Reduced-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) passing through the central recess (14), the electrical conductor (16) extending along a curved principal axis (20) adapted for winding, wherein the electrical conductor (16) has a first portion (16a) disposed within the central recess (14) and a second portion (16b) disposed outside the central recess (14), wherein a section of the first portion (16a) is defined perpendicular to the principal axis in the considered portion and a section of the second portion (16b) is defined perpendicular to the principal axis in the considered portion, and wherein an area of ​​the first section is smaller than an area of ​​the second section. Figure for the abstract: Fig. 1.

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 potential disturbances present on an electrical conductor. The device is placed in series with the conductor and behaves as a low-pass filter by attenuating high-frequency disturbances.

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

[0003] An aircraft typically includes a large number of electrical loads powered by an onboard electrical supply network. For example, the aircraft's flight controls, air conditioning, and interior lighting systems utilize three-phase AC electrical machines. The electrical energy supplied to these machines comes from power converters connected to an onboard network that delivers electrical energy in direct or alternating current form. The onboard network may include, for example, electric generators, storage batteries, or means of connection to an external power supply network, enabling the aircraft to be powered when parked at an airport. Typically, aircraft use 540V DC networks and / or 115V or 230V 400Hz AC networks.Power converters, as is well known, receive energy from the vehicle's electrical system and convert it into polyphase alternating current (AC) suitable for the power and frequency requirements of the load. When a converter is powered by an AC system, it typically includes a rectifier that delivers a direct current (DC) voltage, followed by an inverter that produces the AC voltage required by the load from the DC voltage. When a converter is powered by a direct current (DC) system, it includes a circuit that acts as an inverter and produces the AC voltage directly from the DC voltage of the vehicle's electrical system. A converter can be dedicated to a single load or shared by several loads.

[0004] The electromagnetic compatibility of the various electrical and electronic equipment carried on board an aircraft is a delicate problem that becomes increasingly important as the number of devices increases and power consumption increases. More specifically, to limit the onboard mass, it is common to implement static converters incorporating electronic switches. Examples include pulse-width modulation (PWM) inverters that 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 can propagate through onboard networks. To limit this propagation, it is common practice 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, particularly for carrying 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 transmission of the electrical power of the phase in question. To this end, the higher the electrical power, the larger the wire cross-sections must also be in order to limit Joule heating losses in the wires. The dimensions of the magnetic cores also correspond to those of the wound wires in order to accommodate the wires. Consequently, the dimensions and masses of inductive filters are significant.

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

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

[0008] To this end, the invention relates to an inductive filtering device comprising a closed magnetic core formed around a central recess and at least one electrical conductor wound around the magnetic core through the central recess, the electrical conductor extending along a curved principal axis adapted to the winding, in which the electrical conductor has a first part disposed in the central recess and a second part disposed outside the central recess, in which a section of the first part is defined perpendicular to the principal axis in the part considered and a section of the second part perpendicular to the principal axis in the part considered, and in which an area of ​​the first section is less than an area of ​​the second section.

[0009] Advantageously, the central recess extends along an axis and a surface of a section of the central recess, a section defined perpendicular to the axis of the central recess, is smaller than a surface contained in a smaller closed curve that can enclose as many second parts, all arranged parallel between them along their main axis, how many times does the electrical conductor cross the central recess along its axis.

[0010] According to one embodiment, the electrical conductor comprises an electrical wire of constant cross-section along its main axis and an electrically conductive sleeve fitted onto the electrical wire to form the second part.

[0011] According to another embodiment, the electrical conductor comprises a first electrical wire of constant cross-section along its main axis and at least one section of a second electrical wire fixed to the first electrical wire to form the second part.

[0012] According to yet another embodiment, the electrical conductor comprises an electrical wire of constant cross-section along its main axis and a strip wrapped around the electrical wire.

[0013] The invention will be better understood and other advantages will become apparent upon reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which:

[0014] [Fig. 1] represents an example of an inductive filter according to the invention and having only one electrical conductor:

[0015] [Fig.2] represents an electrical conductor adapted to the filter of [Fig.1];

[0016] [Fig.3] illustrates the reduction in dimensions of a magnetic core of an inductive filter according to the invention;

[0017] [Fig.4] represents an example of an inductive filter according to the invention and having two separate electrical conductors;

[0018] Figures 5 to 7 represent several examples of electrical conductors that can be used in an inductive filter according to the invention, and in particular those illustrated by Figures 1 and 3;

[0019] [Fig.8] represents a strip that can be wrapped around an electrical wire to form an electrical conductor that can be used in an inductive filter according to the invention.

[0020] For the sake of clarity, the same elements will bear the same references in the different figures.

[0021] Figure 1 shows an inductive filter 10 comprising a closed 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 central recess 14 extends around the axis 18. In the example shown in Figure 1, the central recess 14 has a circular cross-section perpendicular to the axis 18. Within the scope of the invention, the cross-section of the central recess 14 can take any other shape, for example rectangular, triangular, etc.

[0022] The magnetic core 12 may be without an air gap. This type of core is usually called "toric" by many magnetic core manufacturers. This term The term "toric" goes well beyond the mathematically defined shape of a torus. Magnetic cores, also called toric, can be cylindrical with a circular or rectangular cross-section. Some materials used to create magnetic cores are well-suited to a shape without an air gap. Notable examples include certain nanocrystalline ferromagnetic materials produced by filament winding around the 18-axis. This type of material is particularly well-suited for filtering because it possesses a very high relative magnetic permeability range, which can exceed 30,000.

[0023] Alternatively, the magnetic core 12 may have an air gap. More specifically, the magnetic core may be made of several parts assembled to form the magnetic core 12. For example, it is possible to assemble two U-shaped parts whose respective ends are fixed to each other. The parting plane connecting the two parts may contain the axis 18 of the central recess 14. The parting plane may be parallel to the axis 18.

[0024] A magnetic core made of several parts facilitates the installation of the electrical conductor 16, particularly for an electrical conductor 16 having a shape such as that defined by the invention, as will be seen later. However, even if the different parts of the magnetic core are fixed as close together as possible, a residual air gap always remains between the parts, resulting in magnetic losses. It will be seen later that a magnetic core without an air gap complicates the installation of the electrical conductor 16 according to the invention, but that there are means to ensure this installation.

[0025] The electrical conductor 16 extends along a curved principal axis 20 adapted for winding around the magnetic core 12, passing through the central recess 14. In the example shown, the electrical conductor 16 passes through 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 times the electrical conductor 16 passes through the central recess 14. According to the invention, the cross-section of the electrical conductor 16, defined perpendicular to the axis 20, is not constant and varies along the axis 20. More precisely, the portion of the electrical conductor 16 located inside the central recess 14 has a smaller cross-sectional area than the cross-sectional area outside the central recess 14.

[0026] At first glance, a reduction in the cross-section of the electrical conductor 16 may appear to lead to disadvantages, notably an increase in the resistance of the electrical conductor 16 locally where the cross-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 mitigated by heat transfer from the reduced cross-sectional areas of the electrical conductor 16 to the larger cross-sectional areas. To limit the overall increase in resistance of the electrical conductor 16, the increased resistance due to the reduced cross-sectional area within the central recess 14 can be compensated for by increasing the cross-sectional area of ​​the conductor 16 outside the central recess 14.

[0027] The invention has the advantage of allowing the reduction of the dimensions of the magnetic core 12. More specifically, by reducing the cross-section of the electrical conductor 16 in the central recess 14, it is possible to reduce the cross-section of the central recess 14, a cross-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 cross-section as shown in [Fig. 1], the inner diameter of the magnetic core 12, the diameter of the central recess 14, is reduced. Similarly, the outer diameter of the magnetic core 12 is also reduced.

[0028] Figure 2 shows the electrical conductor 16 alone outside the magnetic core 12. The axis 20 is straight 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, referred to as the smaller section, and 16b, referred to as the larger section. The parts 16a have a circular cross-section with a diameter d smaller than the diameter D of the circular cross-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.

[0029] Reducing the internal diameter of the central recess 14 is not mandatory. When implemented, the reduction can be characterized by the fact that the cross-sectional area S of the central recess 14 is less than the area delimited by the smallest curve C that can enclose as many large cross-sections of juxtaposed electrical conductors as there are passages of the electrical conductor 16 through the central recess 14. The large cross-section of the electrical conductor 16 is defined for the portions 16b intended to be arranged outside the central recess 14. In other words, it would not be possible to juxtapose as many portions 16b of the electrical conductor 16 within the central recess 14. This characteristic is illustrated in [Fig. 3] where the electrical conductor 16 passes through the central recess 14 seven times. On the right-hand side of [Fig.3], the magnetic core 12 is shown in top view along axis 18 and seven parts 16a are distinguished 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 . In the left-hand side of [Fig. 3], seven sections 16b are grouped together in contact with each other, the axes 20 of the different sections 16b being parallel to each other. This grouping is unlikely to exist in a real filtering device. This hypothetical grouping serves simply to illustrate the volume that the electrical conductor would occupy if it did not include a section 16a with a small cross-section and if its cross-section were constant, like that of section 16b. A dashed curve C closely encircles the seven sections 16b. The area enclosed within curve C is larger than the area S of the cross-section of the central recess 14. Curve C can be extrapolated regardless of the number of times the conductor 16 passes through the central recess. Figuratively speaking, curve C could be a tight elastic band surrounding as many parts 16b as there are times conductor 16 crosses the central recess.

[0030] Geometrically, the magnetic core 12 can be characterized by its magnetic length L, represented by dashed 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 approximately the length of the average fibers surrounding the central recess. In the example shown in [Fig. 1], the central recess 14 has a circular cross-section perpendicular to the axis 18, and the magnetic length L is the perimeter of a circle whose center lies on the axis 18. Generally, the magnetic length L is used to macroscopically apply Ampère's law: HL = ni(l)

[0031] 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, reducing the magnetic length L increases the inductance of the inductive filter 10. In general, the filtering efficiency of the inductive filter 10 is higher when the inductance is greater. 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 outer diameter or its height defined along the axis 18.

[0032] Figure 4 shows an example of an inductive filter 30 according to the invention having a magnetic core 32 with a central recess 34 and two separate electrical conductors 36 and 38 both passing through the central recess 34. This type of filter is well suited for filtering common-mode disturbances of two phases of an electrical power converter, for example for filtering 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 flows an output phase of a three-phase inverter.

[0033] In the example shown, each of the electrical conductors 36 and 38 makes only one pass through the central recess 34, each forming a loop around the magnetic core 32. It is of course possible that each of the electrical conductors passes through the central recess 34 several times, forming as many loops as there are crossings.

[0034] As in the filter 10, each of the electrical conductors 36 and 38 comprises at least one portion, respectively 36a and 38a, of small cross-section and several portions respectively 36b and 38b. The small cross-sections 36a and 38a are arranged in the central recess 34 and the large cross-sections 36b and 38b are arranged outside the central recess 34.

[0035] By using a magnetic core made of several parts, it is possible to arrange the electrical conductor(s) around only a portion of the magnetic core with as many turns as necessary, and then assemble the different parts of the magnetic core to obtain the so-called closed magnetic core. Before closing, the smaller cross-sectional parts will be placed along one face of the magnetic core, a face which, after closing, will form one face of the central cavity.

[0036] On the other hand, by implementing a magnetic core without an air gap, that is to say manufactured in a single piece in the form of a closed ring, it is possible to make the filter by winding a wire of constant cross-section around the magnetic core and then enlarging the cross-section of parts of the wire outside the central recess to form the parts with a large cross-section.

[0037] Figures 5 to 7 show several examples of electrical conductors particularly suited to magnetic cores without air gaps. However, it is possible to implement these examples of electrical conductors with assembled magnetic cores.

[0038] Figure 5 shows an electrical conductor 40 formed from an electrical wire 42 of constant cross-section extending across the figure along an axis 44 similar to axis 20. As in Figure 2, axis 44 is straight. 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.

[0039] The electrical conductor 40 comprises, in addition to the electrical wire 42, several sleeves 46 made of electrically conductive material. The sleeves have a shape a tubular section extending along axis 44, the inner face of which is fitted to the outer face of the electrical wire. The electrical wire 42 and the sleeves 46 may have circular cross-sections perpendicular to axis 46. The outer diameter of the sleeves can then form the diameter D of the parts 16b shown in [Fig. 2]. Between the sleeves 46, the electrical wire remains bare to form the parts 16a shown in [Fig. 2].

[0040] Installing an electrical conductor 40 in an inductive filter with a magnetic core without an air gap can be easily accomplished by placing the electrical wire 42 in the central recess and then sliding two sleeves 46 onto the electrical wire 42 on either side of the central recess. If the inductive filter has several turns, a sleeve 46 is slipped onto the electrical wire 42 after each passage of the wire through the central recess. After sliding a sleeve 46 onto the electrical wire, it is possible to secure the sleeve to the wire, for example, by brazing it.

[0041] Before installing an electrically conductive sleeve 42, the electrical wire, in its section 16a, can be covered with another insulating sleeve to prevent any electrical contact between the different sections 16a if the filter comprises several turns, or to prevent any electrical contact between a section 16a and the magnetic core. Similarly, the conductive sleeves 42 can also be covered with insulating sleeves.

[0042] Figures 6 and 7 represent electrical conductors, respectively 50 and 60, in which the parts 16b are formed by sections 52 of electrical wire 52 attached to an electrical wire 42. The electrical conductor 50 shown in [Fig. 6] comprises one section 52 per part 16b, and the electrical conductor 60 shown in [Fig. 7] comprises several sections 52 per part 16b. As with the electrical conductor 40 shown in [Fig. 5], for an implementation with an air-gap-free magnetic circuit, for each part 16b, it is possible to attach 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 parts 16a and 16b, or a single insulating sleeve covering the entire electrical conductor, or one insulating sleeve per part.

[0043] Figure 8 shows a strip that can be wound around an electrical wire to form an electrical conductor suitable for air-gap-free magnetic cores that can be used in an inductive filter according to the invention. To form a part 16b, the strip 70 can be wound around an electrical wire 42. The strip 70 can be wound in several turns around the electrical wire 42. The turns can completely overlap until an outside diameter is reached of the desired part 16b. The width 1 of the strap is then equal to the length L of part 16b, a length defined along axis 44. Alternatively, it is possible to provide a partial overlap of each layer of strap in order to obtain a length L of part 16b greater than the width 1 of the strap 70.

Claims

Claims

1. 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) passing through the central recess (14), the electrical conductor (16) extending along a curved main axis (20; 44) suitable for 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 perpendicular to the main axis in the portion in question and a section of the second portion (16b) is defined perpendicular to the main axis in the portion in question, and wherein a surface area of the first section is less than a surface area of the second section.

2. Inductive filtering device according to claim 1, 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), 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).

3. Inductive filtering device according to one of claims 1 or 2, in which the electrical conductor (40) comprises an electrical wire (42) of constant section along its main axis (44) and an electrically conductive sleeve (46) fitted onto the electrical wire (42) to form the second part (16b).

4. Inductive filtering device according to one of claims 1 or 2, in which the electrical conductor (40) comprises a first electrical wire (42) of constant section along its main axis (44) and 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 one of claims 1 or 2, in which the electrical conductor (40) comprises an electrical wire (42) of constant section along its main axis (44) and a strip (70) wound around the electrical wire (42).

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