Variable impedance differential mode filter

Abstract

Figure for the abstract: 1 The invention relates to a differential mode filter comprising a variable inductor, the variable inductor comprising a primary winding (101) coupled to a secondary winding (102), the secondary winding comprising a switch (103) mounted in series, configured such that: when the switch is in the closed position, the variable inductor has a first inductance value, and when the switch is in the open position, the variable inductor has a second inductance value. The first inductance value is less than the second inductance value.

Description

Title of the invention: Variable impedance differential mode filter Domain

[0001] The present invention relates to a variable impedance differential mode filter, and more particularly to a differential mode filter comprising an inductor with an active circuit allowing its inductance to be changed. Context

[0002] The design of critical applications, for example aircraft electrical networks, must ensure that the network remains stable under all operating conditions. In the context of stability analyses, one of the most widely used criteria (because it is robust for critical applications) is the Middlebrook criterion.

[0003] Such electrical networks typically comprise at least two cascaded converters. Differential mode filters are used at the input and output of these converters to ensure, in particular, the filtering of harmonics related to the switching frequencies. The most commonly used topology is the LC filter, with or without damping, specifically three main differential filter configurations with damping (parallel RC, parallel RL, and series RL).

[0004] However, when the cascaded converters are bidirectional, the stability guaranteed by the Middlebrook criterion can no longer be demonstrated with traditional filters. Since the output impedance of the upstream equipment must be lower than the input impedance of the downstream equipment, when the direction of the power flow changes, the equipment that was a load becomes a source (and vice versa), and this requirement on the respective impedance values ​​is no longer met. Without modification of the impedance profiles according to the mode of operation (load or source), stability in the case of cascaded bidirectional converters can no longer be demonstrated according to the Middlebrook criterion.

[0005] The techniques mentioned in this section should not be presumed to belong to the prior art simply by virtue of their mention. Similarly, a problem mentioned in this same section should not be presumed to have been previously identified in the prior art simply by virtue of its mention. Summary

[0006] Embodiments of the present invention have been developed based on the developers' understanding of the shortcomings associated with the prior art. The invention generally proposes a differential mode filter that varies Its impedance, for example, depends on the operating mode of the equipment (e.g., a converter) with which it is used, whether it is a "source" or "load" filter. The differential mode filter according to the invention comprises an inductor with an active circuit that allows its inductance to be changed.

[0007] More particularly, the present invention comprises, in various embodiments, a differential mode filter comprising a variable inductance, the variable inductance comprising a primary winding coupled to a secondary winding, the secondary winding comprising a series-mounted switch, configured such that: - when the switch is in the closed position, the variable inductance has a first inductance value, and when the switch is in the open position, the variable inductance has a second inductance value; and - the first inductance value is less than the second inductance value.

[0008] In one embodiment of the filter, the secondary winding further includes a first additional impedance in series with the switch.

[0009] In another embodiment of the filter, the secondary winding further comprises a second additional impedance in parallel with the switch and the first additional impedance.

[0010] In another embodiment of the filter, the switch is bidirectional.

[0011] In another embodiment of the filter, the switch is of the electronic type.

[0012] The present invention also comprises, in various embodiments, an electrical network including two bidirectional converters, a first and a second, connected in cascade, the first and second bidirectional converters being electrically connected to respectively a first and a second differential mode filter as above, the first differential mode filter being electrically connected to the second differential mode filter, a first and second switch of respectively the first and second differential mode filters being configured such that: - when the first bidirectional converter is in source mode, and the second converter is in load mode: the first switch is closed, and the second switch is open; and - when the second converter is in source mode, and the first converter is in load mode: the second switch is closed, and the first switch is open.

[0013] The present invention also includes, in various embodiments, an aircraft comprising the above electrical network.

[0014] In the context of this description, unless expressly stated otherwise, the words "first", "second", "third", etc. have been used as adjectives only in the their sole purpose is to allow the names they accompany to be distinguished from one another, and not to describe a particular relationship between these names.

[0015] The implementations of the present invention each have at least one of the objects and / or aspects mentioned above, but do not necessarily have all of them.

[0016] Additional and / or alternative features, aspects and advantages of implementations of the present invention will become apparent from the following description, the accompanying drawings and the attached claims. Brief description of the drawings

[0017] For a better understanding of the present invention, reference is made to the following description which should be used in conjunction with the accompanying drawings, where: [Fig.1] represents an inductance diagram with active circuit in an embodiment of the invention; [Fig.2] represents an inductance modeling scheme with secondary winding equivalent to a transformer; [Fig.3] represents Bode diagrams associated with an inductance simulation in one embodiment of the invention; [Fig. 4] represents inductance diagrams with an active circuit in other embodiments of the invention; and [Fig.5] represents an aircraft including an example of an electrical network implementation implementing the invention. It should be noted that, unless explicitly stated otherwise, the drawings are not to scale. Finally, identical elements from one drawing to another carry the same numerical reference. Description of the implementation methods

[0018] The examples and associated conditions detailed herein are primarily intended to help the reader understand the principles of the present invention and not to limit its scope to these specific examples and conditions. It will be understood that a person skilled in the art can conceive of various arrangements which, although not explicitly described or illustrated herein, nevertheless embody the principles of the present invention and are included in its spirit and scope.

[0019] Furthermore, to facilitate understanding, the following description may describe relatively simplified implementations of the present invention. As a person skilled in the art will understand, other implementations of the present invention may be of greater complexity.

[0020] In some cases, examples of modifications to the present invention may also be presented. This is done simply as an aid to understanding, and, again, not to define the scope or establish the limits of the present invention. These modifications are not an exhaustive list, and a person skilled in the art may make other modifications while remaining within the scope of the present invention.

[0021] Furthermore, all the following statements relating to the principles, aspects, and implementations of the present invention, as well as the specific examples thereof, are intended to encompass both the structural and functional equivalents thereof, whether currently known or developed in the future. Thus, for example, it will be understood by those skilled in the art that all the functional diagrams represent conceptual views of example circuits incorporating the principles of the present invention.

[0022] Having established this, we will now consider some non-limiting examples to illustrate various implementations of the present invention.

[0023] Fig. 1 represents an inductance diagram with active circuit 100 in one embodiment of the invention. This inductance can notably be used in LC type differential mode filters, mentioned in the introduction. It comprises a primary winding 101 coupled to a secondary winding 102. A switch 103 allows, in the closed position, to create a short circuit on the secondary winding 102.

[0024] This inductance with secondary winding 102 is equivalent to a transformer which can be modeled as in [Fig.2]. In this model, inductances 202i and 2022 correspond respectively to the primary winding 101 and the secondary winding 102, of given respective values, and are the dispersion inductances due to the part of the magnetic flux which does not close through the magnetic circuit. A 203 inductance is the magnetizing inductance of the transformer, which normally has a high value due to the significant magnetic permeability of the transformer core, but which can be controlled by the introduction of an air gap (or equivalently, by the use of iron powder magnetic materials with distributed air gap). Resistors 2011 and 2012, corresponding respectively to the primary winding 101 and the secondary winding 102, and a transformer 204, considered as an ideal transformer, complete this model. Current flows between points 205 and 206 of the equivalent of the primary winding 101. Only the alternating components of this current are transmitted to the equivalent of the secondary winding 102.

[0025] When switch 103 is open, the equivalent inductance in the filter's power path is equal to the sum of the primary dispersion inductance 202 and the transformer magnetization inductance 203. The sum of these inductances can be set by design to have the total inductance required for differential filtering when the equipment is operating as a load. If the resistance and inductance values ​​are respectively: - resistance 2011 of the primary winding 101 = Rd - dispersion inductance 202i of the primary winding 101 = Lieaki - magnetization inductance 203 of the primary winding 101 = Lm then the resulting cutoff frequency (in Hz) by the component in this state is obtained by Equation 1: fcut Es1 / 2 TT X (Lm + Lieau)

[0026] When the switch 103 is closed, the secondary winding will create a lower impedance path for the AC components of the current. If the value of the magnetizing inductance 203 is considerably higher (on the order of 10 times) than that of the dispersion inductance 2022 of the secondary, the equivalent inductance of the power path for the AC components can be approximated by the sum of the dispersion inductances 202i and 2022 of the primary and secondary windings, respectively. This sum can be set by design to have a very low value, required for differential filtering when the equipment operates as a source. If the resistance and inductance values ​​are respectively: - resistance 2012 of the secondary winding 102 = Rs2 - dispersion inductance 2022 of the secondary winding 102 = Lieak2 then the resulting cutoff frequency (in Hz) for the component in this state is obtained by Equation 2: fcut (Rsi + Rs2) / 2ir x (Lieaki + Lieak2)

[0027] To demonstrate the effectiveness of the solution of the invention, a simulation diagram obtained using the LTSpice™ tool is presented. The parameter values ​​considered are, for example: Rd = RS2 = 5 m0 hms, Lieak = Lieak2 = 5 µH, Lm = 1000 µH The results are shown by the Bode plots in [Fig.3]. Curves 301a and 301b represent the magnitude and phase, respectively, when switch 103 is in the open state. Curves 302a and 302b represent the magnitude and phase, respectively, when switch 103 is in the closed state.

[0028] The slope of the curves of magnitude 301a and 302a after the characteristic cutoff frequencies of the two systems is 20 dB / dec, which corresponds to an inductive response as expected. The cutoff frequencies have been identified by arrows 301c and 302c on phase curves 301b and 302b, corresponding to frequencies that cross the phase by 45°. Thus, the cutoff frequency calculated by Equation 1 above is 0.792 Hz, which is close to the 301c value of 0.794 Hz resulting from the simulation. Similarly, the cutoff frequency calculated by Equation 2 above is 159.1 Hz, which is close to the 302c value of 158.9 Hz resulting from the simulation. This analysis demonstrates the effectiveness of the proposed solution.

[0029] Examples of variants 400a and 400b of the inductance scheme with active circuit in other embodiments of the invention are shown [Fig. 4]. These inductors also include the primary winding 101 coupled to the secondary winding 102, while the switch 103, in the closed position, creates a short circuit on the secondary winding 102. Compared to the inductance scheme of [Fig. 1], variant 400a includes an additional impedance 401a in series with the switch 103 in the secondary winding 102 circuit. Compared to variant 400a, variant 400b also includes an impedance 401b in series with the switch 103, and an additional impedance 402 in parallel. All these variants can be analyzed by a person skilled in the art, in the same way as the above analysis relating to the inductance scheme of [Fig.1]. Regardless of the variant, the invention allows the use of the same magnetic materials (ferrite, iron powder, nanocrystalline, amorphous), core geometries, and technologies used for conventional differential mode filters.

[0030] Where very low dispersion impedances are required, a high coupling factor between the primary and secondary windings is necessary. In this case, interleaved coil or coaxial wire technologies may be preferable.

[0031] The turns ratio between the primary and secondary windings can be chosen according to the alternating current and voltage levels in the frequency domain. A high turns ratio allows for a lower number of turns in the secondary winding and a lower voltage, thus enabling the use of a lower voltage capacitance switch. However, the current obtained in the secondary winding will be higher.

[0032] The switch 103 used in the secondary winding is advantageously bidirectional, since the current flowing is alternating. For reasons of speed, the use of electronic switches is preferable, based on semiconductors (for example, of the type: insulated-gate field-effect transistor, modulated-doped field-effect transistor, or bipolar junction transistor, respectively: MOSFET, HEMT, BJT in English). Depending on the ratio of turns, it is preferable to use components with a low voltage drop in the closed state (or equivalently, a low resistance in the on state), so that the device does not add more elements in series to the system.

[0033] The invention thus makes it possible, in particular, to dynamically (i.e., during operation) modify the impedance of differential-mode filters associated with bidirectional converters, depending on whether the converters are operating as a source or as a load. This is necessary to demonstrate the stability of critical electrical networks using the Middlebrook criterion, a criterion currently used in network analysis for critical applications.

[0034] The aircraft 500 shown in [Fig. 5] includes an example of an electrical network implementation 501 implementing the invention. The electrical network comprises at least two bidirectional converters, a first and a second, connected in cascade. These bidirectional converters can be, alternately, the source and the load with respect to each other. Each of the bidirectional converters is equipped, at its input and output, with a differential mode filter according to the invention. Actuating the respective switches of these different differential mode filters ensures that the output impedance of the source bidirectional converter is lower than the input impedance of the load bidirectional converter.Thus, if the first of the two bidirectional converters is in source mode (i.e., the second is in load mode), the switch on its associated output differential mode filter will be closed, while the switch on the input differential mode filter of the second converter will also be closed. When the second of the two bidirectional converters is in source mode (i.e., the first is in load mode), the switch on its associated output differential mode filter will be closed, while the switch on the input differential mode filter of the first converter will also be closed.

[0035] Modifications and improvements to the above-described implementations of the present invention may be apparent to a person skilled in the art. The above description is illustrative by way of examples rather than exhaustive. The scope of the present invention is therefore limited only by the scope of the claims below.

Claims

Demands

1. Differential mode filter comprising a variable inductance, the variable inductance comprising a primary winding (101) coupled to a secondary winding (102), the secondary winding comprising a switch (103) mounted in series, configured such that: - when the switch is in the closed position, the variable inductance has a first inductance value, and when the switch is in the open position, the variable inductance has a second inductance value; and - the first inductance value is less than the second inductance value.

2. Differential mode filter of claim 1, wherein the secondary winding further comprises an additional first impedance (401a) in series with the switch (103).

3. Differential mode filter of claim 2, wherein the secondary winding further comprises a second additional impedance (402) in parallel with the switch (103) and the first additional impedance (401b).

4. Differential mode filter according to any one of claims 1 to 3, wherein the switch is bidirectional.

5. Differential mode filter according to any one of claims 1 to 3, wherein the switch is of the electronic type.

6. Electrical network (501) comprising two bidirectional converters, a first and a second, connected in cascade, the first and second bidirectional converters being electrically connected to, respectively, a first and a second differential mode filter according to any one of claims 1 to 5, the first differential mode filter being electrically connected to the second differential mode filter, a first and second switch of, respectively, the first and second differential mode filters being configured such that: - when the first bidirectional converter is in source mode, and the second converter is in load mode: the first switch is closed, and the second switch is open; and

7. - when the second converter is in source mode, and the first converter is in load mode: the second switch is closed, and the first switch is open. Aircraft (500) comprising the electrical network (501) of claim 6.

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