Low-mass inductive filtering device

Abstract

The invention relates to an inductive filtering device comprising a closed magnetic core (12) formed around a central recess (14) and at least one electrical conductor (16) wound around the magnetic core (12) so as to pass through the central recess (14), the electrical conductor (16) extending along a curved main axis (20) suitable for the winding, wherein the electrical conductor (16) has a first portion (16a) arranged in the central recess (14) and a second portion (16b) arranged outside the central recess (14), wherein a section of the first portion (16a) is defined perpendicularly to the main axis in the portion in question and a section of the second portion (16b) is defined perpendicularly to the main axis in the portion in question, and wherein a surface area of the first section is smaller than a surface area of the second section.

Description

DESCRIPTION Title of the invention: Reduced mass inductive filtering device

[0001] The invention relates to an inductive filtering device. This type of filtering is commonly used to reduce possible disturbances present on an electrical conductor. The device is then placed in series with the conductor and behaves like a low-pass filter by attenuating high-frequency disturbances.

[0002] The invention finds particular utility in the aeronautical field where the current trend is to increase the number of electrical equipment and therefore the on-board electrical power.

[0003] An aircraft generally includes a large number of electrical loads powered by an on-board electrical supply network. For example, the aircraft's flight controls, air conditioning systems and internal lighting use three-phase AC electrical machines. The electrical energy supplied to these machines comes from power converters connected to an on-board network delivering electrical energy in direct or alternating form. The on-board network may include, for example, electrical generators, storage batteries, or even means of connection to an electrical supply network external to the aircraft and enabling the aircraft to be powered when parked at an airport. 540V DC networks and / or 115V or 230V 400Hz AC networks are commonly found on board aircraft.As is known, power converters receive energy from the on-board network to convert it into polyphase alternating energy adapted to the power and frequency requirements of the load. When a converter is powered by an AC network, the converter comprises, for example, a rectifier delivering a DC voltage followed by an inverter producing the AC voltage required for the load from the DC voltage. When a converter is powered by a DC network, the converter then comprises a circuit fulfilling the inverter function and producing the AC voltage directly from the DC voltage of the on-board network. A converter can be dedicated to a load or common to several loads.

[0004] The electromagnetic compatibility of the various electrical and electronic equipment on board an aircraft is a delicate problem that becomes all the more important as the number of equipment is large and the power consumption is high. More specifically, to limit the on-board mass, it is common to implement static converters including electronic switches. Examples include inverters operating in pulse width modulation to generate an alternating voltage. The switching frequency is much higher than the frequency of the useful alternating voltage generated by the inverter. The presence of this switching frequency tends to create high-frequency disturbances that tend to propagate on the on-board networks. To limit this propagation, it is common to implement inductive filters at the input and / or output of the various converters.Depending on their connection, these filters can filter both common mode and differential mode disturbances.

[0005] Inductive filters are generally composed of a winding of conductive wires arranged around a magnetic core. It is possible to wind only one wire around a magnetic core. It is also possible to wind several wires around the same magnetic core, in particular to circulate the different input or output phases of a converter. Whether there is only one wire or several wires around the same core, these wires must allow the transport of the electrical power of the phase in question. To this end, the greater the electrical powers, the larger the wire cross-sections must also be in order to limit Joule effect losses in the wires. The dimensions of the magnetic cores also follow those of the wound wires in order to accommodate the wires. Consequently, the dimensions and masses of inductive filters are important.

[0006] In many vehicles, and particularly in aircraft, reducing on-board mass is a recurring problem. The current trend towards increasing on-board electrical equipment therefore tends to increase the mass of the filters required for the proper functioning of the on-board electrical system.

[0007] The invention aims to overcome all or part of the problems mentioned above by proposing an inductive filter of reduced dimensions and mass compared to a conventional filter.

[0008] To this end, the invention relates to an inductive filtering device comprising a single-piece magnetic core formed around a central recess and at least one electrical conductor wound around the magnetic core passing through the central recess, the electrical conductor extending along a curved main axis suitable for winding, in which the electrical conductor has a first part arranged in the central recess and a second part arranged outside the central recess, in which a section of the first part is defined perpendicular to the main axis in the part in question and a section of the second part perpendicular to the main axis in the part in question, and in which a surface area of ​​the section of the first part is less than a surface area of ​​the section of the second part.The central recess extends along an axis and a surface area of ​​a section of the central recess, a section defined perpendicular to the axis of the central recess, is less than a surface area included in a smaller closed curve which can surround as many second parts, all arranged parallel to each other along their main axis, as the number of times the electrical conductor crosses the central recess along its axis.

[0009] According to one embodiment, the electrical conductor comprises an electrical wire of constant cross-section along its main axis and a protrusion made of electrically conductive material forming the second part. The protrusion is for example formed of an electrically conductive sleeve fitted onto the electrical wire to form the second part, of at least one section of a second electrical wire fixed to the first electrical wire to form the second part, of a strip wound around the electrical wire.

[0010] According to one embodiment, the magnetic core is closed.

[0011] The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:

[0012] Figure 1 represents an example of an inductive filter according to the invention and having only one electrical conductor:

[0013] Figure 2 shows an electrical conductor suitable for the filter of Figure 1;

[0014] Figure 3 illustrates the reduction in dimensions of a magnetic core of an inductive filter according to the invention;

[0015] Figure 4 represents an example of an inductive filter according to the invention and having two separate electrical conductors;

[0016] Figures 5 to 7 represent several examples of electrical conductors which can be implemented in an inductive filter according to the invention and in particular those illustrated by Figures 1 and 3;

[0017] Figure 8 shows a strip that can be wound around an electric wire to form an electric conductor that can be used in an inductive filter according to the invention.

[0018] For the sake of clarity, the same elements will have the same references in the different figures.

[0019] Figure 1 shows an inductive filter 10 comprising a single-piece magnetic core 12 formed around a central recess 14 and an electrical conductor 16. The magnetic core 12 is tubular in shape and extends around an axis 18. The magnetic core 12 is formed from a single mechanical part without assembly. The central recess 14 develops around the axis 18. In the example shown in Figure 1, the central recess 14 has a circular section perpendicular to the axis 18. Within the scope of the invention, the section of the central recess 14 can take any other shape, for example rectangular, triangular, etc.

[0020] The magnetic core 12 can be closed, that is to say without a physical air gap. This type of core is usually called "toroidal" by many manufacturers of magnetic cores. This term "toroidal" goes well beyond the shape of a torus as defined mathematically. In particular, there are so-called toroidal magnetic cores of cylindrical shape with a circular or rectangular cross-section, etc. Some materials used to produce magnetic cores are well suited to a shape without an air gap. In particular, we can cite certain nanocrystalline ferromagnetic materials produced by filament winding around the axis 18. This type of material is particularly well suited to filtering because it has a very strong relative magnetic permeability range which can be greater than 30,000.

[0021] Alternatively, the single-piece magnetic core 12 may have a physical air gap, in particular to limit the risk of saturation of the magnetic core. The air gap may be formed by a slot opening the magnetic core.

[0022] A non-monobloc magnetic core, i.e. made in several parts, would make it easier to install the electrical conductor 16, in particular for an electrical conductor 16 having a shape such as defined by the invention as will be seen later. For example, it is possible to assemble two parts in the shape of the letter U whose respective ends are fixed to each other. The joint plane connecting the two parts may contain the axis 18 of the central recess 14. The joint plane may be parallel to the axis 18. On the other hand, even if the fixing of the different parts of the magnetic core is carried out with the greatest proximity, there always remains an uncontrolled residual air gap between the parts leading to magnetic losses.We will see later that a single-piece magnetic core without an air gap or with a thin air gap complicates the installation of the electrical conductor 16 according to the invention but that there are means to ensure this installation.

[0023] The electrical conductor 16 extends along a curved main axis 20 adapted to be wound around the magnetic core 12 by crossing the central recess 14. In the example shown, the electrical conductor 16 crosses the central recess 14 twice. The electrical conductor 16 thus forms two turns around the magnetic core 12. The invention can be implemented regardless of the number of turns and therefore the number of passages of the electrical conductor 16 through the central recess 14. According to the invention, the section of the electrical conductor 16, section defined perpendicular to the axis 20, is not constant and varies along the axis 20. More precisely, the part of the electrical conductor 16 located inside the central recess 14 has a smaller surface area of ​​its section than the surface area of ​​the section outside the central recess 14.

[0024] At first glance, a reduction in the cross-section of the electrical conductor 16 may appear to cause disadvantages, in particular an increase in the resistance of the electrical conductor 16 locally where the section is reduced and therefore local heating of the electrical conductor 16 by Joule effect during the passage of electric currents conducted by the electrical conductor 16. However, local heating can be compensated by a transfer of heat from the parts of the electrical conductor 16 where the section is reduced to the parts of the electrical conductor 16 where the section is larger. Overall, to limit the increase in the overall resistance of the electrical conductor 16, it is possible to compensate for the increase in resistance due to the reduced section inside the central recess 14 by an increase in the section of the electrical conductor 16 for its parts located outside the central recess 14.

[0025] The invention has the advantage of allowing the dimensions of the magnetic core 12 to be reduced. More precisely, by reducing the section of the electrical conductor 16 in the central recess 14, it is possible to reduce the section of the central recess 14, section defined perpendicular to the axis 18 and consequently the external dimensions of the magnetic core 12, dimensions perpendicular to the axis 18. For example, if the magnetic core 12 has a cylindrical shape with a circular section as shown in FIG. 1, the internal diameter of the magnetic core 12, diameter of the central recess 14, is reduced. Similarly, the external diameter of the magnetic core 12 is also reduced.

[0026] In the case where the magnetic core 12 comprises a physical air gap formed by a slot, the thickness of the slot remains less than a smaller dimension of the reduced section of the electrical conductor, section located inside the central recess 14. Indeed, to obtain a reduction in the risk of saturation of the magnetic core 12, a small air gap already provides a notable reduction in the risk of saturation.

[0027] Figure 2 shows the electrical conductor 16 alone outside the magnetic core 12. The axis 20 is rectilinear in Figure 2. It is understood that the axis 20 is curved when the electrical conductor 16 is wound around the magnetic core 12. The electrical conductor 16 comprises two different parts: 16a called small section and 16b called large section. The parts 16a are of circular section with a diameter d smaller than the diameter D of the circular section of the parts 16b. The parts 16a are intended to be arranged inside the central recess 14 and the parts 16b outside the central recess 14 when the electrical conductor 16 is wound around the magnetic core 12.

[0028] The reduction of the internal diameter of the central recess 14 is characterized by the fact that the surface area of ​​the section S of the central recess 14 is less than the surface area delimited by the smallest curve C that can surround as many large sections of juxtaposed electrical conductors as there are passages of the electrical conductor 16 passing through the central recess 14. The large section of the electrical conductor 16 is defined for the parts 16b intended to be arranged outside the central recess 14. In other words, it would not be possible to juxtapose as many parts 16b of the electrical conductor 16 in the central recess 14. This characteristic is illustrated in Figure 3 where the electrical conductor 16 passes through the central recess 14 seven times. On the right-hand side of Figure 3, the magnetic core 12 is shown in a top view along the axis 18 and seven parts 16a can be seen inside the central recess 14.The axes 20 of the seven parts 16a are substantially parallel to the axis 18 of the central recess 14. On the left part of Figure 3, seven parts 16b are grouped in contact with each other, the axes 20 of the different parts 16b being parallel to each other. This grouping is unlikely to exist in a real filtering device. This fictitious grouping has the simple purpose of explaining the volume that the electrical conductor would occupy if it did not include a part 16a with a small section and if its section were constant, like that of the part 16b. A curve C shown in dotted lines surrounds the seven parts 16b as closely as possible. The surface area included inside the curve C is larger than the surface area S of the section of the central recess 14. The curve C can be extrapolated regardless of the number of times that the conductor 16 crosses the central recess.Figuratively, curve C could be a tight rubber band surrounding as many 16b parts as the number of times conductor 16 crosses the central recess.

[0029] Geometrically, the magnetic core 12 can be characterized by its magnetic length L shown in dotted lines in Figures 1 and 3. Generally, the magnetic length is the average length of the magnetic field lines circulating in the magnetic core. When a coil is wound around a toroidal magnetic core passing through the central recess, and when the magnetic core is made of a homogeneous material, the magnetic length is substantially the length of the average fibers surrounding the central recess. In the example shown in Figure 1, the central recess 14 has a circular section perpendicular to axis 18 and the magnetic length L is the perimeter of a circle whose center is located on axis 18. Generally, the magnetic length L is used to apply Ampère's law macroscopically: HL = ni (1 )

[0030] H represents the magnetic excitation before saturation and i represents the current flowing in n turns wound around the magnetic core 12. The invention makes it possible to reduce the magnetic length L of the magnetic core 12. For a given number of turns, by reducing the magnetic length L, the inductance of the inductive filter 10 increases. Generally speaking, the filtering efficiency of the inductive filter 10 is all the better as the inductance is high. Consequently, the invention makes it possible to improve the efficiency of an inductive filter. Alternatively, if it is desired to maintain the same efficiency, it is possible to reduce other dimensions of the magnetic core 12, for example its external diameter or its height defined along the axis 18.

[0031] Figure 4 shows an example of an inductive filter 30 according to the invention having a magnetic core 32 with a central recess 34 as well as two separate electrical conductors 36 and 38 both passing through the central recess 34. This type of filter is well suited to filtering common mode disturbances of two phases of an electrical energy converter, for example to filter the two input phases of an inverter. The invention can of course be implemented for more than two electrical conductors passing through the central recess 34 of the same magnetic core 32. It is for example possible to provide three electrical conductors passing through the same magnetic core and in each of which circulates an output phase of a three-phase inverter.

[0032] In the example shown, each of the electrical conductors 36 and 38 makes only one passage through the central recess 34, each forming a turn around the magnetic core 32. It is of course possible for each of the electrical conductors to pass through the central recess 34 several times, forming as many turns as there are crossings.

[0033] As in the filter 10, each of the electrical conductors 36 and 38 comprises at least one part, respectively 36a and 38a of small section and several parts respectively 36b and 38b. The small sections 36a and 38a are arranged in the central recess 34 and the large sections 36b and 38b are arranged outside the central recess 34.

[0034] By implementing a magnetic core made in several parts, it is possible to arrange the electrical conductor(s) around only one part of the magnetic core with as many turns as necessary and then to assemble the different parts of the magnetic core in order to obtain the so-called closed magnetic core. Before closing, the small section parts will be placed along one face of the magnetic core, a face forming after closing a face of the central recess.

[0035] On the other hand, by using a single-piece magnetic core, i.e. manufactured in the form of a closed ring or having a small physical air gap, it is possible to produce the filter by winding a wire of constant section around the magnetic core and then enlarging the section of parts of the wire outside the central recess to form the parts of large section.

[0036] Figures 5 to 7 represent several examples of electrical conductors particularly suitable for magnetic cores without an air gap or with a thin air gap that does not allow the winding to be carried out before being placed around the magnetic core. It is however possible to implement these examples of electrical conductors with assembled magnetic cores. Generally, the electrical conductors shown in Figures 5 to 7 comprise protrusions made of electrically conductive material forming the second parts 16b.

[0037] Figure 5 shows an electrical conductor 40 formed from an electrical wire 42 of constant section extending in the figure along an axis 44 similar to the axis 20. As in Figure 2, the axis 44 is here rectilinear. The axis 44 is intended to be curved during winding around the magnetic core to form an inductive filter according to the invention. This is also applicable to the electrical conductors shown in Figures 6 and 7.

[0038] The electrical conductor 40 comprises, in addition to the electrical wire 42, several sleeves 46 made of electrically conductive material. The sleeves have a tubular shape extending along the axis 44 and the inner face of which is adjusted to the outer face of the electrical wire. The electrical wire 42 and the sleeves 46 can have circular sections perpendicular to the axis 46. The outer diameter of the sleeves can then form the diameter D of the parts 16b shown in Figure 2. Between the sleeves 46, the electric wire remains bare to form the parts 16a shown in Figure 2.

[0039] The installation of an electrical conductor 40 in an inductive filter using a single-piece magnetic core can be easily carried out by placing the electrical wire 42 in the central recess and then by threading two sleeves 46 onto the electrical wire 42 on either side of the central recess. If the inductive filter comprises several turns, a sleeve 46 is threaded onto the electrical wire 42 after each passage of the electrical wire in the central recess. After threading a sleeve 46 onto the electrical wire, it is possible to fix the sleeve in question to the electrical wire, for example by brazing it.

[0040] Before installing an electrically conductive sleeve 42, it is possible to cover the electrical wire, in its part 16a, with another insulating sleeve in order to avoid any electrical contact between the different parts 16a if the filter comprises several turns or in order to avoid any electrical contact between a part 16a and the magnetic core. In the same way, it is also possible to cover the conductive sleeves 42 with insulating sleeves.

[0041] Figures 6 and 7 show electrical conductors, respectively 50 and 60 in which the parts 16b are formed by sections 52 of electrical wire 52 fixed to an electrical wire 42. The electrical conductor 50 shown in Figure 6 comprises one section 52 per part 16b and the electrical conductor 60 shown in Figure 7 comprises several sections 52 per part 16b. As for the electrical conductor 40 shown in Figure 5, for an implementation with a single-piece magnetic core, for each part 16b, it is possible to fix the section(s) 52 to the electrical wire 42 after passing the electrical wire 42 through the central recess. Furthermore, it is possible to electrically insulate the outer face of the electrical conductors 50 and 60, either by means of separate insulating sleeves for the parts 16a and 16b, or a single insulating sleeve covering the entire electrical conductor, or an insulating sleeve per part.

[0042] Figure 8 shows a strip that can be wrapped around an electric wire to form an electrical conductor suitable for magnetic cores monoblocs that can be implemented in an inductive filter according to the invention. To form a part 16b, it is possible to wind the strip 70 around an electric wire 42. The strip 70 can be wound in several turns around the electric wire 42. The different turns can completely overlap until reaching a desired external diameter of the part 16b. The width I of the strip is then equal to the length L of the part 16b, length defined along the axis 44. Alternatively, it is possible to provide a partial overlap of each layer of strip in order to obtain a length L of the part 16b greater than the width I of the strip 70.

Claims

CLAIMS 1. Inductive filtering device comprising a single-piece magnetic core (12) formed around a central recess (14) and at least one electrical conductor (16) wound around the magnetic core (12) passing through the central recess (14), the electrical conductor (16) extending along a curved main axis (20; 44) adapted to the winding, in which the electrical conductor (16) has a first part (16a) arranged in the central recess (14) and a second part (16b) arranged outside the central recess (14), in which a section of the first part (16a) is defined perpendicular to the main axis in the part considered and a section of the second part (16b) perpendicular to the main axis in the part considered, in which a surface area of ​​the section of the first part is less than a surface area of ​​the section of the second part,in which the central recess (14) extends along an axis (18) and in which a surface area of ​​a section (S) of the central recess (14), a section defined perpendicular to the axis (18) of the central recess (14) is less than a surface area included in a smaller closed curve (C) capable of surrounding as many second parts (16b), all arranged parallel to each other along their main axis (20), as times the electrical conductor (16; 40; 50; 60) crosses the central recess (14) along its axis (18)., 2. Inductive filtering device according to claim 1, in which the electrical conductor (40) comprises a first electrical wire (42) of constant section along its main axis (44) and a protrusion (46; 52; 70) made of electrically conductive material forming the second part (16b).

3. Inductive filtering device according to claim 2, wherein the protrusion is formed of an electrically conductive sleeve (46) fitted over the electrical wire (42) to form the second part (16b).

4. Inductive filtering device according to claim 2, wherein the protrusion is formed from at least one section (52) of a second electrical wire fixed to the first electrical wire (42) to form the second part (16b).

5. Inductive filtering device according to claim 2, in which the protrusion is formed from a strip (70) wound around the electric wire (42).

6. Inductive filtering device according to one of the preceding claims, in which the magnetic core is closed.

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