EP3542457A1

EP3542457A1 - Rotating electrical machine with improved efficiency

Info

Publication number: EP3542457A1
Application number: EP17804640.5A
Authority: EP
Inventors: Mamy Rakotovao; Philippe-Siad Farah; Frédéric Palleschi
Original assignee: Valeo Equipements Electriques Moteur SAS
Current assignee: Valeo Equipements Electriques Moteur SAS
Priority date: 2016-11-18
Filing date: 2017-11-17
Publication date: 2019-09-25
Also published as: WO2018091847A1; FR3059168A1; FR3059168B1; CN110063019A

Abstract

The invention mainly relates to a rotating electrical machine (7) arranged to operate at least in motor mode, in particular for an electrical turbocharger (1) of a motor vehicle, comprising: a stator (9) having a winding equipped with a plurality of electrical phases, a rotor (10) with permanent magnets, said rotating electrical machine (7) having a saliency ratio equal to an inductance in a quadrature axis divided by an inductance in a direct axis, an inverter for electrically controlling said rotating electrical machine, characterised in that the rotating electrical machine (7) is configured so that the saliency ratio is greater than 1.2, in particular greater than or equal to 1.5, for example between 1.5 and 3, the inverter being configured to generate a negative current in the direct axis in the electrical phases of the stator (9) in order to reduce the magnetic flux in the direct axis, in such a way as to create a positive reluctance torque.

Description

ROTATING ELECTRICAL MACHINE WITH IMPROVED YIELD

The invention relates to a rotor of rotating electrical machine with improved efficiency.

In known manner, the rotating electrical machines comprise a stator and a rotor secured to a shaft. The rotor may be integral with a driving shaft and / or driven and may belong to a rotating electrical machine in the form of an alternator, an electric motor, or a reversible machine that can operate in both modes.

The stator is mounted in a housing configured to rotate the shaft for example by means of bearings. The stator comprises a body constituted by a stack of thin sheets forming a ring, the inner face of which is provided with notches open towards the inside to receive phase windings. In a distributed corrugated type winding, the windings are obtained for example from a continuous wire coated with enamel or from conductive elements in the form of pins connected together by welding. Alternatively, in a "concentric" type winding, the phase windings are constituted by closed coils on themselves which are wound around the teeth of the stator. These windings are polyphase windings connected in star or delta or star delta whose outputs are connected to a control electronics. The system can be double three-phase.

In addition, the rotor comprises a body formed by a stack of sheets of sheet metal held in pack form by means of a suitable fastening system. The rotor has poles formed by permanent magnets housed in cavities in the rotor body.

Rotating electrical machines are known that are coupled to a shaft of an electric compressor. This electric compressor makes it possible to compensate, at least in part, for the loss of power of the reduced-displacement heat engines used on many motor vehicles in order to reduce their consumption and the emissions of polluting particles (so-called "downsizing" principle in English). For this purpose, the electric turbocharger, arranged on the intake duct upstream of the engine, comprises a turbine to allow air to be compressed in order to optimize the filling of the cylinders of the engine. The electric machine is activated to drive the turbine at a very high speed in order to minimize the torque response time, in particular during the transient phases during acceleration, or in the automatic restart phase of the heat engine after a standby (operation " stop and start ").

It is recalled that the electromagnetic saliency of a rotating electrical machine is defined by the relation that exists between the inductance in the direct axis (Ld) and the inductance in the quadrature axis (Lq). In order to generate an optimal electromagnetic torque, it is known that positive current must be injected into the armature, along the quadrature axis (Q axis) so as to produce a current in quadrature with respect to the magnetic flux generated by the inductor.

In the case of a rotating electric machine with permanent magnets rotating at a high rotational speed, particularly greater than 10,000 revolutions per minute, as is the case for the turbocharger, the magnetic flux generated by the permanent magnets of the rotor along the axis direct (D-axis) creates a counter-electromotive force in the quadrature axis (Q-axis), which prevents effective sending of positive current along the quadrature axis to create the optimum torque.

The present invention aims to effectively remedy this need by providing a rotating electrical machine arranged to operate at least in engine mode, in particular for an electric motor vehicle turbo-compressor, comprising:

a stator comprising a winding provided with a plurality of electrical phases,

a rotor with permanent magnets,

said rotating electrical machine having a saliency coefficient equal to an inductance in a quadrature axis divided by an inductance in a direct axis, an inverter for electrically controlling said rotating electrical machine,

characterized in that

said rotating electrical machine is configured so that the coefficient of salience is greater than 1, 2, in particular greater than or equal to 1, 5, for example between 1, 5 and 3,

- The inverter being configured to generate a negative current in the direct axis in the electric phases of the stator to reduce the magnetic flux in the direct axis, so as to create a positive reluctant torque. The invention thus makes it possible to increase the inductance in the quadrature axis, which makes it possible to increase the magnetic flux in the quadrature axis while reinforcing the torque generated by the electric machine. The invention therefore makes it possible to deflux the electric machine without degrading the efficiency thereof at high speed. According to one embodiment, the permanent magnets are radially magnetized, two faces parallel to each other of a given permanent magnet having an orthoradial orientation being magnetized so as to be able to generate a magnetic flux in a radial orientation relative to to an axis of the rotating electrical machine. In one embodiment, the inverter is configured to provide a full wave type control having a variable opening angle. This makes it possible to reduce the magnetic field in the direct axis and to reduce the acoustic noise generated by the radial component of the magnetic flux without reducing the torque developed by the machine. In one embodiment, the opening angle is between 70 and 150 degrees.

In one embodiment, said rotating electrical machine is configured to adapt an advance angle to the opening of the full wave control according to a speed of the electric machine. This makes it possible to obtain a negative current in the direct axis adapted as a function of the speed of the machine which reduces the magnetic noise while maintaining an optimal performance that is little or no degradation. In one embodiment, the opening angle of opening is between 60 degrees and 100 degrees.

The advance angle is defined by the electrical angle between the vacuum electromotive force of a phase and the voltage applied across it. According to one embodiment, the stator comprises at least three electrical phases. In a variant, the stator comprises a three-phase double-phase winding, or more generally a polyphase type winding with any number N of phases.

In one embodiment, the three electrical phases are coupled in a triangle. The triangle coupling allows for a smaller wire diameter and a higher number of turns to be easier to adjust at low voltage. In a variant, the coupling may be a star-type coupling.

In one embodiment, the permanent magnets are of the buried type.

According to one embodiment, the rotor comprises a plurality of cavities each housing at least one permanent magnet, two adjacent cavities being separated by an arm belonging to the rotor body, the arm having in particular a thickness greater than or equal to 2 mm. For example, the thickness of an arm is between 2 and 3.6mm.

In one embodiment, a ratio between a thickness of an arm divided by a thickness of a permanent magnet is between 0.5 and 1.2. This makes it possible to obtain a machine whose saliency coefficient is optimized for the present application.

In one embodiment, the rotor is surface magnets, and has interpolar spaces between two adjacent magnets made of magnetic material. According to one embodiment, the machine is configured to rotate at maximum speeds of between 10,000 and 100,000 revolutions per minute.

According to one embodiment, an outer diameter of the rotor is between 20 and 35 mm, and is preferably of the order of 30 mm. The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given for illustrative but not limiting of the invention.

Figure 1 is a sectional view of a turbocharger comprising a rotary electric machine according to the present invention;

Figures 2a and 2b are respectively perspective and cross-sectional views of the rotor of the rotating electrical machine according to the invention;

Figure 3 is a perspective view of the stator of the rotating electrical machine according to the present invention;

FIG. 4 is a schematic representation of the inverter controlling the phases of the rotating electrical machine according to the invention;

Fig. 5 is a diagram of the state of the inverter switching elements as well as phase voltages for full-wave type control as a function of the rotation angle of the rotor;

FIG. 6 is a diagram illustrating in particular the configuration of the currents in the reference frame formed by a direct axis and a quadrature axis;

Figure 7 is a timing diagram illustrating the advance angle between the vacuum electromotive force of a phase and the voltage applied thereto. Identical, similar or similar elements retain the same reference from one figure to another.

FIG. 1 shows an electric compressor 1, comprising a turbine 2 equipped with fins 3 able to suck, via an inlet 4, uncompressed air coming from an air source (not represented) and to repress the compressed air via the outlet 5 after passing through a volute referenced 6. The output 5 may be connected to an inlet distributor (not shown) to optimize the filling of the cylinders of the engine.

In this case, the suction of the air is carried out in an axial direction, that is to say along the axis of the turbine 2, and the discharge is carried out according to a radial direction perpendicular to the axis of the turbine 2. Alternatively, the suction is radial while the discharge is axial. Alternatively, the suction and the discharge are made in the same direction relative to the axis of the turbine (axial or radial). For this purpose, the turbine 2 is driven by an electric machine 7 mounted inside the housing 8. This electric machine 7 comprises a stator 9, which may be polyphase, surrounding a rotor 10 with the presence of an air gap. This stator 9 is mounted in the housing 8 configured to rotate a shaft 1 1 through bearings 14. The shaft 1 1 is connected in rotation with the turbine 2 and with the rotor 10. The stator 9 is preferably mounted in the housing 8 by hooping.

The electric machine 7 has a short response time of less than 300 ms to go from 0 to 70000 revolutions / min. Preferably, the operating voltage is 12 V or 48 V and a steady state current is in the range of 150 A to 260A. Preferably, the electrical machine 7 is able to provide a current peak, that is to say a current delivered over a continuous duration of less than 3 seconds, between 150 A and 800 A, in particular between 180 A and 220 A. .

More precisely, as shown in FIG. 2a, the rotation axis rotor X corresponding to the axis of the machine is permanent magnets. The rotor body 17 is a bundle of sheets formed by an axial stack of sheets on one another. This rotor body 17 is made of ferromagnetic material. The sheets are held by fixing means, for example rivets 18, passing axially right through the rotor body 17. The rotor body 17 can be rotatably connected to the shaft 11 in various ways, for example by force-fitting the splined shaft 1 1 inside the central opening 20 of the rotor body 17 or by means of a key device.

The rotor body 17 has an internal diameter D1 for example of the order of 10 mm, and an outer diameter D 2 of between 20 mm and 35 mm, and preferably of the order of 30 mm. Furthermore, an outer diameter of the stator 9 is between 35mm and 80mm, in particular between 45mm and 55mm, for example between 48mm and 52mm. The "buried magnet" type rotor 10 comprises a plurality of cavities 22 intended to each receive at least one permanent magnet 23. Two adjacent cavities 22 are separated by an arm 26 belonging to the rotor body 10. As shown on FIG. 2b, each arm 26 has a thickness E measured in a direction orthoradial with respect to the X axis greater than or equal to 2mm. For example, the thickness E of an arm 26 is between 2 and 3.6mm.

Preferably, a ratio between a thickness E of an arm 26 divided by a thickness of a magnet 23 is between 0.5 and 1.2. This makes it possible to obtain a machine whose saliency coefficient is optimized for the present application.

In this case, two magnets 23 are stacked axially 23 by cavity 22. The permanent magnets 23 have a rectangular parallelepiped shape whose angles can be beveled. The magnets 23 are radially magnetized, that is to say that the two faces parallel to each other having an orthoradial orientation are magnetized so as to be able to generate a magnetic flux in a radial orientation with respect to the X axis.

As is clearly visible in FIG. 2b, where the letters N and S respectively correspond to the North and South poles, the magnets 23 which will be located in two consecutive cavities 22 are of alternating polarity.

The magnets 23 are preferably made of rare earth to maximize the magnetic power of the machine. Alternatively, they may however be made of ferrite according to the applications and the desired power of the electric machine. A magnet 23 may have a thickness of in particular between 3 and 4 mm. The number of cavities 22 is preferably equal to four. It is however possible to increase the number of cavities 22 and corresponding magnets 23 depending on the application.

The rotor body 17 may also comprise two holding flanges (not shown) plated on either side of the rotor 10 on its axial end faces. These holding flanges provide axial retention of the magnets 23 inside the cavities 22 and also serve to balance the rotor 10. The flanges are made of non-magnetic material, for example aluminum.

Furthermore, as can be seen in FIG. 3, the stator 9 comprises a body 29 and a coil 30. The stator body 29 has an annular cylindrical shape with a Y axis intended to coincide with the X axis when the stator 9 is mounted inside the electrical machine 7. The stator body 29 consists of an axial stack of flat sheets held by means of rivets 33.

More specifically, the body 29 has teeth 35 distributed angularly in a regular manner on an inner circumference of a yoke 36. These teeth 35 delimit notches 37, so that each notch 37 is delimited by two successive teeth 35. The yoke 36 thus corresponds to the solid outer annular portion of the body 29 which extends between the bottom of the notches 37 and the outer periphery of the stator body 29. The notches 37 open axially into the axial end faces of the body 29. The notches 37 are also open radially in the internal cylindrical face of the body 29.

To form the winding 30 of the stator 9, several coils 40 are wound around the teeth 35 of the stator 9, here six in number. The protection between the stator body 29 and the coil wire 40 is provided either by an insulator 41 of the paper type, or by plastic by overmoulding or by means of an insert. Since the winding 30 is of three-phase type, each phase is formed by two coils 40.

As shown in FIG. 4, the phases PH1, PH2, PH3 of the electrical machine 7 are connected in a triangle. The phase outputs u, v, w corresponding to a node between two phases PH1, PH2, PH3 are connected to an inverter 44.

The inverter 44 has arms B1, B2, B3. Each arm B1, B2, B3 comprises a first switching element K1, K2, K3 connecting a phase output u, v, w to the supply voltage B + (element called "high side") when it is passing, and a second switching element Κ1 ', Κ2', K3 'connecting this phase output u, v, w to a mass M (element called "low side") when it is passing. The switching elements K1, K2, K3, Κ1 ', K2', K3 'generally take the form of MOSFET power power transistors.

Figure 5 illustrates a generation of full wave control by the inverter 44 during motor mode operation of the rotating electrical machine. According to this command, the control unit alternately controls the "high side" transistors K1, K2, K3 and "low side" Κ1 ', K2', K3 'of an arm B1, B2, B3 of the inverter 44 for connect a phase output u, v, w either to the supply voltage B +, or to the ground M, when the angular position passes a first switching angular threshold equal to 0 (modulo 360 °), or a second angular threshold of switching is 120 °. In other words, the aperture angle A0 of the transistors K1, K2, K3, Κ1 ', Κ2', K3 'is 120 degrees but may alternatively be different, as explained below. The corresponding phase voltages obtained are referenced UPh1 for the voltage measured between the potentials U and V, UPH2 for the voltage measured between the potentials V and W, and UPh3 for the voltage measured between the potentials W and U.

As illustrated in FIG. 6, the rotating electrical machine 7 has a saliency coefficient equal to an inductance in the quadrature axis Lq divided by an inductance in the direct axis Ld. The electric machine 7 is configured so that the saliency coefficient is greater than 1, 2, especially greater than or equal to 1, 5, for example between 1, 5 and 3.

The inverter 44 is configured to generate a negative current in the direct axis ID in the electrical phases PH1; PH2, PH3 of the stator 9 to decrease the magnetic flux in the direct axis cpD, so as to create a positive reluctant torque. For this purpose, the inverter 44 is configured to perform a control of the full wave type having a variable opening angle AO, between 70 and 150 degrees.

In addition, an angle of advance at the opening AA of the full-wave control is adapted according to the speed of the electric machine. This lead angle AA is defined by the electrical angle between the electromotive force (EMF) at one phase and the voltage applied across its terminals. FIG. 7 shows by way of example the advance angle AA between the force electromotive vacuum generator of phase PH1 referenced FemPHI and voltage UPH1 measured between potentials U and V.

This lead angle AA is between 60 degrees and 100 degrees. Thus, at 10000 rpm, an advance angle AA of the order of 60 ° is sufficient but beyond 40000rpm, the lead angle AA increases to 80 degrees and to 100.degree. 70000rpm. Beyond an angle of advance AA of 100 °, the yield is strongly degraded. This makes it possible to obtain a negative current in the D axis that is adapted as a function of the speed of the machine, which reduces the magnetic noise while maintaining optimum performance that is little or no degradation. Alternatively, the rotor 10 is surface magnets 23, and has interpolar spaces between two adjacent magnets 23 made of magnetic material.

As a variant, the phases PH1, PH2, PH3 may be connected in a star.

In a variant, the stator 9 comprises a winding 30 of the double three-phase type. Alternatively, the winding 30 may be of distributed wavy type, the windings being obtained for example from a continuous wire covered with enamel or from conductive elements in the form of U-shaped pins whose free ends are connected together by welding.

Of course, the foregoing description has been given by way of example only and does not limit the scope of the invention which would not be overcome by replacing the different elements by any other equivalent.

In addition, the various features, variations, and / or embodiments of the present invention may be associated with each other in various combinations, to the extent that they are not incompatible or exclusive of each other.

Claims

1. Rotating electric machine (7) arranged to operate at least in engine mode, in particular for an electric turbo-compressor (1) of a motor vehicle, comprising:

a stator (9) comprising a winding (30) provided with a plurality of electrical phases (PH1, PH2, PH3),

a rotor (10) with permanent magnets (23),

said rotating electrical machine (7) having a saliency coefficient equal to an inductance in a quadrature axis (Lq) divided by an inductance in a direct axis (Ld),

an inverter (44) for electrically controlling said rotary electric machine (7),

characterized in that

said rotating electrical machine (7) is configured so that the saliency coefficient is greater than 1, 2, in particular greater than or equal to

1, 5, for example between 1, 5 and 3,

the inverter (44) being configured to generate a negative current in the direct axis (ID) in the electrical phases (PH1, PH2, PH3) of the stator (9) to reduce the magnetic flux in the direct axis (cpD ), so as to create a positive reluctant torque.

2. A rotary electric machine according to claim 1, characterized in that the permanent magnets (23) are radially magnetized, two faces parallel to each other of a given permanent magnet (23) having an orthoradial orientation being magnetized so as to be able to generate a magnetic flux in a radial orientation with respect to an axis (X) of the rotating electrical machine (7).

3. A rotary electric machine according to claim 1 or 2, characterized in that the inverter (44) is configured to provide a full wave type control having a variable opening angle (AO).

4. Rotating electric machine according to claim 3, characterized in that the opening angle (AO) is between 70 and 150 degrees.

5. Rotating electric machine according to any one of the preceding claims, characterized in that it is configured to adapt an angle of advance to the opening (AA) of the full wave control according to a speed of the machine electric.

6. Rotating electric machine according to claim 5, characterized in that the opening angle of opening (AA) is between 60 degrees and 100 degrees.

7. Rotating electrical machine according to any one of the preceding claims, characterized in that the stator (9) comprises at least three electrical phases (PH1, PH2, PH3).

8. rotary electric machine according to claim 7, characterized in that the three electrical phases (PH1, PH2, PH3) are coupled in a triangle.

9. rotating electrical machine according to any one of the preceding claims, characterized in that the permanent magnets (23) are of the buried type.

10. Rotating electric machine according to claim 9, characterized in that the rotor (10) comprises a plurality of cavities (22) each housing at least one permanent magnet (23), two adjacent cavities (22) being separated by an arm ( 26) belonging to the rotor body (17), the arm (26) having in particular a thickness (E) greater than or equal to 2 mm.

1 1. Rotary electric machine according to claim 10, characterized in that a ratio between a thickness (E) of an arm (26) divided by a thickness of a permanent magnet (23) is between 0.5 and 1 .2.

12. A rotary electric machine according to any one of the preceding claims, characterized in that the rotor (10) is surface magnets (23) and has interpolar spaces between two magnets (23) adjacent made of magnetic material.

13. A rotary electric machine according to any one of the preceding claims, characterized in that an outer diameter (D2) of the rotor (10) is between 20 and 35 mm, and is preferably of the order of 30mm.