ELECTROMAGNETIC FILTERING OF A CONTROL CIRCUIT OF AN ELECTRIC MOTOR

Abstract

The invention relates to a control circuit (1) of an electric motor (4), the control circuit (1) comprising a filtering device (13) in order to filter the high frequencies likely to produce perturbing electromagnetic radiation when the electric motor (4) is driven. To this end, the filtering device (13) comprises a first filtering device (131) branched off from a power bridge (12) driving the electric motor (4), each filtering branch forming the first filtering device (131) being located near the power bridge (12) and/or one of the corresponding power branches (A, B, C) of said power bridge (12) so that a length of an electrical conductor (1313) connecting said filtering branch to said power branch is less than 20 mm. The invention also relates to a motorized-fan unit (8) for motor vehicles comprising such a control circuit (1).

Claims

1. A control circuit of an electric motor, the control circuit comprising: a power bridge comprising at least one power branch, the power bridge being configured to drive the electric motor; and a first filtering device comprising at least one filtering branch arranged in parallel with the power bridge via two connection terminals, in order to filter electromagnetic radiation from said power bridge, wherein at least one of the connection terminals of the first filtering device is located near a connection point of the power bridge, so that a length of an electrical conductor connecting said connection terminal of the first filtering device to the connection point of the power bridge is less than or equal to 20 mm.

2. The control circuit as claimed in claim 1, wherein each connection terminal of the first filtering device is located near a connection point of the power bridge, so that a length of the electrical conductor connecting each connection terminal of the first filtering device to the corresponding connection point of the power bridge is less than or equal to 20 mm.

3. The control circuit as claimed in claim 1, wherein the first filtering device comprises a number of filtering branches equal to a number of power branches of the power bridge, each filtering branch being associated with a single power branch, so that a length of the electrical conductor connecting the connection terminal of each filtering branch to the corresponding connection point of the power branch is less than or equal to 20 mm.

4. The control circuit as claimed in claim 1, wherein the first filtering device is of the type of a low-pass filter, a cutoff frequency of which is between 800 kHz and 1.2 MHz.

5. The control circuit as claimed in claim 1, wherein each filtering branch of the first filtering device comprises a filtering capacitor, a capacitance value of the filtering capacitor being greater than 1 mF.

6. The control circuit as claimed in claim 1, wherein the control circuit comprises a second filtering circuit comprising at least one filtering branch arranged in parallel with the power bridge via two connection terminals.

7. The control circuit as claimed in claim 6, wherein a cutoff frequency of the second filtering circuit is greater than a cutoff frequency of the first filtering circuit.

8. The control circuit as claimed in claim 6, wherein the second filtering device comprises a number of filtering branches equal to a number of power branches of the power bridge, each filtering branch being associated with a single power branch, so that a length of the electrical connector connecting the connection terminal of each filtering branch to the corresponding connection point of the power branch is less than or equal to 20 mm.

9. The control circuit as claimed in claim 6, wherein the second filtering device is of the type of a low-pass filter, a cutoff frequency of which is greater than 100 MHz, each filtering branch of the second filtering device comprising a filtering capacitor, a capacitance value of which is less than 1 μF.

10. The control circuit as claimed in claim 9, in which the filtering capacitor of each filtering branch of the second filtering device is of the type of a capacitive film or a ceramic capacitor.

11. A motorized-fan unit for motor vehicles, said motorized-fan unit comprising: a fan rotated by an electric motor; and a control circuit configured to drive the electric motor, the control circuit comprising: a power bridge comprising at least one power branch, the power bridge being configured to drive the electric motor; and a first filtering device comprising at least one filtering branch arranged in parallel with the power bridge via two connection terminals to filter electromagnetic radiation from said power bridge, wherein at least one of the connection terminals of the first filtering device is located near a connection point of the power bridge, so that a length of an electrical conductor connecting said connection terminal of the first filtering device to the connection point of the power bridge is less than or equal to 20 mm.

Description

DESCRIPTION OF THE FIGURES

[0035] Further features and advantages of the invention will become apparent from the following description and from several exemplary embodiments given as non-limiting examples with reference to the attached schematic drawings, in which:

[0036] FIG. 1 illustrates a circuit diagram of an electric motor driven by a control circuit in accordance with the first aspect of the invention;

[0037] FIG. 2 illustrates a first exemplary embodiment of such a control circuit in accordance with the first aspect of the invention;

[0038] FIG. 3 illustrates a second exemplary embodiment of such a control circuit in accordance with the first aspect of the invention.

[0039] Of course, the features, variants and different embodiments of the invention can be combined with one another, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention can be envisaged that comprise only a selection of the features described below in isolation from the other features described, if this selection of features is sufficient to provide a technical advantage or to distinguish the invention from the prior art.

[0040] In particular, all of the variants and all of the embodiments described can be combined with each other if there is no technical reason preventing this combination.

[0041] In the figures, elements common to a number of figures keep the same reference.

DETAILED DESCRIPTION OF THE INVENTION

[0042] FIG. 1 illustrates an electrical system intended to be installed for example in a motor vehicle, not shown, and an electric power for which—represented by a voltage U.sub.bat—is provided by a battery 2 via a vehicle electrical system 21. In the example illustrated in FIG. 1, such an electrical system forms a motorized-fan unit 8 in accordance with the third aspect of the invention.

[0043] Such a motorized-fan unit 8 comprises an electric motor 4 driven by a control circuit 1, a rotor of the electric motor 4 being mechanically coupled to a shaft 52 rotating a propeller 51 of a fan 5. The control circuit 1 is in accordance with the first aspect of the invention and will be described later on with reference to FIGS. 2 and 3.

[0044] The electric motor 4 driven by the control circuit 1 can be of any type, and in particular of the type of a DC motor, for example, preferably polyphase and driven by a power bridge. The electric motor 4 comprises an armature element 41 and an inductor element 42. In the example illustrated in FIG. 1, the armature element 41 is a rotor of the electric motor 4; and the inductor element 42 is a stator of said electric motor 4. Advantageously, the inductor element 42 comprises a number N of electrical windings 421. In the example illustrated in FIG. 1, N is equal to 3. According to a particular embodiment of the invention, the electrical windings 421 of the inductor element 42 are arranged in a so-called “star” electrical configuration, all the electrical windings 421 being electrically connected to one another at a common electrical terminal. Alternatively, other electrical configurations can be envisaged, such as for example a delta or ring configuration.

[0045] According to another variant of the invention, the electric motor 4 is of the brushless type, the rotor of the electric motor 4 comprising one or more permanent magnets forming the armature element 41, and the electrical windings 421 of the stator then form the inductor element 42 of the electric motor 4.

[0046] The electric motor 4 is driven by a control circuit 1 that allows selective or collective production of the phase currents i.sub.A, i.sub.B, i.sub.C of each of the electrical windings 421 of the inductor element 42 of said electric motor 4. The control circuit 1 is itself driven by a control module 3 that generates one or more control signals sc for the control circuit 1, as will be described in more detail with reference to FIGS. 2 and 3. In addition, the control module 3 is also configured to determine an induced current i.sub.rot at the armature element 41 of the electric motor 4.

[0047] The control circuit 1 is branched off from the battery 2 of the motor vehicle, between a positive terminal and a ground terminal M, through the vehicle electrical system 21. The ground terminal M is advantageously electrically connected to a chassis of the motor vehicle for reasons of electrical safety.

[0048] With reference to FIG. 2, two exemplary embodiments of a control circuit 1 in accordance with the first aspect of the invention are described, each control circuit 1 comprising a power bridge 12 and a filtering device 13.

[0049] The power bridge 12 comprises at least one power branch A, B, C, in order to produce at least one phase current i.sub.A, i.sub.B, i.sub.C for each of the electrical windings 421 of the inductor element 42 of said electric motor 4. All the power branches A, B, C are firstly branched off from one another, and polarized by the voltage U.sub.bat delivered by the battery 2 of the motor vehicle. In the examples illustrated in FIGS. 2 and 3, in correspondence with the motorized-fan unit 8 illustrated in FIG. 1, the power bridge 12 comprises three power branches A, B, C, each of the power branches A, B, C being associated with one of the electrical windings 421.

[0050] Each power branch A, B, C comprises two power switches 121. Each power switch 121 is configured to produce the corresponding phase current i.sub.A, i.sub.B, i.sub.C. The phase current i.sub.A, i.sub.B, i.sub.C produced by the power switches of each branch A, B, C of the control circuit 1 is of the type of a pulse-width modulation signal in order to control the rotation and/or the speed of rotation of the electric motor 4. For this purpose, each power switch 121 is alternately configured in an on conduction state—in which it has a very low resistance between its terminals—and in an off conduction state—in which it has a very high resistance between its terminals. The toggling of the power switches 121 between their on and off conduction states is driven by the control module 3 and allows the characteristics of the corresponding phase currents i.sub.A, i.sub.B, i.sub.C, such as for example a frequency and/or a duty cycle, to be controlled.

[0051] Each power switch 121 is advantageously of the type of a power transistor, such as for example a MOS, a MOSFET, preferably N doped as in the examples illustrated in FIGS. 2 and 3.

[0052] For each power branch A, B, C, the two power switches 121 are advantageously electrically connected at a common terminal, for example via a drain terminal of a first power transistor and via a source terminal of a second power transistor of the same power branch A, B, C. Subsequently, the terminal common to the two power components 121 is then electrically connected to one of the electrical windings 421 of the electric motor 4 in order to control an electric current flowing through it.

[0053] According to the first aspect of the invention, in order to filter electromagnetic radiation from the power bridge 12 during operation thereof, the filtering device 13 comprises a first filtering device 131. For this purpose, the first filtering device 131 comprises three filtering branches each comprising a filtering capacitor 131A, 131B, 131C, respectively. As can be seen in FIGS. 2 and 3, each filtering branch of the first filtering device 131 is firstly branched off from the power bridge 12 and secondly placed in parallel with the voltage U.sub.bat delivered by the battery 2 of the motor vehicle.

[0054] More particularly, each filtering branch of the first filtering device 131 is associated with one of the power branches A, B, C of the power bridge 12. In other words, each filtering branch of the first filtering device 131 is branched off from one of the power branches A, B, C of the power bridge 12, so that each of the filtering capacitors 131A, 131B, 131C of the first filtering device 131 is branched off from the power switches 121, 122 forming one of said power branches A, B, C.

[0055] In line with the invention according to its first aspect, one of the connection terminals 1311, 1312 of the first filtering device 131 is located near a connection point 1211A, 1221A, 1211B, 1221B, 1211C, 1221C of the power bridge 12, so that a length of an electrical conductor 1313 connecting said connection terminal 1311, 1312 of the first filtering device 131 to the connection point 1211A-1211C, 1221A-1221C of the power bridge 12 is less than or equal to 20 mm.

[0056] As can be seen in FIGS. 2 and 3, each connection terminal 1311, 1312 of the first filtering device 131 is located near the corresponding connection point 1211A-1211C, 1221A-1221C of the power bridge 12, so that the length of an electrical conductor 1313 is less than or equal to 20 mm.

[0057] A length of 20 millimeters is in fact a maximum value beyond which the antenna effects become too great for the technical problem of the present invention.

[0058] The first filtering device 131 is advantageously of the type of a low-pass filter, a cutoff frequency of which is between 800 kHz and 1.2 MHz, a value of the filtering capacitors 131A-131C of said first filtering device 131 being greater than 1 mF, and preferably equal to 2700 μF.

[0059] Additionally, in the exemplary embodiments illustrated in FIGS. 2 and 3, the filtering device 13 of the control circuit 1 also comprises a second filtering circuit 132. The second filtering device 132, which is optional for solving the technical problem, allows the performance of the filtering device 13 to be improved by offering a cutoff frequency that is different than that of the first filtering device. For this purpose, the second filtering device 132 is advantageously of the type of a low-pass filter, a cutoff frequency of which is greater than that of the first filtering device 131, for example greater than 100 MHz.

[0060] The second filtering device 132 comprises one or more filtering branches that are firstly branched off from the power bridge 12 and secondly arranged in parallel with the voltage U.sub.bat delivered by the battery 2 of the motor vehicle.

[0061] According to a first exemplary embodiment illustrated in FIG. 2, each filtering branch of the second filtering device 132 is associated with one of the power branches A, B, C of the power bridge 12. In other words, each filtering branch of the second filtering device 132 is branched off from one of the power branches A, B, C of the power bridge 12, so that each of the filtering capacitors 132A, 132B, 132C of the second filtering device 132 is branched off from the power switches 121, 122 forming one of said power branches A, B, C.

[0062] In this first exemplary embodiment, one of the connection terminals 1321, 1322 of the second filtering device 132 is located near one of the connection terminals 1211A-1211C, 1221A-1221C of the power bridge 12, so that a length of an electrical connector 1323 connecting said connection terminal 1321, 1322 of said second filtering device 132 to the connection point 1211A-1211C, 1221A-1221C of the power bridge 12 is less than or equal to 20 mm.

[0063] As can be seen in FIG. 2, each connection terminal 1321, 1322 of the second filtering device 132 is located near the corresponding connection point 1211A-1211C, 1221A-1221C of the power bridge 12, so that the length of the corresponding electrical connector 1323 is less than or equal to 20 mm.

[0064] A length of 20 millimeters is in fact a maximum value beyond which the antenna effects become too great for the technical problem of the present invention.

[0065] According to a second exemplary embodiment illustrated in FIG. 3, the filtering branches of the second filtering device 132 are grouped together in front of the power bridge 12, the three power branches of said second filtering device 132 all being branched off from the power bridge 12.

[0066] In the first or the second exemplary embodiment, each filtering branch of the second filtering device 132 comprises a filtering capacitor 132A-132C. A capacitance value of each filtering capacitor 132A-132C of the second filtering device 132 is advantageously less than 1 μF, and preferably between 100 nF and 300 nF.

[0067] Optionally, in the second exemplary embodiment illustrated in FIG. 3, all the filtering capacitors 132A-132C of the second filtering device 132 can be grouped together as a single equivalent filtering capacitor branched off from the power bridge 12.

[0068] In summary, the invention relates to a control circuit 1 of an electric motor 4, the control circuit 1 comprising a filtering device 13 in order to filter the high frequencies likely to produce perturbing electromagnetic radiation when the electric motor 4 is driven. To this end, the filtering device 13 comprises a first filtering device 131 branched off from a power bridge 12 driving the electric motor 4, each filtering branch forming the first filtering device 131 being located near the power bridge 12 and/or one of the corresponding power branches A, B, C of said power bridge 12 so that a length of an electrical conductor 1313 connecting said filtering branch to said power branch is less than 20 mm.

[0069] Of course, the invention is not limited to the examples that have just been described, and numerous modifications can be made to these examples without departing from the scope of the invention. In particular, the various features, forms, variants and embodiments of the invention can be associated with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, all of the variants and embodiments described above can be combined with each other.