Turbomachine comprising a correction module for correcting a torsion mode for a transmission line connected to an electric machine, and associated method

Abstract

An aircraft turbomachine (T) comprising an electric machine 1 connected to a transmission line 2 and a control device 3 to determine the current in the electric machine so that it provides an electric

Description

TITLE OF THE INVENTION: Turbomachine comprising a correction module for correcting a torsion mode for a transmission line connected to an electric machine, and associated method TECHNICAL FIELD

[001] This invention relates to the field of the electric machines on board a turbomachine of an aircraft in order to achieve a hybrid propulsion. The invention is particularly advantageous for an electric machine connected to a propulsion shaft of an aircraft turbomachine via a transmission line, this electric machine being configured to operate in a motor mode to drive in rotation the propulsion shaft or in a generator mode to generate electrical energy.

[002] The climate change is a major concern for many legislative and regulatory members around the world. Various restrictions on carbon emissions have been, are being or will be adopted by different countries. In particular, an ambitious standard applies both to new types of aircrafts and to those already in circulation, requiring the implementation of technological solutions so as to bring them into line with current regulations. For several years now, the civil aviation has been working to help combat climate change.

[003] The technological research efforts have already led to significant improvements in the environmental performance of the aircrafts. The Applicant takes into consideration the factors impacting all phases of design and development to obtain aeronautical elements and products that consume less energy, are more environmentally friendly and whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of the aircrafts.

[004] Consequently, the Applicant is constantly working to reduce its negative impact on the climate by employing methods and using development and manufacturing methods that are virtuous and minimise greenhouse gas emissions as much as possible in order to reduce the environmental footprint of its business.

[005] This sustained research and development work is focused on new generations of aircraft engines, making aircraft lighter, particularly through the materials used and lighter on-board equipment, developing the use of electrical technologies for propulsion and, as an essential complement to technological progress, aeronautical biofuels.

[006] It is known in the prior art to mount an electric machine on a propulsion shaft of an aircraft turbomachine, for example a fan shaft, in order to obtain a hybrid turbomachine. In particular, the electric machine is configured to operate in a generator mode so as to take up mechanical power from the propulsion shaft in order to generate electrical power. The electric machine is also configured to operate in a motor mode so as to provide mechanical power to the propulsion shaft by taking up electrical power, for example, from an electrical battery.

[007] With reference to Figure 1, in order to facilitate the integration of the electric machine 1, it was proposed to connect it to a propulsion shaft of the turbomachine Ahp via a transmission line 2 comprising an internal gear box 21 (IGB), a radial drive shaft 22 (RDS) and an accessory gear box 23 (AGB). In a known way, the electric machine 1 comprises a stator 11 and a rotor 12 configured to interact magnetically with the stator 11. The aircraft turbomachine 1 comprises a control device 103 configured to receive a setpoint torque TRQcons and to determine the currents circulating in the stator 11 so that the rotor 12 supplies an electric machine torque in accordance with the setpoint torque TRQcons.

[008] In this example, the currents circulating in the stator are determined by measuring the current values of said currents.

[009] In practice, when the transmission line 2 is operating in motor or generator mode, a torsion mode Mt is likely to occur in the transmission line 2. A torsion mode Mt corresponds in particular to an oscillation of torque and speed at a torsion frequency. The torsion mode Mt may manifest itself, for example, in the form of a torsion of the radial drive shaft 22, i.e. an angular offset between two longitudinal portions of the radial drive shaft 22.

[010] Such a torsion mode Mt affects the performance of the transmission line 2 and can induce the excitations or resonances which lead to premature wear of the elements of the transmission line 2 but also to wear of the electric machine 1.

[011] An immediate solution would be to increase the rigidity of the transmission line 2 to increase the frequency of the mode while increasing the damping of the chain so as to reduce the sensitivity of the torsion mode Mt. Such a solution is not feasible, as it would increase the mass of the transmission line 2 and its overall dimensions, which would partly ruin the advantages associated with hybridisation.

[012] Another known solution is to add a mechanical or hydraulic damper to attenuate the excitation of the torsion mode Mt. This solution has the disadvantage of increasing the on-board weight. Moreover, a mechanical damper has a limited service life. For example, it must not be used in steady regime.

[013] In addition, these solutions do not necessarily allow the torsion mode Mt to be attenuated independently of the type of electric machine 1, in particular, without access to the internal measurements of the electric machine 1 and without recourse to a unit for observing the currents of the electric machine 1, which is expensive and complex to implement due to overall dimension and mass constraints. PRESENTATION OF THE INVENTION

[014] The invention relates to an aircraft turbomachine comprising at least one propulsion shaft and an electric machine connected to the propulsion shaft by a transmission line configured to transmit a mechanical torque between the propulsion shaft and the electric machine, the electric machine being configured to receive a setpoint torque, the transmission line being subjected to a torsion mode having an estimated torsion frequency, the electric machine comprising a stator and a rotor configured to interact magnetically with the stator, the electric machine being configured to operate, on the one hand, in a generator mode to take mechanical power from the rotor to generate electrical power and to operate, on the other hand, in a motor mode so as to inject mechanical power from an electrical network and drive the rotor.

[015] The aircraft turbomachine is remarkable in that it comprises a control device configured to determine the currents circulating in the stator so that the rotor supplies an electric machine torque in accordance with a control torque, the control device comprising a correction module configured to attenuate an excitation of the torsion mode of the transmission line, the control device being configured to calculate the control torque from the setpoint torque and a correction torque.

[016] The correction module is configured to calculate the correction torque from a rotation speed of the propulsion shaft over a frequency range encompassing the estimated torsion frequency, referred to as the "monitoring range".

[017] Thus, thanks to the invention, the torsion mode for the transmission line is dynamically corrected during both transient regime and steady regime, which increases the service life of the electric machine and of the transmission line by reducing the torque variations of the electric machine. This type of correction is also advantageous when the electric machine is operating in motor mode or generator mode. The transitions between the two modes are also made easier. In steady regime, the correction is small, which saves the electric machine and prevents it from being used unnecessarily. Moreover, because the damping is provided by software, there is no need to add a mechanical part whose mass would be detrimental and would need to be replaced.

[018] Advantageously, there is no need to add new sensors to the electric machine or to access measurements from said electric machine, which facilitates the integration. By measuring the speed of rotation of the propulsion shaft, the correction module is advantageously independent of the electric machine. This means that any type of electric machine can be used, making logistics easier and reducing costs. The rotational speed of the propulsion shaft is advantageously measured reliably over the entire operating range of the aircraft turbomachine. In addition, the mechanical excitation can be measured at a location further away from the electric machine. This allows you to see how the mechanical chain reacts to the pick-up / injection of the most powerful equipment positioned on the accessory gear box (when the latter is present).

[019] In one aspect, the transmission line comprises at least one radial drive shaft and an accessory gear box. Such a transmission line is particularly efficient but subject to a torsion mode.

[020] In one aspect, the transmission line comprises at least one internal gear box. In one aspect, the transmission line comprises at least one gear box.

[021] In one aspect, the turbomachine is hybrid and comprises a combustion chamber to generate an exhaust flow to drive the propulsion shaft in rotation.

[022] In one aspect, the speed of the propulsion shaft being connected to the speed of the electric machine by a predetermined speed ratio, the correction module comprises a conversion unit configured to convert the speed of the propulsion shaft into an electric machine temporal speed, referred to as the "temporal measurement". This allows to switch from the frame of reference of the drive shaft to the frame of reference of the electric machine in order to achieve an optimum damping.

[023] In one aspect, the correction module comprises a gain operator having a gain for multiplying the time measurement. This allows to adjust the speed of correction of the torsion mode.

[024] In one aspect, the correction module comprises a high-pass filter for cutting off the frequencies below the monitoring range. Preferably, the high-pass filter has a cut-off frequency corresponding to a lower limit Fte1 of the monitoring range, the lower limit being between Fte / 3 and Fte / 2, Fte being the estimated torsion frequency.

[025] In one aspect, the correction module comprises a low-pass filter to cutting off the frequencies above the monitoring range and thus eliminate all high-frequency noise to improve the correction.

[026] According to one aspect, the correction module comprises a saturator to limit the correction torque and thus protect the mechanical chain against the injection of an undesired transient over-torque.

[027] Preferably, the monitoring range comprises a width of between 10 Hz and 50 Hz. This reduced width means that the actual torsion frequency can be precisely targeted, while still allowing for permissible variation due to wear and the particular characteristics of each transmission line.

[028] In one aspect, the control device is configured to determine control currents for the electric machine from the control torque.

[029] Also presented is a method for correcting the torsion mode for the transmission line of the aircraft turbomachine as presented previously, the electric machine receiving a setpoint torque, the method comprising steps consisting in: - Calculating a correction torque from the rotational speed of the propulsion shaft over a frequency range encompassing the estimated torsion frequency, referred to as the "monitoring range", and - Calculating a control torque from the setpoint torque and the correction torque.

[030] According to another aspect, the invention relates to a computer program product comprising code instructions which, when these code instructions are executed by a processing unit, cause said processing unit to implement such a torsion mode correction method. PRESENTATION OF FIGURES

[031] The invention will be better understood on reading the following description, given by way of example, with reference to the following figures, given by way of non-limiting examples, wherein identical references are given to similar objects.

[032] Figure 1 is a schematic representation of an aircraft turbomachine according to the prior art.

[033] Figure 2 is a schematic representation of an aircraft turbomachine according to one embodiment of the invention.

[034] Figure 3 is a schematic representation of the control device for controlling the electric machine comprising a correction module.

[035] Figure 4 is a schematic representation of the correction module.

[036] Figure 5 is a schematic representation of a measurement of the torsion torque at the level of the adapter box, in time (curve 5a) and in frequency (curve 5b), when the correction is inactive (A).

[037] Figure 6 is a schematic representation of the measurement of the torsion torque at the level of the adapter box, in time (curve 6a) and in frequency (curve 6b), when the correction is active (B).

[038] Figure 7 is a schematic representation of the variations in mechanical torque at the level of a shaft of the electric machine when the correction is inactive (A) and active (B) for a first torque setpoint.

[039] Figure 8 is a schematic representation of the mechanical torque variations at the level of a shaft of the electric machine when the correction is inactive (A) and active (B) for a second torque setpoint.

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

[041] Figure 2 shows an aircraft turbomachine T comprising a low-pressure compressor 101, a high-pressure compressor 102, a high-pressure turbine 103 and a low-pressure turbine 104. A low-pressure shaft Abp connects the low-pressure compressor 101 to the low-pressure turbine 104. A high-pressure shaft Ahp connects the high-pressure compressor 102 to the high-pressure turbine 103. A fan 100 is mounted secured to the low-pressure shaft Abp. The aircraft turbomachine T comprises a combustion chamber (not shown) for consuming a mixture of fuel and a flow of pressurised air accelerated by the compressors 101, 102. An exhaust flow is used to drive in rotation the turbines 103, 104. The high-pressure shaft Ahp and the low-pressure shaft Abp are both propulsion shafts, since they are the main shafts involved in the propulsion. The architecture of such an aircraft turbomachine T is known to the person skilled in the art and will not be presented in greater detail.

[042] In a known way, with reference to Figure 2, the aircraft turbomachine T comprises a computer 5 configured to measure a high-pressure rotational speed Nhp of the high-pressure shaft Ahp and a low-pressure rotational speed Nbp of the high-pressure shaft Ahp. Advantageously, the rotational speeds Nhp, Nbp are measured reliably over the entire operating range of the aircraft turbomachine T.

[043] In this example, the aircraft turbomachine T is hybrid and comprises an electric machine 1 connected to the high-pressure shaft Ahp by a transmission line 2 configured to transmit a mechanical torque between the high-pressure shaft Ahp and the electric machine 1. However, it goes without saying that the invention also applies to an electric machine 1 connected to the low-pressure shaft Abp by a transmission line 2 or directly to the low-pressure shaft Abp.

[044] In this example, with reference to Figure 2, the transmission line 2 preferably comprises in succession from the high-pressure shaft Ahp to the electric machine 1: - an Internal Gear Box 21 (IGB), - a Radial Drive Shaft 22 (RDS), - an Accessory Gear Box (AGB) 23, and - a Gearbox 24 (GBX).

[045] Preferably, the computer 5 is connected to one or more speed sensors mounted on the aircraft turbomachine T, in particular, connected to the accessory gear box 23.

[046] The internal gear box 21 comprises gears and is housed as close as possible to the high-pressure shaft Ahp to allow power to be transmitted / received. The radial drive shaft 22 preferably extends into a radial arm of the turbomachine T in order to pass through a duct of air accelerated by the fan 100. The radial drive shaft 22 has a degree of flexibility and is particularly sensitive to a torsion mode Mt. The accessory gear box 23 comprises a plurality of gears to accommodate different accessories such as a starter, a lubrication device, etc.

[047] In this example, optionally, the transmission line 2 comprises a gear box 24 configured to adapt the speed output from the accessory gear box 23 so as to allow the electric machine 1 to generate electrical energy with a high efficiency. Preferably, the gearbox 24 comprises a device for measuring the torque of the transmission line 2, in particular a torque meter.

[048] It goes without saying that the transmission line 2 could have a different structure.

[049] As mentioned previously, the transmission line 2 is subjected to a torsion mode Mt having an actual torsion frequency Ftr which is not necessarily precisely known. The actual torsion frequency Ftr varies between each aircraft turbomachine T and between each transmission line 2 as a result of the different settings, wear and loading level of the transmission line 2. The actual torsion frequency Ftr thus changes as a function of time and conditions.

[050] The transmission line 2 can be modelled by a damping system connecting, on the one hand, the electric machine 1 with a high rigidity and, on the other hand, the high-pressure shaft Ahp. The damping system comprises a torsion stiffness in two degrees of freedom in the reference frame of the electric machine 1. The torsion stiffness is advantageously defined in a plane orthogonal to the axis of the electric machine 1.

[051] As will be shown later, the correction is optimal in this case given that the inertia ratio of the electric machine 1 on the high-pressure shaft Ahp is low, for example of the order of 1 / 40.

[052] The torsion mode Mt may manifest itself, for example, in the form of a torsion of the radial drive shaft 22, i.e. an angular offset between two longitudinal portions of the radial drive shaft 22.

[053] By way of example, with reference to Figure 5, there is a measurement of the mechanical torque received by the gearbox 24 in the absence of time (curve 5a) and frequency (curve 5b) correction. In this example, the actual torsion frequency Ftr is of the order of 25 Hz.

[054] As will be shown later, an estimated torsion frequency Fte is determined by calculation, in particular from a mathematical model of the transmission line 2, for example by simulation or feedback.

[055] Advantageously, a frequency range encompassing the estimated torsion frequency Fte, referred to as the "monitoring range Ps", is determined from the estimated torsion frequency Fte. This monitoring range Ps comprises a lower limit Fte1 and an upper limit Fte2. The monitoring range Ps is preferably centred on the estimated torsion frequency Fte but could be offset from said estimated torsion frequency Fte.

[056] Preferably, the monitoring range Ps has a width, i.e. a distance between its lower limit Fte1 and its upper limit Fte2, of between 10 Hz and 50 Hz. Such a monitoring range Ps is wide enough to encompass the possible variations in the estimated torsion frequency Fte and narrow enough to avoid encompassing undesirable frequencies. Preferably, the lower limit Fte1 is between Fte / 3 and Fte / 2. Preferably, the upper limit Fte2 is between 2*Fte and 3*Fte.

[057] In this example, the estimated torsion frequency Fte was measured at 23 Hz and the monitoring range Ps is equal to [10 Hz; 50 Hz] and is therefore 40 Hz wide.

[058] With reference to Figure 2, the electric machine 1 comprises a stator 11 mounted stationary in the turbomachine T and a rotor 12 connected to the transmission line 2, in particular to the gearbox 24. If there is no gearbox 24, the rotor 12 is connected directly to the accessory gear box 23. The rotor 12 is mounted in a rotative manner relative to the stator 11 along an electric machine axis X. The rotor 12 is configured to interact magnetically with the stator 11. The electric machine 1 is, for example, a permanent magnet synchronous machine (PMSM). These magnets are mounted on the surface of the rotor 12, for example. The electric machine 1 could also be of the wound rotor type.

[059] Preferably, the electric machine 1 does not have a mechanical damper, as the damping provided by the latter is not optimal and is difficult to integrate. Moreover, a mechanical damper of this type wears out quickly and needs to be changed periodically. It is also an additional on-board weight.

[060] The electric machine 1 is configured, on the one hand, to operate in a generator mode so as to take up mechanical power from the rotor 12 (in this example from the high-pressure shaft Ahp) to generate electrical power and, on the other hand, to operate in a motor mode so as to inject electrical power to generate mechanical power and drive the rotor 12 and the high-pressure shaft Ahp.

[061] Still referring to Figure 2, the aircraft turbomachine T also comprises a control device 3 configured to receive a setpoint torque TRQcons. The control device 3 for controlling the electric machine 2 may be adjacent to it or offset from it. The setpoint torque TRQcons is preferably determined by a computer 5 in the turbomachine T or by a computer in the aircraft, for example in order to achieve the chosen hybridization ratio.

[062] An example of embodiment of a control device 3 is shown in Figure 3. The control device 3 is configured to determine the currents circulating in the stator 11 so that the rotor 12 provides an electric machine torque TRQ in accordance with a control torque TRQ*. The control device 3 comprises a unit 31 for determining a setpoint inverse current Iq* from the control torque TRQ*. The control device 3 also comprises a unit 32 for determining a direct setpoint current Id*. The setpoint currents Iq*, Id* are converted into setpoint voltages Vq*, Vd* by a conversion unit 33 after integration of the setpoint currents Iq*, Id* by operators PI (Proportional Integral) from current measurements of the currents Iq, Id circulating in the stator 11 of the electric machine 1.

[063] In this example, currents labc are measured at the level of the stator 11 of the electric machine 1 and are converted vectorially into a direct current Id and a reverse current Iq by knowing an angular position 0 of the rotor 12 relative to the stator 11. The electric machine 1 is controlled via a vector control dq as shown in Figure 3.

[064] The conversion unit 33 determines the setpoint voltages Vq*, Vd* by knowing the speed w of the rotor 12 relative to the stator 11 in order to carry out a defluxing. Preferably, the speed w of the rotor 12 is obtained by integrating the angular position 0.

[065] According to one aspect, the angular position 0 of the rotor 12 with respect to the stator 11 is obtained by a monitoring unit 36 which may be connected to an angular sensor 37 or to an observation unit (not shown) which allows to determine the angular position 0 from the measurement of the control currents labc.

[066] The setpoint voltages Vq*, Vd* supplied by the conversion unit 33 are transformed into the control voltage Vabc* by a dq / abc converter and then processed by a control unit 34 in order to supply a control parameter setting (PWM signal for example) to an inverter 35 supplying the electric machine 1, in particular its stator 11.

[067] The general structure of a control device 3 is known to the person skilled in the art and will not be presented in greater detail. In this example, the angular position 0 of the rotor 12 and the speed w of the rotor 12 are obtained from the monitoring unit 36 and / or the angular sensor 37, which can either make a direct measurement or implement an estimator.

[068] The control device 3 comprises a correction module 4 configured to correct the torsion mode Mt (i.e. to attenuate the excitation of the torsion mode Mt) of the transmission line 2. Advantageously, this allows to reduce the variations in the torque of the electric machine 1, making the hybridisation of the turbomachine T possible, and to prevent breakage of the mechanical chain and increase its service life. The control device 3 is configured to calculate the control torque TRQ* from the setpoint torque TRQcons and a correction torque TRQcorr.

[069] According to the invention, the correction module 4 is configured to calculate the correction torque TRQcorr from the high-pressure rotation speed Nhp of the high-pressure propulsion shaft Ahp over a frequency range encompassing the estimated torsion frequency Fte, referred to as the "monitoring range Ps".

[070] In this way, the correction torque TRQcorr is determined indirectly without requiring direct access to a speed measurement of the electric machine 1. This allows to correct the torsion torque Mt for any type of electric machine 1.

[071] In this example, with reference to Figure 3, the control device 3 comprises a subtractor 38 configured to determine the control torque TRQ* by subtracting the correction torque TRQcorr from the setpoint torque TRQcons. The correction module 4 allows to measure the variations induced by the torsion mode Mt in order to determine a correction torque TRQcorr which modifies the setpoint torque TRQcons. In other words, the correction module 4 implements an active and dynamic compensation in order to control the electric machine 1 taking into account the torsion mode Mt to attenuate the torque / speed oscillations. The correction torque TRQcorr is injected in phase opposition to the torque and speed disturbance associated with the torsion mode Mt, which has a damping effect.

[072] Figure 4 shows a schematic illustration of a correction module 4. In this example, the correction module 4 successively comprises a conversion unit 40, a low-pass filter 41, a high-pass filter 42, a gain operator 43 with a gain Kp and a saturator 44.

[073] The high-pressure speed Nhp of the high-pressure propulsion shaft Ahp is connected to the speed of the electric machine Mw, i.e. the speed w of the rotor 12, by a predetermined speed ratio RV which depends on the different reduction ratios of the transmission line 2. Such a predetermined speed ratio RV is known to the person skilled in the art.

[074] With reference to Figure 4, the correction module 4 comprises a conversion unit 40 configured to convert the high-pressure speed Nhp of the propulsion shaft Ahp into an electric machine speed Mw, referred to as the "time measurement Mw". Such a conversion unit 40 is simple to implement because the predetermined speed ratio RV is known. This allows to return to the reference frame of the electric machine 1 in order to achieve an optimum compensation of the torsion mode Mt.

[075] The low-pass filter 41 is applied to the time measurement Mw to provide a frequency cut-off at the level of the upper limit Fte2 of the monitoring range Ps. This removes high-frequency noise that is not related to the torsion mode Mt.

[076] The high-pass filter 42 is applied to the time measurement Mw to provide a frequency cut-off at the level of the lower limit Fte1 of the monitoring range Ps. The advantage of this is that the average component of the time measurement is removed, leaving only the wave component of the time measurement.

[077] The gain operator 43 is used to determine the desired correction level. It is preferably determined as a function of the torsion stiffness of the damping system representing the transmission line 2. The gain Kp is used to calibrate the correction so that it is effective while avoiding the risk of instability.

[078] Advantageously, the saturator 44 allows to limit the value of the correction torque TRQcorr so as not to make the correction unstable while allowing a reactive correction. It is important that the correction torque TRQcorr remains low compared with the setpoint torque TRQcons, for example, less than 10% of the setpoint torque TRQcons in transient regime of the turbomachine T and less than 1% of the setpoint torque TRQcons in steady regime.

[079] The invention has been presented for a high-pressure speed measurement Nhp because the electric machine 1 is connected to the high-pressure shaft Ahp in this example. It goes without saying that the invention applies in a similar way to a low-pressure speed measurement Nbp when the electric machine 1 is connected to the low-pressure shaft Abp.

[080] An example of implementation of a method for correcting a torsion mode of the transmission line 2 will now be presented.

[081] The method comprises the steps consisting in: - Calculating a correction torque TRQcorr from the rotational speed Nhp of the propulsion shaft Ahp over a frequency range encompassing the estimated torsion frequency Fte, referred to as the "monitoring range Ps". - Calculating a control torque TRQ* from the setpoint torque TRQcons and from the correction torque TRQcorr.

[082] Figure 6 shows a measurement of the mechanical torque received by the gearbox 24 during a time correction (curve 6a) and a frequency correction (curve 6b). Compared to Figure 5, the variations of the mechanical torque are significantly reduced. The real torsion frequency Ftr has been compensated and is no longer visible in the frequency spectrum of the curve 6b.

[083] Figure 7 shows a measurement signal S1 for the variations in mechanical torque over time for a setpoint torque TRQcons of the order of -10 N.M (generator mode) in the absence of correction (phase A) and in the presence of correction (phase B). It is worth noting that the variations are greatly attenuated in the presence of correction (phase B). The correction is also reactive, with oscillations disappearing within three periods. The effectiveness of the correction can also be seen in Figure 8, which illustrates a measurement signal S2 of the variations in mechanical torque over time for another setpoint torque TRQcons of the order of -20 N.m (generator mode) in the absence of correction (phase A) and in the presence of correction (phase B). The correction is therefore robust over a wide range of setpoint torques TRQcons.

[084] Thanks to the invention, a torsion mode in a transmission line of a hybrid turbomachine can be corrected effectively by dynamic correction of the control of the electric machine, which increases the service life of the mechanical chain and avoids the risk of breakage due to over-torque.

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