction with regard to interferences. The air gap may depend on the material of the limbs and the yoke members and the magnetic flux which need to be guided by the limbs and the yoke mem bers. Further improvement of the effect with regard to reduc tion of interferences can be achieved.

According to another exemplary embodiment, each of the second windings comprises a number of independent winding portions corresponding to the number of the first windings of a re spective one of the first magnetic members, wherein each of the winding portions is connected with at least one of the respective ones of the first windings. Therefore, the second windings are preferably provided by a number of separated winding portions, wherein each winding portion is allocated to a certain one of the respective first windings or phases, respectively. Therefore, a winding portion may be directly connected with a respective one of the first windings. As the winding portions may belong to different phases, they are preferably insulated against each other. The winding portions have preferably the same sense of winding with regard to each other. Winding portions of different second windings which are allocated to a certain one of the phases of the power grid can be connected directly to the respective one of the phases of the power grid. This construction enhances a good common mode interference reduction.

According to a further exemplary embodiment, for each of the second windings, the first end of the second windings is con nected with the second ends of all of the first windings cor responding to the same phase. In this regard, only one second winding is provided for each of the second limbs. Therefore, a respective connection is provided by the inductive reac tance apparatus. This allows an easy apparatus design which is feasible with regard to handling for connection.

With regard to another exemplary embodiment, the inductive reactance apparatus comprises at least two capacitors, where in one capacitor is provided for each of the phases, wherein a certain one of the at least two capacitors is connected to the first end of the respective second winding. This allows to provide a LCL-filter by the inductive reactance apparatus so that no further components need to be provided in order to realize the desired function. Preferably, the capacitors can be integrated in the inductive reactance apparatus. Moreover, for each of the phases of the power grid, at least one capac itor can be provided. The connection of the capacitors and the windings can be internal of the inductive reactance appa ratus.

In a further exemplary embodiment, the third and/or the fourth yoke member comprises a common mode suppression wind ing. With the common mode suppression winding, it is possible to improve the effect of reducing common mode interferences. The common mode suppression winding can be easily provided on a certain one of the third and/or the fourth yoke member. The common mode suppression winding may be integrated preferably in a neutral line between the power grid and the energy con verter. However, it also may be provided by windings for each of the phases of the power grid which are separated from each other and, preferably, are insulated against each other. At least one winding may be provided for each of the phases.

According to the second aspect of the invention, no second windings need to be provided. For this aspect, it is only necessary to have a common mode suppression winding in order to have reduction with regard to common mode interferences. However, this aspect can be combined with the first aspect.

This is a very easy and simple design which allows a small size and reduced costs. Further, with regard to the second aspect, according to an exemplary embodiment, the second mag netic member has a number of second limbs corresponding to the number of the phases, wherein the first ends of the sec ond limbs are connected to the third yoke member and the sec ond ends of the second limbs are connected to the fourth yoke member, wherein each of the second limbs are provided with at least one second winding having a first end being connected with at least one of the respective first windings and a sec ond end configured to be connected with a respective one of the phases of the power grid, in order to couple the at least one of the respective first windings with a respective one of the phases of the power grid. The effects and the design cor respond to the design and the effects already discussed with regard to the first aspect, which is why it is referred here to.

In an additional exemplary embodiment, at least one of the first limbs is provided with an air gap. This allows to de sign the magnetic circuitry, especially with regard to reduc tion of differential mode interferences. In this regard, also magnetic characteristics as well as the magnetic flux guided by the first limbs can be considered in order to design the air gap. Further improvement of the function of the inductive reactance apparatus can be achieved.

Moreover, according to another exemplary embodiment, at least one of the third and fourth yoke member is provided with an air gap. Preferably, the air gap is provided in one or both connections of the third and fourth yoke member with the first and second yoke members. This allows to design the mag netic coupling between the first and the second magnetic mem ber. The inductive reactance apparatus can be further im proved. The air gap can be realized as discussed above.

One further exemplary embodiment proposes that a housing is provided configured to include the magnetic members and at least one capacitor. Therefore, an integral component can be achieved that can be handled easily by those skilled in the art. Moreover, the housing allows to secure the components against external mechanical and/or atmospheric impacts.

With regard to the energy converter, according to an addi tional exemplary embodiment, the control device is configured to operate the converter units in an interleaved parallel manner. The operation of the interleaved parallel manner al lows reducing a ripple current so that interferences can be reduced. Moreover, with the interleaved operation of the con verter units, the inductive reactance apparatus can be easily adapted to provide proper reduction of the interferences which are emitted by the converter units. Especially with re gard to the interleaved operation of the converter units, a simple and easy inductive reactance apparatus can be achieved so that size and costs can be reduced.

The teaching of the present invention can be readily under stood and at least some additional specific details will ap pear by considering the following detailed description of some exemplary embodiment in conjunction with the accompany- ing drawings. In the drawings, same reference characters cor respond to same components and functions. In the drawings, it is shown:

FIG 1 a schematical block diagram of a structure of a DC- network and a 3-phase power grid being coupled by an energy converter having an inductive reactance apparatus;

FIG 2 a schematically 3-dimensional perspective view of the inductive reactance apparatus according to FIG

1;

FIG 3 a schematic circuitry of the energy converter hav ing two converter units according to a first de sign;

FIG 4 a schematic circuitry as FIG 3 according to a sec ond design;

FIG 5 a schematic 3-dimensional design of an inductive reactance apparatus having an ICT;

FIG 6 a schematic cross-sectional view of the ICT accord ing to FIG 5;

FIG 7 a schematic 3-dimensional view according to FIG 5 of an inductive reactance apparatus having an IICT;

FIG 8 a schematic cross-sectional view of the IICT ac cording to FIG 7;

FIG 9 a schematic block diagram according to FIG 1, wherein the energy converter has three converter units; 10 a schematic block diagram similar to FIG 9, wherein the inductive reactance apparatus is provided as a single integral unit;

11 a schematic side view of a second magnetic member of the inductive reactance apparatus according to FIG 10;

12 a schematic side view of the first magnetic member of the inductive reactance apparatus according to FIG 10;

13 a schematic perspective view of an inductive reac tance apparatus without common mode suppression;

14 a schematic perspective view according to FIG 13, wherein a common mode suppression element is added;

15 a schematic perspective view according to FIG 14, wherein the connections to the converter units and to the grid as well as two capacitors are shown for an energy converter having two converter units;

16 a schematic perspective view similar to FIG 15 for an energy converter having three converter units;

17 a schematic perspective view according to FIG 15 showing magnetic couplings;

18 a schematic diagram of voltages of the three phases of the power grid resulted by an inductive reac tance apparatus according to FIG 11, 12;

19 a schematic diagram of harmonics of the voltages according to FIG 18; FIG 20 a schematic diagram according to FIG 16 resulted by an inductive reactance apparatus according to FIG 11, 13;

FIG 21 a schematic diagram similar to FIG 19 for the con ditions according to FIG 20;

FIG 22 a schematic diagram of voltages according to FIG 20 for an inductive reactance apparatus according to FIG 14;

FIG 23 a schematic diagram similar to FIG 19 and 21 for the conditions according to FIG 22;

FIG 24 a schematic perspective view of an inductive reac tance apparatus having an additional common mode winding based on the design according to FIG 15; and

FIG 25 a schematic perspective view of an inductive reac tance apparatus according to FIG 13 having an addi tional common mode winding.

In the FIG, same reference characters correspond to same com ponents or same functions, respectively.

FIG 1 shows a schematic block diagram of a DC-network 40 and a power grid 20 being electrically coupled by an energy con verter 12 which comprises three converter units 14, 16, 18 (FIG 9) which are connected with the power grid 20 via a LCL- filter 10 as an inductive reactance apparatus.

Each of the converter units 14, 16, 18 is provided by a three-phase inverter which is connected to the DC-network 40 as an energy source, on the one hand, in order to supply electric energy to the power grid 20. On the other hand, all of the three converter units 14, 16, 18 are connected with each of the phases of the power grid 20. For this purpose, each of the converter units 14, 16, 18 pro vides three phases of the power grid 20. Therefore, the con verter units 14, 16, 18 are operated in parallel manner. For this purpose, the converter unit 14, 16, 18 are controlled by a control device 70 which is enclosed by the energy converter 12. Although energy conversion from the DC-network 40 to the power grid 20 is described, a bidirectional power transfer is possible so that the opposite energy direction may be provid ed such that electric energy is supplied from the power grid 20 to the DC-network 40. However, for the purpose of the in vention, the direction of the energy flow is not relevant.

FIG 1, 9 show the structure of the inductive reactance appa ratus 10, namely, inductivities L _c which have a first end connected to a certain phase output of a certain one of the converter units 14, 16, 18, and a second end, wherein the second ends relating to a certain one of the phases of the power grid 20 are connected with each other in order to form nodes 84, 86, 88. Each of the nodes 84, 86, 88 is connected to a first end of one of three capacitors 58, wherein the second ends of the capacitors 58 are connected with each oth er. The before-mentioned nodes 84, 86, 88 are connected to first ends of inductivities L _g , wherein second ends of the inductivities L _g are connected to the respective phases of the power grid 20.

FIG 3 shows in an exemplary embodiment two converter units 14, 16 of the energy converter 12 as discussed above in a first design. FIG 4 shows a second design based on the cir cuitry according to FIG 4. As can be seen from FIG 3 and FIG 4, the LCL-filter 10 from FIG 4 differs from the LCL-filter 10 according to FIG 3 by additional inter cell transformers (ICT) which reduce inter current flows between the different converter units 14, 16, 18.

FIG 5 shows a respective perspective view of a design of the LCL-filter 10 according to FIG 3, wherein FIG 7 shows a re- spective schematic perspective view of the LCL-filter 10 ac cording to FIG 4.

The LCL-filter 10 according to FIG 5 comprises the ICT which is shown in a cross-sectional view in FIG 6. As can be seen from FIG 6, a transformer is provided comprising a magnetic core 72, which is composed of two parts having a general U- shape and forming air gaps 66 at opposing surfaces of the U- shaped portions of the magnetic core 78. About the air gaps 66, windings 74, 76 are provided corresponding to the cir cuitry according to FIG 4. In FIG 6, the air gaps 66 have substantially the same size. However, in differing applica tions, the air gaps 66 may differ from each other.

FIG 8 shows a schematic cross-sectional view of the IICT ac cording to FIG 7. As can be seen from FIG 8, the IICT is based on the ICT according to FIG 6 but it has a magnetic core 78 being formed of two E-shaped core components which are arranged opposed to one another. Between the opposing surfaces, air gaps 66 are provided. The magnetic core 78 pro vides an inner limb 80 as well as two outer limbs 82. The outer limbs 82 are provided with windings 74, 76 according to FIG 8. The inner limb 80 is not provided with any winding.

The design of the IICT according to FIG 8 allows that the in ductivity L _c according to FIG 4 can be avoided.

FIG 10 shows a schematic block diagram according to FIG 9, wherein the inductive reactance apparatus 10 is now provided by a single component. FIG 2 shows a respective 3-dimensional design of the inductive reactance apparatus 10 according to FIG 10.

As can be seen from FIG 2, the inductive reactance apparatus comprises three first magnetic members 22, 24, 26, wherein each one of the first magnetic members 22, 24, 26 is provided for each one of the three converter units 14, 16, 18. Each of the first magnetic members 22, 24, 26 has a number of first limbs 28, 30, 32 which corresponds to the number of the phas- es of the power grid 20, which has a three-phase alternating voltage. Each of the first magnetic members 22, 24, 26 has a first and a second yoke member 34, 36. First ends of the first limbs 28, 30, 32 are connected to the first yoke member 34, and second ends of the first limbs 28, 30, 32 are con nected to the second yoke member 36 (FIG 12).

Moreover, each of the first limbs 28, 30, 32 is provided with a respective first winding 38. Each first winding 38 has a first end adapted to be connected with a respective one of the converter units 14, 16, 18, namely, a respective phase output of the respective of the converter units 14, 16, 18. A second end of the respective first winding is configured to be coupled with a respective one of the phases of the power grid 20, which will be further detailed below. All these first windings 38 have the same sense of winding and also the same number of turns.

In the present case the second ends of the first windings 38 which are allocated to the same phase of the power grid 20, are connected with each other forming the respective notes 84, 86, 88. The notes 84, 86, 88 are not shown in FIG 2 but can be derived from e. g. FIG 10.

The inductive reactance apparatus 10 comprises a second mag netic member 42 (FIG 2, 11) having three limbs 44, 46, 48 corresponding to the number of the phases of the power grid 20. Moreover, the second magnetic member 42 comprises a third and a fourth yoke member 50, 52. First ends of the second limbs 44, 46, 48 are connected to the third yoke member 50 and second ends of the second limbs 44, 46, 48 are connected to the fourth yoke member 52.

Each of the second limbs 44, 46, 48 is provided with at least one second winding 54 having a first end being connected with one of the respective first windings by being connected with one of the respective nodes 84, 86, 88. A second end of the second winding 54 is configured to be connected with a re- spective one of the three phases of the power grid 20, in or der to couple the respective first windings 38 with a respec tive one of the phases of the power grid 20.

Moreover, the yoke members 34, 36, 50, 52 are arranged such that the first yoke members 34 are connected with the third yoke member 50 and the second yoke members 36 are connected with the fourth yoke member 52.

This allows to provide a single magnetic circuitry, wherein all the windings can be coupled magnetically in a certain way. In the present design according to FIG 2, the sense of the winding of the first windings 38 is inverse to the sense of winding of the second windings 54.

The limbs and the yoke members are made of a suitable ferro magnetic material, preferably in the present embodiment a ferrite material, e.g. containing FeC or the like.

In the present embodiment, the connection between the limbs and the yoke members and the connection between the yoke mem ber is provided by direct contact. However, it can be estab lished that a certain air gap may be provided by the connec tion. Especially, it is possible to form the complete first and/or second magnetic member 22, 42 as an integral compo nent. Also, it is possible to form the complete first and second magnetic members 22, 44 as a single integral compo nent. However, depending on the application and the produc tion capabilities, differing designs can be provided.

In the present case, it is further provided that the control device 70 operates the converter units 14, 16, 18 in an in terleaved manner. At the nodes 84, 86, 88, the capacitors 58 are connected with their first ends, wherein their second ends are connected with each other.

FIG 13 shows in a schematically view two first magnetic mem bers 22 which are provided with a third and a fourth yoke member of a second magnetic member 42. The design of FIG 13 may be achieved by providing two first magnetic members 22 according to FIG 12. In FIG 12, the first magnetic members 22 are shown only with two first windings 38 on the outer limbs 28, 32, wherein the inner limb 30 is shown without a winding so that an air gap 90 is visible.

FIG 14 shows the inductive reactance apparatus 10 based on FIG 13, wherein the second magnetic member 42 is added.

FIG 15 shows the inductive reactance apparatus 10 according to FIG 14, wherein additional conductors for the phases of the power grid 20, namely phase A, phase B, and phase C as well as the three respective capacitors 58 are shown connect ed to respective notes 84,86, 88, wherein in FIG 15 only the node 84 is visible.

The inductive reactance apparatus 10 according to FIG 14, 15 is provided for the energy converter 12 having only two con verter units 14, 16. If the energy converter 12 comprises three converter units 14, 16, 18, the inductive reactance ap paratus 10 is adapted according to the schematic perspective view according to FIG 16. This embodiment shows how the in ductive reactance apparatus 10 needs to be adapted according to the number of the converter units 14, 16, 18 of the energy converter 12. The number of the first magnetic members 22 corresponds to the number of the converter units 14, 16, 18. Each of the first magnetic members 22 is allocated to a cer tain one of the converter units 14, 16, 18. Moreover, each of the first magnetic members 22 is adapted to a number of the phases which need to be operated. In the present embodiment, three phases are provided.

FIG 17 shows the inductive reactance apparatus 10 of FIG 15, wherein the magnetic couplings or magnetic fluxes, respec tively, are indicated by arrows 92, 94, 96. Also, from FIG 14, 15, 16, 17, it is apparent that the second magnetic mem ber 42 is connected with the first magnetic members 22, 24 via an air gap 56. The air gap 56 allows adjusting of the coupling.

The arrow 92 represents grid frequency and a n switching fre quency flux, wherein n is the number of interleaved sections. It is noted, that this flows between the phases and can be controlled via the air gaps 56. The arrow 94 shows a magnetic flux having a frequency equal to the switching frequency and flows only between the interleaved windings. The arrow 96 corresponds to a common mode flux that flows during imbalance or due to common mode currents through the energy converter 12.

It can be seen from FIG 17 that the main magnetic flux flows between the interleaved inductor sections formed by the first magnetic members 22 and the grid conductor section formed by the second magnetic member 42 is common mode.

In order to understand the impact of changes, separate simu lations were performed for an energy converter connected us ing the different inductive reactance apparatuses 10 accord ing to FIG 11 through 14.

In this regard, it should be noted that the second magnetic member 42 according to FIG 11 corresponds to the inductivity L _g . The energy converter 12 is operated at a switching fre quency of about 45 kHz and each simulation uses the same con troller and grid connection. Moreover, core sizes and air gaps in all designs are substantially the same and the terms of the windings are also substantial equal. In order to un derstand the effect of common mode current, the second ends of the capacitors 58 which are connected with each other, are also connected with a high-impedance to ground.

The following FIG 18 through 23 show simulations of the in ventive inductive reactance apparatus. FIG 18 shows a schematic diagram of a three-phase voltage.

FIG 19 shows a schematic diagram of harmonics of the three- phase voltage according to FIG 18. It can be noted that there is a significant common mode current in all of the three phases of about 2 A peak. In the design with a multi-phase inductivity as shown in FIG 11 and 13, the respective voltag es are shown in FIG 20, showing a respective diagram as FIG 18, and FIG 21 shows a respective diagram as FIG 19 for the three-phase voltage according to FIG 20. According to this embodiment, the common mode current has increased despite the connection between the phases. There is less common mode re duction than with the additional core section or second mag netic member 42, repsectively. The best design according to the simulation appears to be with the combined inductivity according to FIG 14. A respective three-phase voltage is shown in a schematic diagram according to FIG 22 similar as FIG 18 and 20. The respective harmonics are shown in a dia gram according to FIG 23 similar as FIG 19 and 21. A signifi cant reduction with regard to the common mode current can be achieved. This is shown according to FIG 22, showing a re spective diagram as FIG 18 and 20.

In the FIG 18, 20, 22, the abscissa is allocated to the time and the ordinate is allocated to the voltage.

It should be noted that the simulations according to FIG 18, 20, 22 start at 0.3 s and a load step at 0.75 s.

In order to compare the harmonic performance of the combined inductor design or inductive reactance apparatus a fourier transform is made from the embodiments according to FIG 18 and 22. The results are shown in respective diagrams 19, 21, showing schematic diagrams of harmonics, wherein the abscissa is allocated to the order of harmonics and the ordinate is allocated to a normalized magnitude.

As can be derived from these drawings, the design according to FIG 14 offers more than 80 % reduction of common mode in- terference and also allows improving slightly the filtering of switching components, while also offering a reduced volume and weight of the complete component.

In order to further increase the common mode inductivity, an additional common mode winding 60 can be provided which is wound around the common mode core sections as shown in FIG 24. FIG 24 shows a schematic three-dimensional view according to FIG 14 wherein the common mode winding 60 is additionally provided as well as air gaps 68 forming an inductive reac tance apparatus 62. The common mode windings 60 may be pro vided separately for each of the phases. The design according to the FIG 24 is especially provided for use of an interleav ed modus. Similar to the common mode inductivities, the com mon mode windings can be formed by wrapping all three phases around the common core of the second magnetic member 42. Alt hough the winding 60 is only shown in an upper portion of the second magnetic member 42, it may be also provided in a lower portion of the second magnetic member 42. Also, it is possi ble to provide the winding 60 at both portions of the second magnetic member 42. The winding 60 is preferably arranged at a portion of the magnetic core that is intended to be con nected with the first magnetic members 22. It should also be noted that, in FIG 24, the core is shown very wide. However, the actual core section between the two inductivities could be smaller and the size can be independent from other core sections, especially having in view that preferably only the common mode flux will pass there between.

A respective design for a non-interleaved application is shown in the schematic three-dimensional view according to FIG 25 which is based on the design of FIG 13. As can be de rived from FIG 25, the additional common mode winding 60 is provided at the third or the fourth yoke member 50, 52. How ever, it may also be provided at both of the third and fourth yoke members 50, 52. FIG 25 shows an inductive reactance apparatus 64 based on the design according to FIG 13 having also a common mode winding 60. This design is directed to be used with non-interleaved operated converter units 14, 16.

The invention allows a smaller size and weight of the induc tive reactance apparatus. Moreover, a better harmonic perfor mance, especially in view of common mode filtering, can be achieved. Moreover, a common mode inductance allows improving performance during startup and transients.

The invention allows the design of the inductive reactance apparatus to be improved by an additional core section, name ly, the second magnetic member 42 in order to allow integra tion to an LCL-circuit 10 without a third inductivity stage. The proposed designs do not require such a stage. Only small call sections are required to connect the inductor stages. Therefore, the inductive reactance apparatus can be designed light-weighted due to the reduction of core material.

The invention allows also a design e.g. according to FIG 14 to offer additional common mode filtering that is not offered in previous designs of the art. The integration with an LCL- Filter also offers a better filtering of switching harmonics compared to pure inductive solutions.

One issue with the coupled inductors is that the resulting AC-inductance is small for basic frequency, for example 50 Hz, resulting in high speed. Also, impedance is offered during startup or during transience. The proposed design will result in a higher overall inductance to improve the control lability of the converter during these situations.

Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the inde- pendent claims, and not solely the combinations explicitly set out in the claims.

It is also observed during that, while the above described exemplary embodiments of the invention, this description should not be regarded as limiting the scope. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the dependent claims.

Reference characters

10 inductive reactance apparatus

12 energy converter

14 converter unit

16 converter unit

18 converter unit

20 power grid

22 first magnetic member

24 first magnetic member

26 first magnetic member

28 first limb

30 first limb

32 first limb

34 first yoke member

36 second yoke member

38 first winding

40 DC-network

42 second magnetic member

44 second limb

46 second limb

48 second limb

50 third yoke member

52 fourth yoke member

54 second winding

56 air gap

58 capacitor

60 common mode winding

62 inductive reactance apparatus

64 inductive reactance apparatus

66 air gap

68 air gap

70 control device

72 magnetic core 74 winding

76 winding

78 magnetic core

80 inner limb 82 outer limb

84 node 86 node 88 node 90 air gap 92 arrow

94 arrow

96 arrow