Wound rotor with reconfigurable magnetic poles and associated excitation system

Abstract

Wound rotor with reconfigurable magnetic poles and associated excitation system The invention relates to a wound rotor (1) and an associated excitation system, the wound rotor (1) comprising angularly distributed coils powered by the excitation system to form magnetic poles (p1, ... p8), and three conductors (A, B, C) connecting the excitation system (2) at least to a first coil connected by one of its ends to a first of the conductors (A) and by the other of its ends to a second of the conductors (B), and to a second coil connected by one of its ends to the second conductor (B) and by the other of its ends to a third of the conductors (C), a first voltage between the first conductor (A) and the second conductor (B) and a second voltage between the second conductor (B) and the third conductor (C) being of the same sign or of opposite sign depending on the magnetic configuration chosen for the wound rotor (1).(Figure 2).

Description

Title of the invention: Wound rotor with reconfigurable magnetic poles and associated excitation system

[0001] The present invention relates to the field of electrical engineering, and more specifically concerns an electrical machine finding a particularly advantageous application in the automotive field. The invention applies in particular to the powertrains of electric or hybrid vehicles.

[0002] The sizing of an electric traction or propulsion machine for an electric or hybrid vehicle is always the result of a compromise to be found between several performance axes: - the machine must be able to deliver a maximum torque sufficiently high to accelerate and brake the vehicle over a relatively short period of time, - the machine must be able to deliver a sufficiently high maximum continuous power over a long period of time, to ensure good robustness in recovery, adapted to a dynamic driving profile, - the machine must be of reduced size, mass and cost, and finally - the energy efficiency of the machine must be as good as possible, for the benefit of good vehicle autonomy or a reduced size of a high-voltage vehicle battery.

[0003] One way to meet these expectations could be, in an electric vehicle, the use of mechanical transmissions with two or more reduction ratios, instead of a single-ratio reducer. Indeed, this could lead to sizing a smaller machine than the traction machines usually used in electric vehicles. This small machine would have a more restricted maximum torque, but better continuous performance and better efficiency by reducing its rotational speed.

[0004] However, this route is not used due to its higher cost and especially because of its impact on the driving pleasure, one of the strengths of electric vehicles being the absence of changing transmission ratio, which offers driving without any interruption of accelerations or decelerations.

[0005] Another optimization route may consist of a change in the configuration of the winding of the electric machine, making it possible to switch, depending on the operating point of the vehicle, from a “low speed” configuration, provided with an optimal torque density, to a “high speed” configuration, with a better power density and reduced energy losses. The torque density here corresponds to the ratio between the torque capacity of the machine and its volume, and the power density corresponds to the ratio between the power capacity of the machine and its volume.

[0006] This type of dual configuration electrical machine exists, several devices having been used in industry. In particular, the coupling of the stator windings of certain electrical machines can be modified, by switching from a star connection with neutral, to a delta connection.

[0007] Other devices, such as induction machines (or asynchronous machines), allow their number of stator pole pairs to be changed. Such an electrical machine therefore has several configurations in which the number of stator poles is different. This is the case of so-called double-speed Dahlander machines. Such a device is possible with an induction machine without changing the configuration of its rotor because the polarity of the rotor results from the currents induced in its rotor circuit, themselves resulting from the magnetic flux generated by the stator of the machine. The polarity of the rotor is therefore necessarily adapted to that of the stator.

[0008] Adapting such a configuration change to a synchronous machine requires adapting the number of rotor poles to the number of stator poles during the configuration change, in order to maintain a magnetic coupling allowing the generation of mechanical torque and the transformation of power. This is not achievable with a permanent magnet rotor, since the polarity of such a rotor is linked to its geometry.

[0009] With a wound rotor, this requires a change in the power supply to the rotor windings. When the wound rotor is in operation, therefore rotating, such a change in power supply is a priori unfeasible without oversizing the excitation system of the wound rotor as well as the rotor itself, and without complicating the connections of the rotor windings to the excitation system. In particular, the end of the rotor shaft would have to have many more than two power supply rings, which would lengthen the size of the rotor.

[0010] It is possible to envisage a hybrid wound rotor, i.e. one comprising both permanent magnets and rotor windings, but such a wound rotor, simpler to power, would lead to strong asymmetries in the magnetic circuit. The efficiency and vibration behavior of the machine would be impacted, as well as the control of the machine, which would therefore be more complex. In addition, the winding would be more constrained in terms of size. All of this is detrimental to an industrial application of such a reconfigurable rotor.

[0011] The present invention aims to remedy at least in part the aforementioned drawbacks by providing a wound rotor and excitation system assembly, and an electrical machine comprising such an assembly, which make it possible to reconfigure the polarity of the rotor winding without significant additional cost or oversizing, and thus to obtain, by symmetrically polarizing the stator winding, an electric machine with two configurations, one having a high torque density at low speed and the other having a high power density at high speed.

[0012] To this end, the invention proposes a wound rotor assembly and electrical excitation system for the wound rotor, the wound rotor comprising a plurality of coils distributed angularly around the wound rotor and capable of being powered by the excitation system to form magnetic poles, said assembly being characterized in that the wound rotor comprises at least three conductors electrically connecting the excitation system to at least two angularly adjacent coils of the plurality of coils, a first of the coils being connected by one of its ends to a first of the conductors and by the other of its ends to a second of the conductors, a second of the coils being connected by one of its ends to the second conductor and by the other of its ends to a third of the conductors, and in that the excitation system is capable of applying a first voltage between the first conductor and the second conductor and a second voltage between the second conductor and the third conductor, the first and second voltages being of the same sign or of opposite sign depending on a choice between a first magnetic configuration of the wound rotor and a second magnetic configuration of the wound rotor.

[0013] Thanks to the invention, only three conductors connect the excitation system to the coils of the wound rotor, which makes it possible not to lengthen the shaft of the wound rotor or to lengthen it very little in order to put there, for example, three conductive rings each corresponding to one of the three conductors and traversed by three brushes of the excitation system. The coils form, on a body of the wound rotor, magnetic poles which can be salient or smooth. When the poles are salient, each coil surrounds a tooth of the rotor body extending over the axial length of the rotor body by projecting from it. The angularly adjacent coils therefore each surround two adjacent teeth on the periphery of the rotor body. When the poles are smooth, each coil axially surrounds the rotor body over an angular portion thereof, and the angularly adjacent coils therefore cross on the axial ends of the rotor body.

[0014] It should be noted that in this patent application, the terms "axial" (or "axial") refer, unless otherwise stated, to a direction parallel to an axis of rotation of the wound rotor in the electrical machine that incorporates it. Similarly, the terms "radial" refer, unless otherwise stated, to a direction orthogonal to the axis of rotation of the rotor of the electrical machine, and secant to this axis of rotation, whereas the terms "angular" or "ortho-radial" refer, unless otherwise stated, to a direction orthogonal to the axial direction and to a radial direction, this orthogonal direction being in fact rotating around the axis of rotation of the rotor.

[0015] In one embodiment of the invention, the plurality of coils of the wound rotor comprises at least one other pair of coils adjacent to the two adjacent coils, this other pair of adjacent coils comprising a third coil and a fourth coil, the first, second, third and fourth coils following each other angularly and having the same winding direction from a first end of the coil to a second end of the coil relative to a radial direction, - the second end of the first coil and the first end of the second coil being connected to the second conductor, - the second end of the second coil and the first end of the third coil being connected to the third conductor, - the second end of the third coil and the first end of the fourth coil being connected to the second conductor, and - the second end of the fourth coil and the first end of the first coil being connected to the first conductor.

[0016] It is understood that in this embodiment of the invention, said one of the ends of the first coil and said one of the ends of the second coil are first ends respectively of the first coil and of the second coil, and said other of the ends of the first coil and said other of the ends of the second coil are second ends of the first coil and respectively of the second coil.

[0017] This embodiment facilitates the assembly and connection of the coils on the wound rotor. Of course, many other alternative embodiments are conceivable, in which the coils are not all wound in the same direction from their first ends to their second ends relative to the radial direction. For example, as a variant, the third and fourth coils have first and second ends connected like those respectively of the first and second coils to the three conductors, but the second and third coils have, from their first ends to their second ends, winding directions opposite those of the first and fourth coils.

[0018] It should be noted that the direction of winding of a coil is defined by its winding around the radial direction, oriented for example towards the outside of the wound rotor, this orientation being fixed for all the coils whose winding direction is considered. Thus the winding direction corresponds to a clockwise or anticlockwise direction. clockwise around this oriented radial direction. The winding direction determines the direction of the magnetic field when current flows from the first end of a coil to the second end of the coil. It may be different from a winding direction which is related to the assembly process.

[0019] In this embodiment of the invention, when the wound rotor comprises an even number of coils connected to the three conductors, greater than 4, it reproduces, following the fourth coil, the connections of the first and second coils, then depending on the number of coils of the wound rotor, the third and fourth coils, and so on until reaching the first coil. The same applies in the previously mentioned variant, in which the third and fourth coils are connected like the first and second coils to the three conductors.

[0020] According to an optional but advantageous characteristic of the invention, the wound rotor further comprises a coil head guide pressed against an axial end of a cylindrical body of the wound rotor on which the coils are mounted, the coil head guide comprising winding pads for each first end of one of the coils and for each second end of a coil adjacent to said coil, the pads being capable of guiding the first and second ends towards a space angularly between the two coils for the connection of the first end to the second end.

[0021] This feature then simplifies the electrical connection of the ends of the rotor coils to the three conductors, one connection per coil being sufficient to make this electrical connection, the connection per coil being a common connection between two adjacent coils. This connection is made for example by welding and / or crimping in an electrical terminal of one of the conductors.

[0022] The three conductors each comprise, for example, a conductive ring arranged on one end of a rotating shaft of the wound rotor, the excitation system comprising at least one conductive brush per ring, capable of supplying the ring with current during a rotation of the wound rotor. Each conductor therefore comprises a ring, connected to the ends of the rotor coils, for example, by means of electrical wires and electrical terminals. Each electrical wire is, for example, arranged in an axial groove of the rotor shaft up to the proximity of the coil head guide, where the electrical wire extends radially to an electrical terminal in which a first end and a second end of two adjacent coils are welded and / or crimped together, this electrical terminal being located in the space between the two adjacent coils.

[0023] In one embodiment of the invention, the excitation system comprises a voltage converter stage comprising: - a positive input terminal and a negative input terminal capable of being connected to a direct voltage source, - a first, a second and a third switching arm connected to the input terminals and each comprising a midpoint connected respectively to the first conductor, to the second conductor and to the third conductor.

[0024] This embodiment of the invention, with a three-arm converter, greatly simplifies the excitation system by not requiring two voltage sources or two voltage converters whose connections to the second conductor of the wound rotor would be reconfigurable by switches.

[0025] In this embodiment of the invention: - the first switching arm comprises a switch connected between the positive input terminal and its midpoint, and a diode connected between its midpoint and the negative input terminal, - the second switching arm comprises a switch connected between the negative input terminal and its midpoint, and a diode connected between its midpoint and the positive input terminal, and - the third switching arm comprises a first switch connected between the positive input terminal and its midpoint, and a second switch connected between the negative input terminal and its midpoint.

[0026] This configuration of the three-arm converter has the advantage of being inexpensive compared to other configurations in which the converter comprises, for example, six transistors.

[0027] The assembly according to the invention comprises, in this embodiment of the invention, a control circuit capable of applying: - in the first magnetic configuration of the wound rotor, a first non-zero duty cycle aH at the switch of the first arm, a second duty cycle [3L equal to one at the switch of the second arm, a third non-zero duty cycle yH at the first switch of the third arm, and a fourth duty cycle yL less than (1- yH) at the second switch of the third arm, and - in the second magnetic configuration of the wound rotor, a first non-zero duty cycle aH at the switch of the first arm, a second zero duty cycle [3L at the switch of the second arm, a third zero duty cycle yH at the first switch of the third arm, and a fourth duty cycle yL equal to one at the second switch of the third arm.

[0028] Preferably, the first duty cycle aH is chosen to be equal to the third duty cycle yH in the first configuration of the wound rotor, to balance the currents in the coils of the wound rotor.

[0029] The invention also relates to an electrical machine comprising an assembly according to the invention, a stator with reconfigurable magnetic poles and means of changing the configuration of the stator between, on the one hand, a third magnetic configuration in which the number of magnetic poles of the stator is identical to the number of magnetic poles of the wound rotor in the first magnetic configuration, and on the other hand, a fourth magnetic configuration in which the number of magnetic poles of the stator is identical to the number of magnetic poles of the wound rotor in the second magnetic configuration, the means for changing the configuration of the stator comprising means for selecting the third or fourth magnetic configuration as a function of the first or second magnetic configuration chosen for the wound rotor.

[0030] The selection means are configured to choose the third configuration when the rotor is in the first configuration, and to choose the fourth configuration when the rotor is in the second configuration. They are for example coupled to the control circuit.

[0031] The invention also relates to an electric or hybrid vehicle comprising an electric machine according to the invention.

[0032] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several exemplary embodiments given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0033] [Fig-1] is a front view of a wound rotor of an assembly according to the invention, mounted in an electrical machine according to the invention, in one embodiment of the invention,

[0034] [Fig.2] is a schematic representation of the wound rotor of [Fig.l], in a first configuration of its magnetic poles,

[0035] [Fig.3] is a schematic representation of the wound rotor of [Fig.l], in a second configuration of its magnetic poles,

[0036] [Fig.4] is a schematic representation of a voltage converter of an excitation system of the entire embodiment of [Fig.l], in the first configuration of the magnetic poles of the wound rotor,

[0037] [Fig.5] is a schematic representation of the voltage converter of [Fig.4], in the second configuration of the magnetic poles of the wound rotor,

[0038] [Fig.6] is a schematic representation of a reconfigurable stator of the electrical machine comprising the wound rotor of [Fig.l], in a third configuration of magnetic poles specific to the stator,

[0039] [Fig.7] is a schematic representation of the reconfigurable stator of [Fig.6], in a fourth magnetic pole configuration specific to the stator, and

[0040] [Fig.8] reproduces a first curve of torques delivered by the electric machine in the configuration of [Fig.6] and a second curve of torques delivered by the electric machine in the configuration of [Fig.7], depending on the rotation speed of the electric machine.

[0041] According to an embodiment of the invention shown in [Fig.l], an electrical machine according to the invention comprises a wound rotor 1 with eight magnetic poles p1 to p8, projecting radially from a body of the wound rotor 1, of overall cylindrical shape. The eight magnetic poles p1 to p8 follow each other angularly in this order around the rotor body. The body of the rotor is integral at its center with a rotating shaft, mounted to rotate in the electrical machine, around an axis of rotation X.

[0042] The body of the wound rotor 1 comprises eight magnetic steel teeth, angularly distributed around the wound rotor 1 and extending axially on the cylindrical part of the rotor body, from one axial end thereof to the other. Each of the teeth is wound by a conductive wire for example made of copper, the coil bl, ..., b8 thus formed having the same winding direction from a first of its ends respectively 11, ..., 81 to a second of its ends respectively 12, ..., 82, for example in the counterclockwise direction around a radial direction oriented towards the outside of the wound rotor 1. In [Fig.l], the coil bl is thus wound in the counterclockwise direction around the radial direction R oriented towards the outside of the wound rotor 1 from its first end 11 to its second end 12.The coils bl to b8 thus assembled on the wound rotor 1 form, when they are traversed by an electric current, the respective magnetic poles pl to p8. By abuse of language, in this embodiment of the invention, each salient pole of the wound rotor 1 is assimilated to its magnetic pole facing the air gap of the electric machine.

[0043] The coils b1 to b8 are electrically insulated from the rotor body in particular by a coil head guide 9 arranged at each axial end of the rotor body. Each coil head guide 9, for example made of polymer material, comprises a central body with a hole in its center to allow the rotating shaft to pass through. From this central body extend eight branches, each pressed against an axial end of a tooth. On this axial end, the branch is therefore located between the tooth and the coil surrounding the tooth.

[0044] Between each of the branches, the central body of the coil head guide 9 comprises a space 90 in which each first end 11, ..., 81, of one of the respective coils bl, ..., b8 is brought to facilitate its insertion then its crimping and / or welding in an electrical terminal (not shown) connected by a conductive bar to a ring of an electrical conductor A, B or C. There are therefore eight electrical terminals distributed around the rotating shaft of the wound rotor 1. Each electrical terminal receives a first end 11, ..., 81 of a respective coil bl, ... b8 and a respective second end 82, ..., 12 of an adjacent coil respectively b8, .. .bl to this respective coil bl, ..., b8. The second end 82, ..., 12 is also brought into one of the spaces 90 to facilitate its insertion then its crimping and / or welding in the electrical terminal. In [Fig.l], welding points s (as referenced for example between coils b3 and b4) represent the connections of the coil ends to the conductive bars.

[0045] On either side of a plane of axial symmetry of each tooth, parallel to a radial direction, the coil head guide 9 comprises on its central body, two winding pads 92 almost touching the coil surrounding this tooth, and close to each other. The first end of the coil is wound around one of the two winding pads 92, proximal to this first end and to a space 90, to open into this space 90, and the second end of the coil is wound around the other of the two winding pads 92, proximal to this second end and to another space 90, to open into this other space 90. These winding pads 92 facilitate the correct positioning of the ends of the coils in a space 90 to then crimp and / or solder them in an electrical terminal.

[0046] The three conductors A, B, C each comprise a conductive ring, and conductive bars each connected to the ring of the corresponding conductor and to the electrical terminals of the corresponding conductor, in which coil ends are welded and / or crimped as described above. These rings are shown concentric in [Fig.l], to better visualize them, whereas these rings are in reality of the same diameter and axially offset from each other so as to each be traversed by a conductive brush of an excitation system 2 (referenced [Fig.4] in particular) when the wound rotor 1 is rotating.

[0047] More precisely, in this embodiment where the coils b1 to b8 follow each other angularly in this order:

[0048] - the first ends 11 and 51 of the coils bl and b5, as well as the second ex ends 82 and 42 of coils b8 and b4, are electrically connected to the first conductor A,

[0049] - the first ends 21, 41, 61 and 81 of the coils b2, b4, b6 and b8, as well as the second ends 12, 32, 52 and 72 of the coils bl, b3, b5 and b7, are electrically connected to the second conductor B, and

[0050] - the first ends 31 and 71 of the coils b3 and b7, as well as the second ex ends 22 and 62 of coils b2 and b6, are electrically connected to the third conductor C.

[0051] Thanks to these electrical connections, schematically reproduced in [Fig.2], when a first positive voltage Vfl is applied between conductor A, of higher electrical potential, and conductor B of lower electrical potential, and when a second positive voltage Vf2 is applied between conductor C, of ​​the same electrical potential as conductor A, and conductor B, the poles pl, p3, p5 and p7 form magnetic north poles (referenced N) while the poles p2, p4, p6 and p8 form magnetic south poles (referenced S).

[0052] The wound rotor 1 is then in a first magnetic configuration in which each coil bl, ... b8 having a magnetic north pole in the air gap of the electric machine, is immediately followed and preceded angularly by a coil of the wound rotor 1 having a magnetic south pole in the air gap of the electric machine. Similarly in this first configuration, each coil bl, ... b8 having a magnetic south pole in the air gap of the electric machine, is immediately followed and preceded angularly by a coil of the wound rotor 1 having a magnetic north pole in the air gap of the electric machine. In other words, each salient pole of the wound rotor 1 is magnetized differently from its nearest neighboring salient poles, which means that the wound rotor 1 has eight magnetic poles seen from a stator 3 (referenced figures 6 and 7) of the electric machine.

[0053] As visible in [Fig.3], when a first positive voltage Vfl is applied between conductor A, of higher electrical potential, and conductor B of lower electrical potential, and when a second negative voltage Vf2 is applied between conductor B and conductor C of lower electrical potential than conductor B, poles pl, p2, p5 and p6 form magnetic north poles (referenced N) while poles p3, p4, p7 and p8 form magnetic south poles (referenced S).

[0054] The wound rotor 1 is then in a second magnetic configuration in which the wound rotor 1 has only four magnetic poles seen from the stator 3 of the electrical machine. Indeed, the coils bl, ... b8 of the wound rotor 1 have two by two, that is to say in pairs of angularly adjacent coils, the same north or south magnetization.

[0055] A voltage converter stage of the excitation system 2 of the electrical machine will now be described in relation to [Fig. 4]. The excitation system 2 comprises a voltage source, delivering a direct voltage UDC between a positive terminal H and a negative terminal L of the excitation system 2. A capacitor is connected in parallel to the direct voltage source. Three switching arms a1, a2, a3 of the voltage converter stage are also each connected in parallel to the direct voltage source, a first end of each of the arms a1, a2, a3 being connected to the positive terminal H, and a second end of each of the arms a1, a2, a3 being connected to the negative terminal L.

[0056] The first switching arm al comprises a controlled switch connected between the first end of the first arm al and a midpoint of the first arm al, and a diode connected between the midpoint of the first arm al and the second end of the first arm al. The anode of the diode is therefore connected to the negative terminal L while the cathode of the diode is connected to the midpoint of the first arm al. The controlled switch is here a bipolar transistor whose emitter is connected to the midpoint of the first arm al and the collector to the positive terminal H. A diode is connected in antiparallel to the transistor. The transistor of the first arm al is controlled with a duty cycle aH, by a control circuit (not shown) of the excitation system 2.

[0057] Finally, the midpoint of the first arm al is connected to the first conductor A, so that a current arriving in the transistor of the first arm al flows in the first conductor A via a conductive brush of the excitation system 2, for example a carbon brush.

[0058] The second switching arm a2 comprises a controlled switch connected between the second end of the second arm a2 and a midpoint of the second arm a2, and a diode connected between this midpoint and the first end of the second arm a2. The cathode of this diode is therefore connected to the positive terminal H while the anode of the diode is connected to the midpoint of the second arm a2.

[0059] The controlled switch of the second arm a2 is also a bipolar transistor whose emitter is connected to the negative terminal L and the collector to the midpoint of the second arm a2. A diode is connected in antiparallel to this transistor, controlled with a duty cycle [3L, by the control circuit.

[0060] Finally, the midpoint of the second arm a2 is connected to the second conductor B, so that a current arriving from the second conductor B flows in the transistor of the second arm a2 via a conductive brush of the excitation system 2.

[0061] The third switching arm a3 comprises a first controlled switch connected between the first end of the third arm a3 and a midpoint of the third arm a3, and a second controlled switch connected between the second end of the third arm a3 and the midpoint of the third arm a3. The first and second controlled switches are also bipolar transistors. The collector of the first transistor is therefore connected to the positive terminal H and the emitter of the first transistor is connected to the midpoint of the third arm a3 and to the collector of the second transistor, the emitter of which is connected to the negative terminal L. A diode is connected in antiparallel across the terminals of each of the first and second transistors. The first transistor is controlled with a duty cycle yH and the second transistor with a duty cycle yL. These controls are carried out by the control circuit of the excitation system 2.

[0062] Finally, the midpoint of the third arm a3 is connected to the third conductor C, so that a current arriving in the first transistor of the third arm flows in the third conductor C via a conductive brush of the excitation system 2. Similarly, a current arriving from the third conductor C flows in the second transistor of the third arm a3 thanks to this conductive brush.

[0063] In the first magnetic configuration, so that the wound rotor 1 has eight magnetic poles seen from the stator 3, the first positive voltage Vfl equal to the voltage UAB between the conductor A and the conductor B, and the second positive voltage Vf2 equal to the voltage UCB between the conductor C and the conductor B, are regulated respectively by means of the respective duty cycles aH and yH:

[0064] Vfl=aH*UDCet

[0065] Vf2=yH*UDC

[0066] For a current ifl flowing between ring A and ring B to reach a current setpoint ifl*, and for a current if2 flowing between ring C and ring B to reach a current setpoint if2* identical to the current setpoint ifl*, we choose Vfl = Vf2 therefore aH=yH. This condition is however not necessary, the regulators of the currents ifl and if2 naturally adjust the control voltages which depend on the resistances of the windings. Alternatively, the same regulator imposes aH=yH and therefore the equality of the voltages Vfl and Vf2.

[0067] Furthermore, in this first configuration, we have [3L = 1 and yL = 1 - yH, respecting a dead time between the opening of the first transistor and the closing of the second transistor of the third arm a3 (so in fact yL < 1 - Yh)• More precisely: yL = min(0.1-yH-TM) with TM the duration of the dead time

[0068] In this first configuration, the current flows as shown [Fig.4] with the arrows:

[0069] - the current ifl flows from the positive terminal H into the transistor of the first arm al, then into conductor A, then into conductor B, and finally into the transistor of the second arm a2 before reaching the negative terminal L.

[0070] - the current if2 flows from the positive terminal H into the first transistor of the third arm a3, then into conductor C, then into conductor B, and finally into the transistor of the second arm a2 before reaching the negative terminal L.

[0071] We therefore have a current flowing in conductor B equal to -ifl-if2, i.e. double the current flowing in each of the rotor coils, taking ifl = if2.

[0072] Therefore, by way of example, for an electrical machine according to the invention with an electrical power of 100kW to 200kW (kiloWatt), the transistors of the first and third arms a1 and a3 are sized so that they each support 20A, and the transistor of the second arm a2 so that it supports a current of 40A when it is not used to cut current (therefore it can be sized to support a little less than 40A in a cutting situation).

[0073] In the second magnetic configuration, so that the wound rotor 1 has four magnetic poles seen from the stator 3, the positive voltage Vf equal to the voltage UAC between the conductor A and the conductor C is regulated thanks to the duty cycle aH of the first arm al:

[0074] Vf = aH * UDC

[0075] Furthermore, in this second configuration, we have:

[0076] yH = 0

[0077] YL= 1

[0078] |3l= 0

[0079] In this second configuration, no dead time is necessary, and no current flows in conductor B. We therefore have:

[0080] UAB = UBC = Vf / 2 = Vfl = -Vf2

[0081] In this second configuration, a current if flows as shown [Fig.5] with the arrows: the current if flows from the positive terminal H into the transistor of the first arm a1, then into the conductor A, then into the conductor C, and finally into the second transistor of the third arm a3 before reaching the negative terminal L.

[0082] Finally, in the first and second configurations, the demagnetization of the wound rotor 1 is carried out by opening all the switches of the voltage converter stage:

[0083] aH = 0; Yh = 0; Yl= 0; [3L= 0

[0084] A stator 3 with reconfigurable magnetic poles, usable in the electrical machine according to the invention, will now be described in relation to Figures 6 and 7. Many other types of stator with reconfigurable magnetic poles can of course be used, in which the coils are for example connected in a delta or star configuration, or in which the power supply or the winding of the magnetic poles uses configurations other than those of Figures 6 and 7.

[0085] The stator 3 is three-phase and comprises, per phase, eight stator windings capable of forming, when they are supplied together, eight magnetic poles PI to P8, presenting a north or south pole to the wound rotor 1 depending on the currents flowing through them, these currents varying over time.

[0086] Figures 6 and 7 are schematic representations of stator windings in the slots of the stator 3, these being shown one after the other as if the interior of the stator 3 were unrolled flat in these figures.

[0087] To simplify, Figures 6 and 7 only show the stator windings corresponding to a first supply phase of the stator 3, the stator windings of two other supply phases being present in notches of the stator 3 located angularly between the notches of the stator 3 filled by the stator windings of the first supply phase. The configurations of the stator windings of the second and third supply phases are obtained by translating the configuration of the stator windings of the first supply phase by two notches and four notches respectively to the right. (in the PI to P8 direction) in each of figures 6 and 7.

[0088] Each magnetic pole P1 to P8 extends over six consecutive notches out of the forty-eight notches shown. The magnetic poles P1 to P8 follow each other angularly in this order on the circumference of the stator 3. Every other magnetic pole is not reconfigurable, that is to say its electrical supply diagram is not modified. As a result, the stator windings of these poles P2, P4, P6 and P8 are not shown at all in Figures 6 and 7.

[0089] Furthermore, to simplify the explanation of Figures 6 and 7, these Figures 6 and 7 are placed at a time when the supply currents of the phases of the stator 3 in [Fig.6] are identical to those of [Fig.7]. At this time, the non-reconfigurable poles P2, P4, P6 and P8 each have a south pole (referenced S) to the wound rotor 1.

[0090] The reconfigurable magnetic poles of the stator 3 comprise:

[0091] - the first magnetic pole PI, formed (in part since there are three phases, this precision not being mentioned thereafter) of a first winding of the first supply phase, this first winding having a first end Al at a first notch located between the first magnetic pole PI and the eighth magnetic pole P8, and a second end connected to a first end of a fifth winding of the first supply phase forming the fifth magnetic pole P5;

[0092] - the fifth magnetic pole P5, formed by the fifth winding of the first supply phase, the first end of this fifth winding being at a notch located between the fourth magnetic pole P4 and the fifth magnetic pole P5, and a second end A2 of this fifth winding being connected to a first end A3 of a third winding of the first supply phase forming the third magnetic pole P3;

[0093] - the third magnetic pole P3, formed by the third winding of the first power supply phase, the first end A3 of which is at a notch located between the second magnetic pole P2 and the third magnetic pole P3 and a second end of which is connected to a first end of a seventh winding of the first power supply phase forming the seventh magnetic pole P7;

[0094] - and the seventh magnetic pole P7, formed by the seventh winding of the first power supply phase, the first end of which is at a notch located between the sixth magnetic pole P6 and the seventh magnetic pole P7, and the second end A4 of which is at a notch located between the seventh magnetic pole P7 and the eighth magnetic pole P8.

[0095] Each winding of the first power supply phase has the same winding direction from its first end to its second end, here a direction clockwise relative to a radial direction directed towards the wound rotor 1.

[0096] In a third magnetic configuration illustrated [Fig.6], specific to the stator 3, the first end A1 of the first winding forming the first magnetic pole P1 is connected to a first output of a power inverter of the electrical machine according to the invention, this first output delivering the power supply current of the first phase of the stator 3. The second end A4 of the seventh winding forming the seventh magnetic pole P7 is connected to a neutral point of the electrical machine (it is assumed here that the stator windings are connected in star).

[0097] In this third magnetic configuration, as represented by the solid white arrows in [Fig.6], the supply current of the first phase of the stator 3 flows in the windings from the magnetic pole PI to the magnetic pole P5, then to the magnetic pole P3, then to the magnetic pole P7, these four magnetic poles PI, P3, P5, P7 then forming north poles seen from the wound rotor 1.

[0098] In the third magnetic configuration, the stator 3 therefore has, seen from the wound rotor 1, eight magnetic poles alternating between a north pole and a south pole.

[0099] In a fourth magnetic configuration illustrated [Fig.7], specific to the stator 3, the first end A1 of the first winding forming the first magnetic pole PI is connected to the second end A4 of the seventh winding forming the seventh magnetic pole P7, these two ends themselves being connected to the first output of the power inverter of the electric machine. In addition, the first end A3 of the third winding forming the third magnetic pole P3 is connected to the second end A2 of the fifth winding forming the fifth magnetic pole P5, these two ends themselves being connected to the neutral point of the electric machine.

[0100] In this fourth magnetic configuration, as represented by the solid white arrows in [Fig.7], a first part of the supply current of the first phase of the stator 3 flows in the winding of the first magnetic pole PI then in the second magnetic pole P5 before reaching the neutral point, and a second part of the supply current of the first phase of the stator 3 flows in the winding of the seventh magnetic pole P7 then in the third magnetic pole P3 before reaching the neutral point. The magnetic poles PI and P5 then form north poles seen from the wound rotor 1, while the magnetic poles P3 and P7 form south poles seen from the wound rotor 1.

[0101] In the fourth magnetic configuration, the stator 3 therefore has four magnetic poles on the wound rotor 1, each of these magnetic poles being formed from two adjacent stator windings, i.e. on twelve consecutive notches.

[0102] The electrical machine according to the invention comprises means making it possible to pass from the third configuration to the fourth configuration and vice versa, these means comprising controlled switches. These controlled switches are for example controlled by a computer of a vehicle integrating the electric machine according to the invention, the computer selecting the third configuration for the stator 3 when the wound rotor 1 is in its first configuration, and selecting the fourth configuration for the stator 3 when the wound rotor 1 is in its second configuration.

[0103] In [Fig.8] are represented:

[0104] - a curve Cl of a torque T provided by the machine according to the invention, as a function the rotational speed of wound rotor 1 in revolutions per minute (RPM) when wound rotor 1 is in its first magnetic configuration and stator 3 is in the third magnetic configuration, and

[0105] - a curve C2 of the torque T supplied by the machine according to the invention, as a function of the rotational speed of wound rotor 1 in revolutions per minute when wound rotor 1 is in its second magnetic configuration and stator 3 is in the fourth magnetic configuration.

[0106] It can be seen that at low speed, the first configuration of the wound rotor 1 associated with the third configuration of the stator 3 makes it possible to deliver a greater torque than the second configuration of the wound rotor 1 associated with the fourth configuration of the stator 3, which is useful for starting the vehicle.

[0107] At high speed, the second configuration of the wound rotor 1 associated with the fourth configuration of the stator 3 provides more power than the first configuration of the wound rotor 1 associated with the third configuration of the stator 3, which allows good pick-up for a driver with a dynamic driving profile.

[0108] This high starting torque and this high power at high speed are obtained with an electric machine having smaller components than those of an electric machine which would have a single torque curve as a function of the rotational speed of its rotor, this single curve enveloping both curve C1 and curve C2.

[0109] The electric machine according to the invention therefore provides additional degrees of freedom compared to the existing system to improve the torque density of an electric machine, its power density, the sizing of its inverter, the extent of its operating zone with good efficiency, its thermal behavior and its cost. This is due in particular to the fact that the electric machine according to the invention makes it possible to control the amplitude of the magnetic excitation of the electric machine compared to reconfigurable asynchronous machines, which makes it possible to optimize this magnetic excitation to maximize the efficiency of the machine at all its operating points.

[0110] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. For example, the stator of the electrical machine according to the invention may comprise more than three phases or less than three power supply phases. The wound rotor according to the invention may have more or less than eight reconfigurable magnetic poles, for example four magnetic poles reconfigurable into two poles, or twelve magnetic poles reconfigurable into six poles. In addition, the characteristics of the different variant embodiments of the invention envisaged in this application may be combined to achieve the invention, insofar as these variants are not incompatible with each other.

Claims

Claims

1. Wound rotor assembly (1) and electrical excitation system (2) for the wound rotor (1), the wound rotor (1) comprising a plurality of coils (bl, b2, b3, b4, b5, b6, b7, b8) distributed angularly around the wound rotor (1) and capable of being powered by the excitation system (2) to form magnetic poles (pl, p2, p3, p4, p5, p6, p7, p8), said assembly being characterized in that the wound rotor (1) comprises at least three conductors (A, B, C) electrically connecting the excitation system (2) to at least two angularly adjacent coils (bl, b2) of the plurality of coils, a first of the coils (bl) being connected by one of its ends (11) to a first of the conductors (A) and by the other of its ends (12) to a second of the conductors (B), a second of the coils (b2) being connected by one of its ends (21) to the second conductor (B) and by the other of its ends (22) to a third of the conductors (C),and in that the excitation system (2) is capable of applying a first voltage between the first conductor (A) and the second conductor (B) and a second voltage between the second conductor (B) and the third conductor (C), the first and second voltages being of the same sign or of opposite sign depending on a choice between a first magnetic configuration of the wound rotor (1) and a second magnetic configuration of the wound rotor (1).,

2. An assembly according to claim 1, wherein the plurality of coils (bl, b2, b3, b4, b5, b6, b7, b8) comprises at least one other pair of coils adjacent (b3, b4) to the two adjacent coils (bl, b2) and comprising a third coil (b3) and a fourth coil (b4), the first (bl), second (b2), third (b3) and fourth coils (b4) following each other angularly and having the same winding direction from a first end (11, 21, 31, 41) of the coil to a second end (12, 22, 32, 42) of the coil with respect to a radial direction, - the second end (12) of the first coil (bl) and the first end (21) of the second coil (b2) being connected to the second conductor (B), - the second end (22) of the second coil (b2) and the first end (31) of the third coil (b3) being connected to the third conductor (C), - the second end (32) of the third coil (b3) and the first end (41) of the fourth coil (b4) being connected to the second conductor (B), and - the second end (42) of the fourth coil (b4) and the first end (11) of the first coil (bl) being connected to the first conductor (A).

3. An assembly according to claim 2, wherein the wound rotor (1) comprises an even number of coils (bl, b2, b3, b4, b5, b6, b7, b8) connected to the three conductors (A, B, C), greater than 4, reproducing, following the fourth coil (b4), the connections of the first (bl) and second coils (b2), then depending on the number of coils of the wound rotor (1), of the third (b3) and fourth coils (b4), and so on until reaching the first coil (bl).

4. An assembly according to claim 2 or 3, wherein the wound rotor (1) comprises a coil head guide (9) pressed against an axial end of a cylindrical body of the wound rotor (1) on which the coils (b1, b2, b3, b4, b5, b6, b7, b8) are mounted, the coil head guide (9) comprising pads (92) for winding each first end (61) of one of the coils (b6) and each second end (52) of a coil (b5) adjacent to said coil (b6), the pads (92) being capable of guiding the first (61) and the second end (52) towards a space (90) angularly included between the two coils (b5, b6) for connecting the first end (61) to the second end (52).

5. Assembly according to any one of claims 1 to 4, in which the three conductors (A, B, C) each comprise a conductive ring arranged on one end of a rotating shaft of the wound rotor (1), the excitation system (2) comprising at least one conductive brush per ring, capable of supplying the ring with current during rotation of the wound rotor (1).

6. Assembly according to any one of claims 1 to 5, in which the excitation system (2) comprises a voltage converter stage comprising: - a positive input terminal (H) and a negative input terminal (L) capable of being connected to a DC voltage source, - a first (al), a second (a2) and a third switching arm (a3) ​​connected to the input terminals and each comprising a midpoint connected respectively to the first conductor (A), to the second conductor (B) and to the third conductor (C).

7.

8.

9. An assembly according to claim 6, wherein: - the first switching arm (al) comprises a switch connected between the positive input terminal and its midpoint, and a diode connected between its midpoint and the negative input terminal (L), - the second switching arm (a2) comprises a switch connected between the negative input terminal (L) and its midpoint, and a diode connected between its midpoint and the positive input terminal (H), and - the third switching arm (a3) ​​comprises a first switch connected between the positive input terminal (H) and its midpoint, and a second switch connected between the negative input terminal (L) and its midpoint. Assembly according to claim 7, comprising a control circuit capable of applying: - in the first magnetic configuration of the wound rotor (1), a first non-zero duty cycle aH at the switch of the first arm, a second duty cycle [3L equal to one at the switch of the second arm, a third non-zero duty cycle yH at the first switch of the third arm, and a fourth duty cycle yL less than (1- yH) at the second switch of the third arm, and - in the second magnetic configuration of the wound rotor (1), a first non-zero duty cycle aH at the switch of the first arm, a second duty cycle [3L zero at the switch of the second arm, a third duty cycle yH zero at the first switch of the third arm, and a fourth duty cycle yL equal to one at the second switch of the third arm. Electrical machine comprising an assembly according to any one of claims 1 to 8, a stator (3) with reconfigurable magnetic poles (P1, P2, P3, P4, P5, P6, P7, P8) and means for changing the configuration of the stator (3) between, on the one hand, a third magnetic configuration in which the number of magnetic poles of the stator (3) is identical to the number of magnetic poles of the wound rotor (1) in the first magnetic configuration, and on the other hand, a fourth magnetic configuration in which the number of magnetic poles of the stator (3) is identical to the number of magnetic poles of the wound rotor (1) in the second magnetic configuration, the means for changing the configuration of the stator (3) comprising means for selecting the third or fourth magnetic configuration in function of the first or second magnetic configuration chosen for the wound rotor (1).

10. Electric or hybrid vehicle comprising an electric machine according to claim 9.

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