Assembly of an electric motor and a device for controlling the electric motor, and method for controlling such an assembly

Abstract

The invention relates to an assembly (1) of an electric motor (2) for propelling an aircraft and a control device (5), the electric motor (2) comprising a stator (21) and a rotor (22) and at least one cooling channel (CR) configured to be supplied with a heat transfer fluid (F), the control device (5) being configured to issue a control command (01) in order to control the rotation of the rotor (22), the control device (5) also being configured to issue a heating command configured to generate a heating current in the stator (21) in order to heat the heat transfer fluid (F), the heating current comprising a non-zero DC component and a substantially zero quadratic component so as to limit the rotation of the rotor (22) during heating.

Description

Assembly of an electric motor and an electric motor control device, method of controlling such an assembly

[0001] The present invention relates to the field of electric propulsion motors used in the aeronautical field. The invention relates more particularly to the cooling of an electric propulsion motor.

[0002] To reduce the environmental impact of aircraft, it has been proposed to use electric motors to power aircraft. Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This ongoing research and development work focuses in particular on new generations of aircraft engines using electric technologies.

[0006] As is known, an electric motor comprises a rotor rotatably mounted relative to a stator. The stator is powered by a power module, in particular, a direct / alternating type power converter. Such an electric motor is likely to heat up during operation and it is necessary to evacuate the calories from said electric motor in order to allow reliable operation while guaranteeing a long service life.

[0007] As is known, an electric motor has a cooling channel in which a heat transfer fluid, particularly oil, circulates in order to draw calories from the electric motor and ensure its cooling. To allow for optimal cooling, the temperature of the heat transfer fluid must remain within a predetermined temperature range, for example, above 10°C. Indeed, if the temperature of the heat transfer fluid is too low, its viscosity does not allow for optimal cooling.

[0008] In some cold regions of the world, the outside temperature can reach -40°C and the temperature of the heat transfer fluid is not within the predetermined temperature range. To eliminate this disadvantage, it has been proposed in the prior art to mount a heating system between a heat transfer fluid tank and the electric motor in order to heat the heat transfer fluid before it powers the electric motor.

[0009] Such a heating system has many disadvantages, as it increases the space requirement in the vicinity of the electric motor and penalizes the weight of the aircraft. In addition, the presence of a heating system increases the length of the cooling circuit, which requires the use of a heat transfer fluid drive pump, the mass and size of which are high.

[0010] The invention thus aims to eliminate at least some of these drawbacks.

[0011] Document FR3080239A1 relates to a device and method for estimating and correcting a measurement error of a position sensor of a rotor of a rotating electrical machine for an electric vehicle. This document teaches how to preheat a cooling circuit of an electric vehicle. US20070246302A1 teaches a system for preheating the oil of an aircraft oil tank. EP2531328A0 teaches a method for heating robots in cold environments. PRESENTATION OF THE INVENTION

[0012] The invention relates to an assembly of an electric motor for the propulsion of an aircraft, and a device for controlling the electric motor, the electric motor comprising a stator and a rotor mounted to move relative to the stator, the electric motor comprising at least one cooling circuit configured to be supplied by a heat transfer fluid configured to draw calories at least from the stator of the electric motor, the control device being configured to emit a control command configured to generate a control current in the stator of the electric motor in order to control the rotation of the rotor.

[0013] The control device is remarkable in that it is configured to issue a heating command configured to generate a heating current in the stator of the electric motor in order to heat the heat transfer fluid, the heating current comprising a non-zero direct component and a substantially zero quadratic component so as to limit the rotation of the rotor during heating.

[0014] By substantially zero is meant a value less than 5% of the nominal quadratic component during a command to control the rotation of the rotor. Preferably, the electric motor having a predetermined internal friction torque, the quadratic component is less than the internal friction torque so as to prevent any rotation.

[0015] Advantageously, thanks to the invention, the electric motor is powered only with a direct current in order to produce thermal losses without producing torque as a function of the quadratic current. These thermal losses are transmitted to the heat transfer fluid, which allows it to be brought to a current temperature for which its viscosity is optimal for cooling the electric motor. Thanks to the invention, it is not necessary to provide an attached heating device which would increase the mass and size. The electric motor is controlled in a roundabout way to perform a heating function without providing torque.

[0016] Preferably, the stator extends at least partially into the cooling channel. This allows the heat transfer fluid to directly collect the calories generated by the stator and thus increase its temperature. During nominal operation, the heat transfer fluid can also optimally cool the stator.

[0017] Preferably, the heat transfer fluid is oil or glycolated water. The invention is particularly advantageous with these fluids whose viscosity is a function of temperature.

[0018] According to one aspect of the invention, at least one power device is configured to supply at least the stator with the control current from an electrical power source according to the control order, the heat transfer fluid being configured to draw calories from the power device. Advantageously, during heating, calories are supplied, on the one hand, by the electric motor and, on the other hand, by the power device.

[0019] Preferably, the assembly comprises at least one temperature sensor configured to measure a current temperature of the heat transfer fluid, the control device being configured to issue a heating order which is a function of the current temperature. Thus, the heating order and therefore the heating current are configured as a function of the current temperature so as to obtain the desired temperature by regulation. It is thus possible to obtain an optimal temperature of the heat transfer fluid in a given time.

[0020] The invention also relates to an aircraft comprising an assembly as presented previously.

[0021] The invention also relates to a method for controlling an assembly as presented previously, the cooling channel of the electric motor being supplied by the heat transfer fluid, the heat transfer fluid having a current temperature, the rotor being stopped, the method comprising steps consisting of: Issuing a heating order to generate a heating current in the stator of the electric motor in order to heat the heat transfer fluid, the heating current comprising a non-zero direct component and a substantially zero quadratic component so as to limit the rotation of the rotor during heating.

[0022] An electric motor can, for example, heat the heat transfer fluid before it is put into service and the rotor rotates.

[0023] Preferably, the cooling circuit comprises a heat transfer fluid drive pump which is activated during heating in order to collect the calories from the stator with a flow of heat transfer fluid.

[0024] Preferably, the method comprises steps consisting of:Measuring the current temperature of the heat transfer fluid,If the current temperature of the heat transfer fluid is lower than a predetermined threshold temperature, issuing a heating command to generate a heating current in the stator of the electric motor in order to heat the heat transfer fluid, the heating current comprising a non-zero direct component and a substantially zero quadratic component so as to limit the rotation of the rotor during heating.

[0025] Preferably, the method comprises steps consisting of: If the current temperature of the heat transfer fluid is greater than or equal to the predetermined threshold temperature, issuing a control order configured to generate a control current in the stator of the electric motor in order to control the rotation of the rotor.

[0026] Advantageously, if the heat transfer fluid has a current temperature suitable for cooling, the electric motor can be started directly.

[0027] Preferably, the threshold temperature is between 5° and 15°C, preferably around 10°C.

[0028] Preferably, the heating order is determined to increase the current temperature of the heat transfer fluid by at least 1°C / second. PRESENTATION OF FIGURES

[0029] 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.

[0030] This is a schematic representation of an assembly of an electric motor and a device for controlling the electric motor according to one embodiment of the invention.

[0031] This is a schematic representation of an electric motor when receiving a control command.

[0032] This is a schematic representation of an electric motor when receiving a heating command.

[0033] This is a schematic representation of an assembly of an electric motor and a device for controlling the electric motor according to another embodiment of the invention.

[0034] This is a schematic representation of steps in implementing a control method according to the invention.

[0035] 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

[0036] With reference to the, there is shown an assembly 1 according to the invention comprising an electric motor 2 making it possible to participate in the propulsion of an aircraft.

[0037] In a known manner, as illustrated in the, the electric motor 2 comprises a stator 21 and a rotor 22 mounted to move relative to the stator 21. In this example, the stator 21 comprises a plurality of windings which make it possible to generate a rotating magnetic field when the windings are powered. The windings may be concentric or distributed. Preferably, the electric motor 2 comprises several notches in which the windings are mounted.

[0038] The rotor 22 is configured to interact magnetically with the stator 21 in order to drive it in rotation. In this example, the rotor 22 is housed internally to the stator 21 but it goes without saying that the reverse is also possible. The invention applies to any type of electric motor 2, in particular, a permanent magnet synchronous machine or a wound rotor machine. The rotor 22 is secured to one or more propulsion members, for example, a fan or a propeller as illustrated in.

[0039] In this example, still with reference to the, the stator 21, in particular its windings, are powered by an electrical energy source 30 via a power device 3. Preferably, the electric motor 2 is of the three-phase type. Preferably, the electric motor 2 is also configured to operate as a generator in order to produce electrical energy to recharge the electrical energy source 30. In this example, the electrical energy source 30 is a continuous source, for example, an electric battery or a fuel cell.

[0040] The power device 3, also called power electronics, makes it possible to control the currents flowing in the rotor 22 in order to obtain, in particular, the desired rotation speed and / or torque of the rotor 22. The power device 3 makes it possible to ensure a continuous / alternating conversion to power the stator 21. The power device 3 preferably comprises an inverter comprising a plurality of controllable switches in order to control the currents flowing in the stator 21. Such a power device 2 is known to those skilled in the art and will not be presented in more detail.

[0041] Still with reference to the, the assembly 1 comprises a control device 5 configured to issue a control order O1 to the power device 3 in order to generate a control current I1 in the stator 21 of the electric motor 2 to control the rotation of the rotor 22. In this example, the control device 5 indirectly controls the electric motor 2 via the power device 3 but it goes without saying that, in the absence of the power device 3, the control device 5 could directly control the electric motor 2. The control device 5 is in the form of a computer configured to issue a control order O1 and thus determine the control current I1 in the stator 21.

[0042] As is known, a control current I1 is decomposed into three elementary currents for a three-phase electric motor 2. According to the Park transform, the control current I1 can also be decomposed into a direct component I1d and a quadratic component I1q. As is known, the direct component I1d represents the thermal losses while the quadratic component I1q represents the applied torque. The direct component I1d is also used in a speed acceleration mode when the voltage is insufficient.

[0043] To control the torque of the rotor 22 of the electric motor 2, the control current I1 has a quadratic component I1q which is non-zero (nominal quadratic component I1q). Thus, depending on the command from the pilot of the aircraft, the control device 5 modifies the value of the control current I1 to obtain the desired torque of the rotor 22 of the electric motor 2. The direct composite I1d is thus reduced as much as possible to promote the torque.

[0044] The electric motor 2 and the power device 3 generate calories during their operation. Also, as illustrated in , a cooling circuit CR (dashed lines) is provided to draw calories from the electric motor 2 and the power device 3 by circulating a heat transfer fluid F, for example, oil or glycolated water. In this example, the cooling circuit CR comprises a tank 6 in which the heat transfer fluid F is stored and a pump 7 configured to circulate the heat transfer fluid F in the cooling circuit CR. The cooling circuit CR comprises at least one heat exchanger 8 configured to exchange the calories of the heat transfer fluid F with an external fluid Fext, for example, an ambient air flow. During the flight of the aircraft, heat exchanges are important to cool the heat transfer fluid F.

[0045] Preferably, the cooling circuit CR comprises a temperature sensor 9 for measuring the temperature of the heat transfer fluid F. The temperature sensor 9 is preferably positioned close to the tank 6 but it goes without saying that it could be positioned at another point in the cooling circuit CR.

[0046] Thus, during operation of the electric motor 2, the heat transfer fluid F circulates in the cooling circuit CR in a closed loop to take calories from the power device 3 then from the electric motor 2 which are then dissipated in the heat exchanger 8.

[0047] With reference to the, the heat transfer fluid F circulates from upstream to downstream in the cooling circuit CR. In this example, the power device 3 is positioned upstream of the electric motor 2 but it goes without saying that it could be positioned downstream. Similarly, the electric motor 2 and the power device 3 could be supplied in parallel with heat transfer fluid F.

[0048] According to the invention, with reference to the, the electric motor 2 comprises at least one cooling channel 23 configured to be supplied by the heat transfer fluid F of the cooling circuit CR. Similarly, the power device 3 comprises at least one cooling channel 33 configured to be supplied by the heat transfer fluid F of the cooling circuit CR.

[0049] In this embodiment, the stator 21 extends at least partially into the cooling channel 23 of the electric motor 2. This advantageously makes it possible to collect the calories generated by the stator 21 during its power supply. Preferably, the stator 21 and the rotor 22 are bathed in the heat transfer fluid F to allow optimal cooling. In particular, the windings of the stator 21 are bathed in the heat transfer fluid F. Preferably, the notches of the electric motor 2 are bathed in the heat transfer fluid F.

[0050] Similarly, the power device 3 comprises a plurality of components extending into the cooling channel 33 of the power device 3. This advantageously makes it possible to collect the calories generated by the power device 3 when powering the stator 21 as will be presented later. Preferably, one or more components comprise fins to improve the heat exchanges with the heat transfer fluid F circulating in the cooling channel 33 of the power device 3, in particular, a plurality of tubular fins.

[0051] According to the invention, the electric motor 2 is configured to heat the heat transfer fluid F prior to the operational commissioning of the electric motor 2, that is to say, prior to the rotation of the rotor 22.

[0052] According to the invention, with reference to the, the control device 5 is configured to emit a heating order O2 configured to generate a heating current I2 in the stator 21 of the electric motor 2 in order to heat the heat transfer fluid F located in the cooling channel 23 of the electric motor 2. The heating current I2 comprises a non-zero direct component I2d and a substantially zero quadratic component I2q so as to limit the rotation of the rotor 22 during heating.

[0053] By substantially zero, it is meant that the quadratic component I2q is insufficient to rotate the rotor 22 in order to create a propulsion force. Preferably, the electric motor 2 having a predetermined internal friction torque, the quadratic component I2q is less than the internal friction torque so as to prevent any rotation. According to a preferred aspect, the quadratic component I2q is less than 5% of the nominal quadratic component I1q determined when controlling the electric motor 2.

[0054] Thus, a heating order O2 determines a heating current I2 which generates very predominantly thermal losses by Joule effect in the stator 21 of the electric motor 2 without rotating the rotor 22 and generating a torque. This is very advantageous given that it makes it possible to heat the heat transfer fluid F in a preliminary manner to the operational commissioning. The direct component I2d makes it possible to generate electrical losses and therefore thermal energy by Joule effect. Thus, instead of minimizing thermal losses and maximizing the torque when the electric motor 2 is in operational service, the present invention aims to achieve heating, preliminary to the operational service in which the thermal losses are maximized and the torque minimized.

[0055] In the example of the, the power device 3 makes it possible to power a stator 21 comprising a single stator star in order to drive the rotor 22 in rotation. Nevertheless, the invention also applies to a power device 3 comprising a first power module 31 and a second power module 32 which are independent and, preferably, segregated in order to increase redundancy and reliability as illustrated in the. Such power modules 31, 32 are advantageous when the stator 21 comprises several stator stars 21a, 21b which can be powered independently. As illustrated in the, the cooling circuit CR makes it possible to cool the two power modules 31, 32 in parallel.

[0056] An example of implementation of a control method according to the invention will now be presented with reference to the.

[0057] In this example, the aircraft is stored on the ground at an airport in a cold region, for example at -40°C, and is to perform a flight (operational service). Due to the outside temperatures, the current temperature Tf of the heat transfer fluid F is lower than a predetermined threshold temperature Ts. Preferably, the threshold temperature Ts is between 5°C and 15°C, preferably of the order of 10°C.

[0058] Thanks to the control method according to the invention, the current temperature Tf of the heat transfer fluid F will be increased to reach the threshold temperature Ts and thus allow optimal collection of calories when the electric motor 2 is in operational operation, that is to say, with rotation of its rotor 22. Indeed, as explained previously, if the current temperature Tf of the heat transfer fluid F is too low, its viscosity does not allow optimal cooling.

[0059] With reference to the, the pump 7 is activated so as to circulate the heat transfer fluid F in the cooling circuit CR. In the initial state, the electric motor 2 is not controlled and the power device 3 does not supply current to the stator 21.

[0060] The method comprises a step E1 consisting of measuring the current temperature Tf of the heat transfer fluid F, in particular, by means of the temperature sensor 9.

[0061] If the current temperature Tf of the heat transfer fluid F is lower than the threshold temperature Ts, the method then comprises a step E2 consisting of issuing a heating order O2 to generate a heating current I2 in the stator 21 of the electric motor 2 in order to heat the heat transfer fluid F. In practice, the temperature sensor 9 provides the current temperature Tf of the heat transfer fluid F to the control device 5 which issues a heating order O2 as illustrated in. This heating order O2 modifies the position of the switches of the power device 3 in order to generate a heating current I2 comprising a non-zero direct component I2d and a substantially zero quadratic component I2q so as to limit the rotation of the rotor 22 during heating. The quadratic component I2q is so low that the rotation of the rotor 22 is zero or almost zero, which avoids generating thrust while the aircraft is in the heating phase.

[0062] The direct component I2d (non-zero) of the heating current I2 generates heating by Joule effect of the stator 21 which transmits its calories to the heat transfer fluid F located in the cooling channel 23 in contact with the windings of the stator 21. In this example, the direct component I2d has a constant amplitude greater than 200A peak, preferably of the order of 300A peak. Preferably, its frequency is low of the order of 10 Hz. This advantageously makes it possible to generate thermal losses of 16 kW. Thus, the current is converted mainly into thermal losses.

[0063] As the pump 7 is activated, the heat transfer fluid F gradually heats up in the cooling circuit CR in contact with the stator 21. Since the aircraft is on the ground, the heat exchanger 8 has a very low external fluid flow rate Fext. As a result, the heat exchanger 8 only slightly lowers the current temperature Tf of the heat transfer fluid F, in particular, less than the electric motor 2 increases its current temperature Tf.

[0064] Unlike conventional operation in which the heat transfer fluid F is used to dissipate calories, the heat transfer fluid F is used to collect calories and increase the temperature.

[0065] Preferably, the method comprises a step E3 consisting of monitoring the current temperature Tf of the heat transfer fluid F and adapting the direct component I2d of the heating current I2 in order to obtain the desired temperature rise. Preferably, the heating order O2 is determined to increase the current temperature Tf of the heat transfer fluid F by at least 1°C / second. This allows rapid heating to be achieved and avoids delaying the flight of the aircraft. In this example, the current temperature Tf is increased by 30°C in 30 seconds.

[0066] Still with reference to the, when the current temperature Tf of the heat transfer fluid F is greater than or equal to the threshold temperature Ts, for example, 10°C. The method comprises a step consisting of transmitting E4 a control order O1 configured to generate a control current I1 in the stator 21 of the electric motor 2 in order to control the rotation of the rotor 22 (). Preferably, the control device 5 transmits a control order O1 determining a control current I1 whose quadratic component Iq1 is non-zero so as to allow the rotation of the rotor 22.

[0067] By means of the invention, the current temperature Tf of the heat transfer fluid F is gradually increased in order to reach the threshold temperature Ts. At such a threshold temperature Ts, the heat transfer fluid F has optimal characteristics for dissipating calories, in particular, in terms of viscosity. The rotor 22 can then be set into rotation and the heat transfer fluid F makes it possible to collect the calories induced by the rotation both in the electric motor 2 and in the power device 3. The control order O1 can then be issued so that the aircraft can carry out its flight mission.

[0068] Advantageously, if the current temperature Tf of the heat transfer fluid T is greater than or equal to the threshold temperature Ts prior to starting the electric motor 2, no O2 heating order is issued by the control device 5 and the electric motor 2 can be started directly.

[0069] Thanks to the invention, an electric motor 2 can be started safely and reliably without adding additional equipment which increases the mass and size in the aircraft. The control device 5 advantageously makes it possible to provide an O2 heating command which allows the electric motor 2 to behave like an electric heater without generating torque.

Claims

Assembly (1) of an electric motor (2) for the propulsion of an aircraft, and a control device (5) of the electric motor (2),The electric motor (2) comprising a stator (21) and a rotor (22) mounted movably relative to the stator (21), the electric motor (2) comprising at least one cooling circuit (CR) configured to be supplied by a heat transfer fluid (F) configured to draw calories at least from the stator (21) of the electric motor (2),The control device (5) being configured to emit a control command (O1) configured to generate a control current (I1) in the stator (21) of the electric motor (2) in order to control the rotation of the rotor (22),characterized by the fact thatthe control device (5) is configured toMeasure the current temperature (Tf) of the heat transfer fluid (F),If the current temperature (Tf) of the heat transfer fluid (F) is lower than a predetermined threshold temperature (Ts) included between 5° and 15°C,issuing a heating order (O2) configured to generate a heating current (I2) in the stator (21) of the electric motor (2) in order to heat the heat transfer fluid (F), the heating current (I2) comprising a non-zero direct component (I2d) and a substantially zero quadratic component (I2q) so as to limit the rotation of the rotor (22) during heating. If the current temperature (Tf) of the heat transfer fluid (F) is greater than or equal to the predetermined threshold temperature (Ts), issuing (E3) a control order (O1) configured to generate a control current (I1) in the stator (21) of the electric motor (2) in order to control the rotation of the rotor (22)., Assembly (1) according to claim 1, wherein the stator (21) extends at least partially into the cooling channel (23). Assembly (1) according to one of claims 1 to 2, in which the heat transfer fluid (F) is oil or glycolated water. Assembly (1) according to one of claims 1 to 3, comprising at least one power device (3) configured to supply at least the stator (21) with the control current (I1) from an electrical power source (30) as a function of the control order (O1), the heat transfer fluid (F) being configured to draw calories from the power device (3). Assembly (1) according to one of claims 1 to 4, comprising at least one temperature sensor (9) configured to measure a current temperature (Tf) of the heat transfer fluid (F), the control device (5) being configured to emit a heating order (O2) which is a function of the current temperature (Tf). Aircraft comprising an assembly (1) according to one of claims 1 to 5. Method for controlling an assembly (1) according to one of claims 1 to 5, the cooling channel (23) of the electric motor (2) being supplied by the heat transfer fluid (F), the heat transfer fluid (F) having a current temperature (Tf), the rotor (22) being stopped, the method comprising steps consisting of:Measuring (E1) the current temperature (Tf) of the heat transfer fluid (F),If the current temperature (Tf) of the heat transfer fluid (F) is lower than a predetermined threshold temperature (Ts) between 5° and 15°C, issuing (E2) a heating order (O2) to generate a heating current (I2) in the stator (21) of the electric motor (2) in order to heat the heat transfer fluid (F), the heating current (I2) comprising a non-zero direct component (I2d) and a substantially zero quadratic component (I2q) so as to limit the rotation of the rotor (22) when heating,If the current temperature (Tf) of the heat transfer fluid (F) is greater than or equal to the predetermined threshold temperature (Ts), issue (E3) a control order (O1) configured to generate a control current (I1) in the stator (21) of the electric motor (2) in order to control the rotation of the rotor (22)., Method according to claim 7, in which the threshold temperature (Ts) is of the order of 10°C. Method according to one of claims 7 to 8, in which the heating order (O2) is determined to increase the current temperature (Tf) of the heat transfer fluid (F) by at least 1°C / second.

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