Electric machine for an aircraft, comprising at least one member for protecting against a short circuit between two stator phases, and protection method

Abstract

The invention relates to an electric machine for an aircraft, comprising a stator (1) comprising at least three phases (10) each comprising a winding (12), a control branch (11) and a neutral branch (13), the neutral branches (13) being connected together at a neutral point (14), the electric machine (3) comprising at least one protection member (5) mounted on the neutral branch (13) of at least one phase (10), each protection member (5) comprising: an inactive state (P1), in which the protection member (5) allows the circulation of the electric current in each phase (10) on which the protection member (5) is mounted, and a protection state (P2), in which the protection member (5) interrupts the circulation of the electric current in each phase (10) on which the protection member (5) is mounted, so as to protect the electric machine in the event of a short circuit (CC).

Description

Electrical machine for aircraft comprising at least one short-circuit protection member between two phases of the stator and protection method

[0001] The present invention relates to the field of electrical machines for aircraft and aims to protect an electrical machine in the event of a short circuit between two phases of a stator of an electrical machine.

[0002] As is known, electrical machines are installed in aircraft, such as helicopters, to provide torque, for example for aircraft propulsion (engine operation), or to generate electrical energy (generator operation). The electrical machines usually used in electrically powered aircraft and those with a hybrid thermal / electric architecture are of the permanent magnet synchronous type due to their high power mass density, which makes it possible to limit the on-board mass of the aircraft.

[0003] It is schematically represented on the an example of a permanent magnet synchronous machine 300 on board a helicopter. In a known manner, a permanent magnet synchronous machine 300 comprises a stator 100, mounted on a casing element of the aircraft, and a rotor 200, mounted to rotate opposite the stator 100. In this example, the permanent magnet synchronous machine 300 is of the radial flux type, that is to say that the rotor 200 has a cylindrical shape and the stator 100 extends in an annular manner externally around the rotor 200.

[0004] In a known manner and with reference to Figures 1 and 2, the rotor 200 comprises permanent magnets and the stator comprises several phases 110, generally three phases. Each phase 110 comprises a winding 130, a control branch 120 and a neutral branch 140. The control branches 120 are connected to a power converter 400, usually an inverter / rectifier, and the neutral branches 140 are connected together at a point, designated neutral point 150. In generator operation, the rotation of the rotor 200 relative to the windings 130 of the stator 100 generates an exciting magnetic flux, at the origin of an alternating electrical voltage between the phases 110.

[0005] In practice, as illustrated in the, a short circuit may occur in the electrical machine 300 when two windings 130 of the stator 100 come into contact at a point, designated the DC short-circuit point. The rotation of the rotor 200 then permanently supplies the circulation of an electric current between the DC short-circuit point and the neutral point 150. The impedance of the windings 130 being usually low, the electric current increases rapidly, which is likely to cause overheating and damage to the components of the stator 100.

[0006] To reduce this risk, it is known from patent application FR3057029A1 to stop the rotation of the rotor of the electrical machine in the event of detection of a short circuit by adding a mechanical decoupling device, implemented for example by clutch or dog clutch. Such a device has a high mass, is expensive and is difficult to integrate.

[0007] Another solution is to size the electrical machine to withstand the short circuit for a sufficient duration, i.e. until the aircraft lands. It has therefore been proposed to reinforce the windings and / or the insulation, which increases the size and mass of the electrical machine and reduces its efficiency undesirably.

[0008] It is also known from patent application FR3091060A1 to take hot air from the thermal power generation system and inject it into the rotor of the electric machine. This makes it possible to reach the Curie temperature of the permanent magnets and thus deactivate their ferromagnetic properties. Such a solution has the disadvantage of exposing the electric machine to undesirably high temperatures.

[0009] It is also known from patent application US20140268460A1 to add a protective element, such as a fuse, between the neutral point and the coil of each phase, or alternatively on the terminal connector side, which blocks the flow of current in the presence of a short circuit. The integration of protective elements into the electrical machine proves difficult in practice, as do their control and maintenance.

[0010] The invention thus aims to protect an electrical machine in the event of a short circuit between two phases of the stator by eliminating at least some of the aforementioned drawbacks. PRESENTATION OF THE INVENTION

[0011] The invention relates to an electrical machine for an aircraft, comprising a stator and a rotor mounted to rotate relative to the stator, said rotor comprising at least one permanent magnet, said stator comprising at least three phases, each phase comprising a winding, a control branch and a neutral branch, said control branches being configured to be connected to a power conversion device, said neutral branches being connected together at a neutral point.

[0012] The invention is remarkable in that the electrical machine comprises at least one protection member mounted on the neutral branch of at least one phase, each protection member comprising: an inactive state, in which the protection member authorizes the flow of electric current in each phase on the neutral branch of which the protection member is mounted, and a protection state, in which the protection member interrupts the flow of electric current in each phase on the neutral branch of which the protection member is mounted, so as to protect the electrical machine in the event of a short circuit.

[0013] By means of the invention, the flow of electric current in one or more phases of the stator is controlled via the protective member, which makes it possible to protect the electrical machine in the event of a short circuit, in particular between two phases of the stator. Each protective member makes it possible to suspend the flow of electric current in one or more given phases, in a targeted, simple and rapid manner, unlike the rotor decoupling device and the hot air circuit of the prior art. Such protective members thus make it possible to interrupt a short circuit between two phases, which ensures effective protection of the stator components from the risk of overheating and damage.

[0014] According to one aspect of the invention, the stator comprises an outer casing and at least a portion of the neutral branch of each phase on which the protection member is mounted extends externally to the outer casing of the stator. Preferably, the neutral point is positioned externally to the outer casing of the stator. This makes it easier to integrate the protection members as well as to control and access them during maintenance.

[0015] According to one aspect of the invention, the neutral branch of each of a plurality of phases is equipped with a protective member. Preferably, N designating the number of phases of the stator, the neutral branch of at least N-1 phases are equipped with a protective member. This makes it possible to protect the electrical machine in a targeted and effective manner regardless of the location of the short-circuit point between two phases. Indeed, the electric current can be interrupted in at least one of the two phases where the short-circuit point is located.

[0016] According to a first aspect of the invention, the electrical machine comprises a plurality of dipole protection members, each protection member being mounted on the neutral branch of a phase. Dipole protection members are advantageously simple and inexpensive.

[0017] According to a second aspect of the invention, the electrical machine comprises a single multi-pole protection member mounted on the neutral branch of each of a plurality of phases, preferably all the phases of the stator. It is specified that the term "multi-pole" qualifies a member comprising more than two electrical poles. Advantageously, a single protection member is sufficient to suspend the flow of electric current in each phase.

[0018] According to a preferred aspect of the invention, each protective member comprises a switch for each phase on which the protective member is mounted. Preferably, the switch is in the form of an electromechanical contactor (EMR), a static contactor (SSR) or a pyrotechnic fuse (PSS). Preferably, the switch is in the form of a solid-state power controller (SSPC). Such a protective member makes it possible to effectively and simply interrupt the electric current in the phase(s) in which it is mounted.

[0019] According to a preferred aspect of the invention, the electrical machine comprises at least one control member configured to activate the protection state of each protection member. The control member ensures the control of the protection members.

[0020] According to a preferred aspect of the invention, the electrical machine comprises at least one member for measuring the electric current flowing in at least one phase of the stator, preferably the sum of the electric currents flowing in all the phases of the stator. Such a measuring member advantageously makes it possible to detect a short circuit and its location at an early stage. A single member for measuring the sum of the electric currents of the phases is advantageously sufficient to monitor all the phases, which limits the space requirement.

[0021] According to one aspect of the invention, the measuring member is in the form of a magnetic current sensor comprising a magnetic loop surrounding the neutral branch or the control branch of at least one phase of the stator, preferably of all the phases of the stator. Such a measuring member has a small footprint, which facilitates its integration into the electrical machine.

[0022] The magnetic current sensor is advantageously of the Hall effect type, offering high measurement precision and simple to integrate.

[0023] Preferably, the measuring device is connected to the control device to allow automatic control of the protection devices, based on monitoring of the electric current in the stator phases.

[0024] The invention also relates to the assembly of an electrical machine as described above and a power conversion device, said power conversion device being connected to the control branch of each phase of the stator. Advantageously, the protection members also make it possible to protect the electrical machine in the event of a short circuit at the power conversion device.

[0025] Preferably, the power conversion device is in the form of an inverter / rectifier.

[0026] According to one aspect of the invention, the power conversion device comprises an outer casing and the neutral point is positioned internally to the outer casing of the power conversion device. This makes it easier to integrate the protection members into the neutral branches and to promote their accessibility in the event of maintenance. Control by means of the control member and the measuring member is also simplified.

[0027] The invention also relates to an aircraft comprising an electrical machine as described above. Preferably, the aircraft is in the form of a helicopter. The protective members advantageously make it possible to protect the electrical machine in the event of a short circuit in flight, which avoids any risk of overheating and damage until the aircraft lands.

[0028] The invention also relates to an aircraft comprising an assembly of an electrical machine and a power conversion device as described previously.

[0029] The invention also relates to a method for protecting an electrical machine as described above, in which each protection member is initially in the inactive state so as to allow the electric current to flow in each phase of the stator, said method comprising: a step of detecting a short circuit between two phases of the stator, and a step of activating the protection state of at least one protection member, in order to interrupt the flow of the electric current in at least one phase of the stator affected by the short circuit, so as to protect the electrical machine.

[0030] The invention also relates to a method for protecting an entire electrical machine and a power conversion device as described above, in which each protection member is initially in the inactive state so as to allow the electric current to flow in each phase of the stator, said method comprising: a step of detecting a short circuit, and a step of activating the protection state of at least one protection member, in order to interrupt the flow of the electric current in at least one phase of the stator affected by the short circuit, so as to protect the electrical machine.

[0031] Such a protection method is advantageously simple and quick to implement, which allows the electrical machine to be protected without delay in the event of a short circuit occurring between two phases of the stator. PRESENTATION OF FIGURES

[0032] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0033] This is a schematic representation of a permanent magnet synchronous machine connected to a power converter according to the prior art.

[0034] This is a schematic representation of a short circuit between two phases of the stator of the permanent magnet synchronous machine of the.

[0035] This is a schematic representation of a permanent magnet synchronous machine connected to a power converter and equipped with protective devices according to one embodiment of the invention.

[0036] This is a schematic representation of the permanent magnet synchronous machine in which the rotor is not shown.

[0037] This is a schematic representation of a method for protecting the permanent magnet synchronous machine during a short circuit between two phases of the stator according to one embodiment of the invention.

[0038] This is a schematic representation of a method for protecting the permanent magnet synchronous machine from a short circuit in the power conversion device.

[0039] This is a schematic representation of a permanent magnet synchronous machine according to another embodiment of the invention, in which the rotor has not been shown.

[0040] This is a schematic representation of a permanent magnet synchronous machine according to another embodiment of the invention in which the rotor has not been shown.

[0041] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention if necessary. DETAILED DESCRIPTION OF THE INVENTION

[0042] The invention relates to an aircraft comprising one or more electrical machines connected to one or more power conversion devices, in order to provide torque, for example for the propulsion of the aircraft (engine operation), or to generate electrical energy (generator operation). The aircraft is in particular of the electric propulsion type or of thermal / electric hybrid architecture. The aircraft is for example in the form of a helicopter.

[0043] It is schematically represented on the example of a permanent magnet synchronous machine 3 on board a helicopter. Such an electric machine advantageously has a high power mass density, which makes it possible to limit the on-board mass of the aircraft. The electric machine is preferably connected to a power conversion device of the inverter / rectifier type 4.

[0044] As described in the preamble and illustrated in the, a permanent magnet synchronous machine 3 comprises a stator 1, mounted on a casing element of the aircraft, and a rotor 2, mounted to rotate relative to the stator 1. In this example, the permanent magnet synchronous machine 3 is of the radial flux type, that is to say that the rotor 2 comprises a cylindrical shape and the stator 1 extends annularly externally around the rotor 2. The invention also applies in particular to a permanent magnet synchronous machine of the reverse radial flux type, in which the stator 1 comprises a cylindrical shape and the rotor 2 extends annularly externally around the stator 1. The invention also applies to a permanent magnet synchronous machine of the axial flux type, in which the stator 1 and the rotor 2 have a cylindrical shape and extend face-to-face in an axial direction.

[0045] As described in the preamble and illustrated in the, the rotor 2 comprises permanent magnets and the stator 1 comprises several phases 10, generally three phases. With reference to the (in which the rotor 2 is not shown for the sake of clarity), each phase 10 comprises a winding 12, a control branch 11 and a neutral branch 13. The control branch 11 and the neutral branch 13 extend respectively at the ends of the winding 12. The control branches 11 are connected to the inverter / rectifier 4 and make it possible to power the electrical machine 3 or to transmit the electrical current produced to the inverter / rectifier 4 depending on whether the operation is motor or generator. The neutral branches 13 are connected together at a point, designated neutral point 14, forming the ground of the electrical machine 3.In generator operation, the rotation of the rotor 2 relative to the windings 10 of the stator 1 generates an exciting magnetic flux, causing an alternating electrical voltage between the phases 10.

[0046] According to the invention and as illustrated in Figures 3 and 4, the electrical machine 3 comprises one or more protection members 5. Each protection member 5 is mounted on one or more phases 10 of the stator, more precisely on the neutral branch 13 of one or more phases 10. Each protection member 5 has an inactive state P1 (see) and a protection state P2 (see). In the inactive state P1, the protection member 5 allows the flow of electric current in each phase 10 on which it is mounted. In the protection state P2, the protection member 5 interrupts the flow of electric current in each phase 10 on which it is mounted. In other words, the protection member 5 makes it possible to electrically connect one or more neutral branches 13 to the neutral point 14 (inactive state P1) or to electrically disconnect the neutral branch(es) 13 from the neutral point 14 (protection state P2).The protective member 5 thus fulfills a switch function.

[0047] The integration of protection members 5 in the electrical machine 3 advantageously makes it possible to protect the electrical machine 3 in the event of a DC short circuit occurring, in particular between two phases 10 of the stator 1 (see), or at the power conversion device 4 (see). More precisely, the activation of the protection state P2 makes it possible to open the neutral point 14 in the event of a short circuit occurring, which avoids the risks of overheating and deterioration of the components of the electrical machine 3 and / or of the power conversion device 4 caused by the short circuit.

[0048] It is specified for all useful purposes that a short circuit between two phases 10 of the stator 1 of the electrical machine 3 designates the contacting of the two phases 10 of the stator 1, for example at the level of the windings 12 in the example of 1a, at a point designated the DC short-circuit point. The rotation of the rotor 2 then permanently supplies the circulation of an electric current between the DC short-circuit point and the neutral point 14. The impedance of the windings 12 being usually low, the electric current increases rapidly and can damage the components of the electrical machine 3. The present invention makes it possible to interrupt the short circuit to avoid any damage by opening the neutral point 14. The invention also makes it possible to protect against other types of short circuit, such as those between the power supply harnesses of two different phases 10 of stator 1, or those between two different power transistors of the inverter / rectifier 4.

[0049] According to one aspect of the invention illustrated in Figures 3, 4 and 8, denoting N the number of phases 10 of the stator 1, a number (N-1) or N of neutral branches 13 are equipped with a protective member 5. This makes it possible to effectively protect the components of the stator 1 regardless of the location of the short circuit by preventing any formation of a current loop. Preferably, (N-1) neutral branches 13 are equipped with a protective member 5 to minimize the mass and the size with optimal protection. Indeed, a short circuit in practice affects two phases 10 of the stator 1, therefore necessarily affects at least one phase 10 equipped with a protective member 5, which is sufficient to interrupt the flow of the electric current at the origin of the short circuit. In the example of figures 3 and 4 of a three-phase electrical machine 10, only two neutral branches 13 are thus equipped with a protection member 5.In the example of the, all the neutral branches 13 are equipped with a protection device 5 to suspend the flow of current in all the phases 10.

[0050] According to one aspect of the invention illustrated in Figures 3, 4 and 8, at least a portion of each neutral branch 13 on which a protection member 5 is mounted extends externally to the outer casing 15 of the stator 1. In other words, the protection members 5, functional elements of the stator 1, physically extend outside the latter. As illustrated in Figures 3, 4 and 8, this is preferably implemented by positioning the neutral point 14 externally to the outer casing 15 of the stator 1. The neutral branches 13 thus comprise at least one external portion extending outside the stator 1 and connected together at the neutral point 14. An external mounting of the protection members 5 is advantageously simple and rapid, without space constraints, and protects the protection members 5 from high temperatures. In addition, such mounting facilitates their accessibility in the event of maintenance.

[0051] Preferably, as illustrated in Figures 3 and 4, the neutral point 14 extends internally to externally 40 of the inverter / rectifier 4. In other words, the neutral point 14, a functional element of the stator 1, physically extends into the inverter / rectifier 4. Each neutral branch 13 thus comprises a first end connected to the winding 12 in the stator 1 of the electrical machine 3 and a second end connected to the neutral point 14 in the inverter / rectifier 4. Between the first end and the second end, each neutral branch 13 comprises an external portion at which the protective member 5 is mounted. In other words, the protective member 5 extends outside the stator 1 and outside the inverter / rectifier 4, for greater ease of access and assembly.

[0052] According to a first aspect of the invention illustrated in Figures 3 and 4, each protection member 5 is in the form of an electric dipole mounted on a single phase 10 of the stator 1. Preferably, the electrical machine 3 comprises N-1 or N protection members 5 each mounted on a phase 10 of the stator 1. Each protection member 5 controls the flow of the electric current in the phase 10 in which it is mounted.

[0053] According to a second aspect of the invention illustrated in the, the electrical machine 3 comprises a single protection member 5 in the form of an electrical multipole. A multipole here designates a member comprising more than two electrical poles. The protection member 5 is mounted in several phases 10 of the stator 1, preferably all of them, and is configured to allow the interruption of each phase 10 on which it is mounted. In the example of the, the protection member 5 is in the form of a hexapole with three interfaces to be mounted on the three phases 10 of the stator 1.

[0054] As illustrated in Figures 3, 4 and 8, each protection member 5 is of the switch type with two different states, namely an inactive state P1 on the one hand and a protection state P2 on the other hand. The protection state P2 is configured to be triggered only when a short circuit occurs, the protection member 5 being otherwise in the inactive state P1.

[0055] According to a preferred aspect, each protection member 5 comprises a switch for each phase 10 on which it is mounted. In the embodiment of Figures 3 and 4, each dipole protection member 5 is in the form of a simple switch. In the embodiment of a multipole protection member 5 of a plurality of phases 10, each multipole protection member 5 comprises a set of switches, one per phase, configured to be triggered simultaneously. According to a preferred aspect, each switch is in the form of a static contactor (“Solid State Relay SSR”), an electromechanical contactor (“Electromechanical Relay EMR”) or a pyrotechnic fuse, also known as a “pyro-fuse”. Preferably, the switch is in the form of a semiconductor power controller (“Solid State Power Controller SSPC”), which advantageously has a reduced mass and volume.Such switches are known to those skilled in the art and are not described further.

[0056] According to one aspect of the invention illustrated schematically in Figures 3 and 4, the electrical machine 3 also comprises a control member 7 configured to control each protection member 5. The control member 7 makes it possible to activate the protection state P2 of each protection member 5, the protection member 5 otherwise being in the inactive state P1. Preferably, the control member 7 ensures identical control of each protection member 5 and is configured to simultaneously activate the protection state P2 of each protection member 5, to protect all the phases 10. Preferably, the control member 7 is in the form of a computer. Preferably, the control member 7 is connected by wire to each protection member 5 so as to transmit a control signal to them.

[0057] According to one aspect of the invention, the electrical machine 3 also comprises one or more measuring members 6 configured to measure a parameter of the electrical machine 3, such as the electric current flowing in the phases 10, the rotation speed of the rotor 2 or the position of the rotor 2. According to a preferred aspect illustrated in FIGS. 3, 4, 7 and 8, the electrical machine 3 comprises one or more measuring members 6 of the electric current flowing in the phases 10 of the stator 1. The measuring member 6 is mounted at the level of the control branch 11 (see 4) or the neutral branch 13 (not shown) of at least one phase 10.

[0058] According to a first aspect illustrated in figures 3 and 4, each phase 10 of the stator 1 is equipped with a measuring member 6. Alternatively, it may be provided that one or more phases 10 could be free of measuring member 6. According to a second aspect illustrated in figures 7 and 8, the electrical machine 3 comprises a single measuring member 6 of the sum of the electric currents circulating in all the phases 10 of the stator 1.

[0059] Preferably, with reference to figures 3, 4, 7 and 8, the measuring member 6 is in the form of a magnetic current sensor comprising a magnetic loop surrounding a branch 11, 13 of a phase 10 of the stator 1 () or a branch 11, 13 of all the phases 10 of the stator 1 (). Preferably, the measuring member 6 is in the form of a Hall effect sensor.

[0060] According to a preferred aspect illustrated in Figures 3 and 4, the control member 7 is connected to each measuring member 6 and is configured to detect the occurrence of a short circuit from the measured parameter, such as the electric current. Preferably, the control member 7 is configured to compare the measurement to a predetermined threshold value, stored for example in a database of the control member 7, in order to detect a threshold exceedance. Preferably, the control of the protection members 5 in the protection state P2 is implemented automatically from the analysis of the measured parameters, which allows rapid and effective protection. Preferably, the parameters are measured continuously or periodically for early and automatic detection of the occurrence of a short circuit. The control of the state of the protection members 5 can alternatively or additionally be implemented manually by an operator.

[0061] With reference to Figures 5 and 6, the invention also relates to a protection method, in which each protection member 5 is initially in the inactive state P1 so as to allow the electric current to flow in each phase 10 of the stator 1 of the electrical machine 3, the method comprising: a step E1 of detecting a DC short circuit between two phases 10 of the stator 1, and a step E2 of activating the protection state P2 of a protection member 5, in order to interrupt the flow of the electric current in a phase 10 of the stator 1 affected by the DC short circuit.

[0062] The protection method is implemented during the operation of the electrical machine 3, the operation being of the motor or generator type. Before the detection step E1, all of the protection members 5 are in the inactive state P1 so as to allow the normal flow of the electric current in each phase 10 of the stator 1.

[0063] With reference to the, the detection step E1 is preferably implemented from one or more measurements of a parameter of the electrical machine 3, for example the electric current flowing in each phase 10 of the stator 1 or the sum of the electric currents flowing in all the phases 10. Other parameters can be measured, such as the rotation speed and the position of the rotor. The measuring members 6, after having acquired these measurements, transmit them to the control member 7 which compares them to a predetermined threshold, an exceeding of the threshold corresponding to a short circuit. Such detection is advantageously automatic and early. Alternatively or additionally, the detection can also be carried out by an operator.

[0064] With reference to 1a, the activation step E2 is implemented after the detection step E1, preferably immediately following this step. According to a first aspect of the invention illustrated in 1a, the control member 7 transmits a control signal to the protection member 5 of a phase 10 affected by the DC short-circuit to activate the protection state P2. The other protection members 5 remain in the inactive state P1. The activation of the protection state P2 of a single protection member 5 located on the short-circuit loop is advantageously sufficient to interrupt the electric current generated by the short-circuit. In the example of 1a, the DC short-circuit affects two phases 10 of the stator 1, one equipped with a protection member 5 and the other not, to minimize the space requirement. The activation step E2 is thus implemented on the single protection member 5 present on the short-circuit loop.In the case of a short circuit affecting two phases 10 each equipped with a protection device 5, the activation step E2 can be implemented on one of the two protection devices 5 only, and is sufficient to properly isolate the faulty phase. In the case of an electrical machine 3 with more than three phases 10, for example five or six, if one phase out of the N phases of the machine is faulty, this also makes it possible to continue operating in a degraded manner on the remaining N-1 phases 10. This makes it possible, with an electrical machine 3 designed to continue operating as soon as the lost phase is properly isolated.

[0065] Preferably, the detection step E1 also makes it possible to determine the phases 10 of the stator 1 affected by the short circuit, namely the two phases where the DC short-circuit point is located in the example of a short circuit between two windings 12. In the example of a measuring device dedicated to each phase 10, this is advantageously carried out from the position of the measuring devices 6 where an abnormal measurement has been measured. An example is illustrated where the short-circuit point appears between two power transistors of the inverter / rectifier 4.

[0066] According to a second aspect of the invention, during the activation step E2, the electric current is interrupted in all the phases 10 equipped with a protection member 5. This advantageously avoids having to locate the DC short circuit and allows protection to be implemented all the more quickly and reliably. In other words, taking the example of 1a, the protection state P2 of each protection member 5 is activated. In the example of 1a, the activation of the protection state P2 of the multipolar protection member 5 alone allows the electric current to be suspended in all the phases 10.

[0067] Following the implementation of the activation step E2, the electric current flowing in the phase 10 of the stator 1 where the protection member 5 is mounted is interrupted. The short-circuit loop is thus opened, which prevents any risk of overheating and damage to the components of the stator 1. Such a solution has the advantage of being able to be implemented early, simply and quickly, which avoids any exposure to unwanted heat of the components. In addition, such a solution has a low cost and is easy to integrate, in particular thanks to the positioning of the neutral point 14 outside the electrical machine 3.

Claims

An electrical machine (3) for an aircraft, comprising a stator (1) and a rotor (2) mounted to rotate freely relative to the stator (1), said rotor (2) comprising at least one permanent magnet, said stator (1) comprising an outer casing (15) and at least three phases (10), each phase (10) comprising a winding (12), a control branch (11) and a neutral branch (13), said control branches (11) being configured to be connected to a power conversion device (4), said neutral branches (13) being connected together at a neutral point (14), said electrical machine (3) being characterized in that it comprises at least one protective device (5) mounted on the neutral branch (13) of at least one phase (10), at least a portion of the neutral branch (13) of each phase (10) on which the protective device (5) is mounted extending externally from the outer casing (15) of the stator (1),each protective device (5) comprising: an inactive state (P1), in which the protective device (5) allows the flow of electric current in each phase (10) on the neutral branch of which the protective device (5) is mounted, and a protected state (P2), in which the protective device (5) interrupts the flow of electric current in each phase (10) on the neutral branch of which the protective device (5) is mounted, so as to protect the electrical machine (3) in the event of a short circuit (SC). Electric machine (3) according to claim 1, wherein the neutral point (14) is positioned externally to the outer casing (15) of the stator (1). Electric machine (3) according to any one of claims 1 and 2, wherein the neutral branch (13) of each of a plurality of phases (10) is equipped with a protective device (5), preferably of at least N-1 phases (10) with N denoting the number of phases (10) of the stator (1). Electric machine (3) according to any one of claims 1 to 3, comprising a plurality of dipolar protective devices (5), each protective device (5) being mounted on the neutral branch (13) of a phase (10). Electric machine (3) according to any one of claims 1 to 3, comprising a single multipole protective device (5) mounted on the neutral branch (13) of each of a plurality of phases (10), preferably of all phases (10) of the stator (1). Electric machine (3) according to any one of claims 1 to 5, wherein each protective device (5) comprises a switch for each phase (10) on which the protective device (5) is mounted, preferably in the form of an electromechanical contactor, a static contactor or a pyrotechnic fuse. Assembly of an electric machine (3) according to any one of claims 1 to 6 and a power conversion device (4), said power conversion device (4) being connected to the control branch (11) of each phase (10) of the stator (1). Assembly according to claim 7, wherein the power conversion device (4) comprises an outer casing (40), the neutral point (14) being positioned internally to the outer casing (40) of the power conversion device (4). Aircraft comprising an electric machine (3) according to any one of claims 1 to 6. A method for protecting an electrical machine (3) according to any one of claims 1 to 6, wherein each protective element (5) is initially in the inactive state (P1) so as to allow electric current to flow in each phase (10) of the stator (1), said method comprising: a step of detecting a short circuit (CC) between two phases (10) of the stator (1), and a step of activating (E2) the protection state (P2) of at least one protective element (5), in order to interrupt the flow of electric current in at least one phase (10) of the stator (1) affected by the short circuit (CC), so as to protect the electrical machine (3).

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