DC VOLTAGE FILTER FOR AN INPUT OF AN INVERTER OF AN ELECTRIC MACHINE FOR PROPELLING AN AIRCRAFT

A filter includes a positive busbar and a negative busbar that have a positive terminal and a negative terminal, respectively; at least one positive output terminal and at least one negative output terminal, respectively; and two portions, respectively, each portion having parallel folds to define planes which succeed one another. Each plane is inclined relative to the next plane. One of the portions is an internal portion that is fitted inside the other portion, which is an external portion. Each plane of one portion extends in parallel with and facing an associated plane of the other portion. Differential mode capacitors connected between the two portions.

SUMMARY OF THE INVENTION

A DC voltage filter is therefore proposed for an inverter input of an electric machine for propelling an aircraft, comprising:a positive busbar and a negative busbar, respectively having two portions each having substantially parallel folds so as to define at least three planes following one another and inclined with respect to one another, one of the portions, referred to as internal, being nested in the other, referred to as external, so that each plane of one extends substantially parallel opposite an associated plane of the other; anddifferential mode capacitors connected between the two portions.

Optionally, the positive busbar and the negative busbar comprise a positive input terminal and a negative input terminal respectively, and/or at least one positive output terminal and at least one negative output terminal respectively. Capacitive input filters are generally provided between global input terminals and the input terminals of the busbars. To avoid a confusion with the global input terminals, the input terminals of the busbars are referred to hereafter as “intermediate”.

Optionally, more differential mode capacitors are connected between the central pair or pairs of planes than between the two peripheral pairs of planes.

Optionally, the differential mode capacitors are arranged on an external face of the external portion and/or on an internal face of the internal portion.

Also proposed is a voltage converter comprising:at least one power module; anda filter according to the invention, each power module being connected to a respective pair of positive and negative output terminals.

An electric drive is also proposed, comprising:a voltage converter according to the invention;an electric motor;an output shaft secured to a rotor of the electric motor, the input filter being arranged around the output shaft so that the portions of the busbars surround the output shaft.

Optionally, several voltage converters are distributed around the output shaft.

Also optionally, the electric drive further comprises a casing surrounding the output shaft and having a plurality of internal or external planar faces in succession around the output shaft, the input filter being pressed against the planar faces of the casing so that each plane of the lower portion extends substantially parallel opposite an associated planar face of the casing.

An aircraft comprising an electric drive according to the invention is also proposed.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIG.1, an example of an electric drive100for an aircraft will now be described.

The electric drive100firstly comprises a DC voltage source102designed to supply a DC voltage U. The DC voltage source102comprises, for example, one or more batteries.

The electric drive100also comprises at least one inverter1041-3connected by a DC power harness105to the DC voltage source102and each designed to convert the DC voltage U into a respective AC voltage V1-3. Each AC voltage V1-3is, for example, a polyphase voltage, in particular a three-phase voltage.

Each inverter1041-3comprises in particular an input filter1061-3and, for each input filter, one or more power modules, each designated by the global reference1081-3and designed to respectively supply the different phase or phases of the AC voltage V1-3from the DC voltage U after filtering by the input filter1061-3. If the AC voltage V1-3is three-phase, for example, three power modules1081-3are provided.

Each inverter104also comprises control electronics1101-3designed to control the power modules1081-3.

Using several inverters104in parallel allows to reduce the electrical power passing through each of them.

The electric drive100also comprises an electric motor112with a stator and a rotor (not shown). The electric motor112is, for example, a permanent magnet synchronous motor.

The stator has stator windings (not shown) electrically connected to the power modules1081-3by a polyphase power harness113to receive the phases of the AC voltages V1-3respectively. In response to the AC voltages V1-3, the stator is designed to generate a rotating magnetic field.

The rotor, for example with a permanent magnet, is designed to be driven in rotation by the rotating magnetic field, in order to drive, for example, a propeller114of the electric drive100, to which the rotor is mechanically connected via an output shaft116of the electric drive100.

Preferably, as shown inFIG.1, a second electrical supply path is provided with elements similar to those of the first path. These similar elements carry the same reference numbers as those in the first path, with the addition of an asterisk “*”.

The two paths are preferably independent of each other so that a fault on one path does not cause a fault on the other. In this way, in the event of the loss of a complete path, a minimum supply via the other path can be guaranteed. In particular, this second path preferably comprises a second DC voltage source102* (independent of the first102) and inverters104*1-3.

In the example shown, each path comprises three inverters in parallel, each capable of supplying up to 90 kW of electrical power. The electric motor112is designed to supply 500 kW of mechanical power. To achieve this, each path supplies 250 kW of electrical power (83.3 kW per inverter on that path).

With reference toFIG.2, one of the input filters1061-3,106*1-3will now be described in more detail. InFIGS.2to6it will be designated simply by the reference106, the inverter to which this input filter106belongs will be designated simply by the reference104, and the power modules connected to this filter will be designated simply by the reference108.

The input filter106firstly comprises a positive input terminal HVDC+ and a negative input terminal HVDC− designed to receive the DC voltage U.

The input filter106also comprises two differential mode inductors Ldm+, Ldm− respectively connected to the input terminals HVDC+, HVDC−.

The input filter106also comprises a positive busbar202+ and a negative busbar202−, respectively having a positive intermediate terminal204+ and a negative intermediate terminal204− respectively connected to the differential mode inductors Ldm+, Ldm−.

The differential mode inductors Ldm+, Ldm− have a value that ensures a network stability so that the resonance of the filter106is independent of the cable length (as far as possible). For example, each differential mode inductor Ldm+, Ldm− is between 2 and 3 pH, for example 2.5 pH.

The positive busbar202+ also has at least one positive output terminal P1+, P2+, P3+, in particular one for each power module108.

Similarly, the negative busbar202− has at least one negative output terminal P1−, P2−, P3−, in particular one for each of the power modules108associated with this input filter106.

The busbars202+,202− are rigid electrical conductors, preferably laminated to reduce the switching loop inductor. Reducing the switching loop inductor is important when using power components in order to reduce the losses associated with switching the power modules108and to avoid over-voltages at the electric motor input112.

The input filter106also comprises several differential mode capacitors Cdm connected between the busbars202+,202−. The number of differential mode capacitors Cdm is preferably high, to allow them to be distributed, as will be explained later. Preferably there should be at least ten of them.

These differential mode capacitors Cdm together have a capacitance value chosen so as to reduce the variation in the DC voltage U and to ensure a sufficient network quality to support the currents of the inverter104. For example, the equivalent capacitor is between 100 and 200 ρF. For example, each capacitor has a value of 12.6 μF for a total of 151 μF for twelve differential mode capacitors Cdm in parallel.

The differential mode capacitors Cdm used are preferably polypropylene type capacitors whose service life depends on the voltage level and temperature. In power equipment, the service life is often given by the service life of the capacities used. So, to increase or guarantee a long service life, it is preferable to optimise the cooling of the differential mode capacitors Cdm.

The input filter106also comprises, for each output terminal, a common mode capacitor Cdm connected to the busbar to which that output terminal belongs.

The input filter106also comprises a device for measuring the current in at least one of the busbars202+,202−. In the example described, the current measuring device is designed to measure the current flowing in the negative busbar202− and comprises, for example, a resistor206.

With reference toFIGS.3and4, the busbars202+,202− will now be described in more detail.

The busbars202+,202− respectively comprise two portions302+,302− each having a curved shape, in a single orientation of curvature, and designed to nest into each other so as to extend at a substantially constant distance from each other.

In the example shown, the negative busbar202− comes to nest in the positive busbar202+. The positive busbar202+ will hereinafter be referred to as external, while the negative busbar202− will hereinafter be referred to as internal. Of course, in other embodiments, the negative busbar202− could be external and the positive busbar202+ could be internal.

The curvature ofthe portions302+,302− is obtained by the fact that each portion302+,302− has substantially parallel folds in order to define planes which follow one another and are inclined with respect to one another, the inclination always being in the same orientation (no zigzag). In the example shown, each portion302+,302− comprises three inclined planes304+,306+,308+ and304−,306−,308−.

Once the busbars202+,202− are nested together, each plane of one of the busbars202+,202− extends substantially parallel opposite an associated plane of the other of the busbars202+,202−. More specifically, in the example shown, the planes304+,304− extend opposite each other, as do the planes306+,306− and the planes308+,308−.

The busbars202+,202− are preferably covered with an electrically insulating film402, which is shown transparently inFIG.4.

With reference toFIG.5, the differential mode capacitors Cdm are connected between the two portions302+,302− of the busbars202+,202−. Preferably, the differential mode capacitors Cdm are arranged on an external face of the external busbar and/or on an internal face of the internal busbar. In the example shown, all the differential mode capacitors are arranged on the external face of the positive busbar202+.

In particular, each pair of planes facing the busbars202+,202− carries at least two differential mode capacitors Cdm. Preferably, the central pair of planes (the planes306+,306− in the example shown) carries more differential mode capacitors Cdm than the peripheral pairs of planes (the planes304+,304− and308+,308− in the example described).

Thus, in the example shown, the pair of planes306+,306− carries six differential mode capacitors Cdm, while each of the pairs of planes304+,304− and308+,308− carries three differential mode capacitors Cdm.

In addition, the input filter106preferably comprises a base plate502carrying the bus plates202+,202−. In particular, the base plate502is itself curved to nest into the internal busbar and extend at a substantially constant distance from the latter. In the example shown, the base plate502comprises three planes extending parallel opposite to the planes304+,306+,308+ of the negative busbar202−.

The differential mode inductors Ldm+, Ldm− are, for example, carried by the base plate502. Preferably, a thermal interface is provided between each differential mode inductor Ldm+, Ldm− and the base plate502to optimise the cooling towards the base plate502.

The input filter106may also comprise, carried by the busbars202+,202− and/or by the base plate502, a device504for measuring the voltage U and a connector506for transmitting the voltage measurement.

The input filter106may further comprise a device (not visible) for measuring a temperature of the input filter106, in particular a temperature of one of the differential mode capacitors Cdm and connectors508for transmitting the temperature measurement.

For example, the resistor206used to measure current comprises a current shunt510with two pins512between which a voltage is measured to deduce the current.

All or some of these measurements are sent to the control electronics110of the power modules108, to be used to control the switches of the power modules108. To do this, the control electronics110comprises, for example, a module for processing and digitising the measurements, this processing module receiving the connectors506,508and the pins512.

With reference toFIG.6, an electrically insulating layer602is provided between the internal busbar (the negative busbar202− in the example described) and the base plate502.

The electrical insulating layer602should preferably be able to withstand 1000 V under all altitude and temperature conditions encountered by the aircraft, between the two busbars202+,202− and the base plate502forming an electrical mass.

The input filter106also comprises a housing504which comes into contact with the base plate502and covers the differential mode capacitors Cdm, as well as, for example, the differential mode inductors Ldm and/or the common mode capacitors Ccm. The housing504is for example filled with a thermal insulating material506, such as a resin, so that the heat generated by the differential mode capacitors Cdm and the differential mode inductors Ccm is dissipated towards the busbars202+,202− and then through the base plate502. Thus, thanks to the thermal insulating material506, a direct heat transfer between the differential mode inductors Ldm and the differential mode capacitors Cdm is limited. This is because the differential mode inductors Ldm generally heat up much more than the differential mode capacitors Cdm, and the latter generally cannot withstand very high temperatures. In this way, it is possible to place these components close to each other, and thus achieve a good compactness, without the components that heat a lot raising the temperature of the components that heat less and cannot withstand too high a temperature. For example, the thermal insulating material506has a thermal conductivity of less than 0.5 W/m/K.

In addition, in the event of a problem with a component, the thermal insulating material506is designed to contain an explosion of this component.

With reference toFIGS.7to9, an example of integration of the electric drive100will now be described.

In this example, each power transmission path comprises three inverters1041-3,104*1-3. The electric drive100therefore comprises six input filters1061-3,106*1-3.

The output shaft116(not shown inFIGS.7and8) secured to the rotor of the electric motor112extends along an axis of rotation DD′.

The electric drive100comprises a casing702surrounding the output shaft116and having a number of planar faces, internal704and external706in succession around the output shaft116. Preferably, the internal704and external706faces have the same number and are substantially angularly offset around the axis of rotation DD′ by half a planar face. In the example shown, the casing702has nine internal planar faces704and nine external planar faces.

The input filters1061-3,1061-3* are distributed around the axis of rotation DD′ with their curvature around the axis of rotation DD′. More specifically, in the example shown, the input filters1061-3of the first path are pressed against the external faces706, while the input filters106*1-3of the second path are pressed against the internal faces704. In this way, each input filter1061-3,106*1-3is pressed against planar faces704or706of the casing702so that each base plate502(and therefore each plane of the portion of the lower busbar) extends substantially parallel opposite an associated planar face of the casing702.

In a similar way, the power modules1081-3,1081-3* are for example distributed around the axis of rotation DD′ and placed between the input filters1061-3,1061-3* and the electric motor112. More precisely, each power module1081-3,108*1-3is pressed against an internal704or external706planar face of the casing702, in particular against one of the planar faces on which the input filter1061-3,1061-3* of this power module1081-3,1081-3* is pressed. The angular offset between the internal faces704and the external faces706allows the power modules1081-3,1081-3* to be placed in series one after the other along the same cooling circuit, the latter alternately cooling a power module1081-3* on an internal face704, then that on an external face706, and so on.

The inlet filters1061-3,1061-3* are compactly integrated into a small, rounded volume. In addition, the length of the polyphase harnesses1131-3,1131-3* is very short, which allows to reduce the parasitic inductors between the differential mode capacitors Cdm and the power modules1081-3,108*1-3.

In this way, the heat dissipation towards the casing702is facilitated by the fact that the busbars202+,202− are pressed against the casing702(through the base plate502in the example described) over a large surface area, due to their curved shape which complements that of the casing702.

It should be noted that the invention is not limited to the embodiments described above. In fact, it will appear to the person skilled in the art that various modifications can be made to the above-described embodiments, in the light of the teaching just disclosed.

In particular, the input filter could be purely capacitive and not comprise differential mode inductors.

In the foregoing detailed presentation of the invention, the terms used should not be interpreted as limiting the invention to the embodiments exposed in the present description, but should be interpreted to include all equivalents the anticipation of which is within the reach of the person skilled in the art by applying his general knowledge to the implementation of the teaching just disclosed.