METHOD FOR CALIBRINGING A MODEL FOR ESTIMATING A TORQUE SUPPLIED BY AN ELECTRIC MACHINE

Description

TECHNICAL FIELD

[0001] This application relates to a method for calibrating a model for estimating the torque supplied by an electrical machine. The application also relates to a calibration device for estimating the torque supplied by an electrical machine. TECHNOLOGICAL BACKGROUND

[0002] A machine, whether thermal or electrical, can be a motor or a generator, and is typically used in industry to supply power to a system. In particular, electric machines are currently used to provide propulsive power to aircraft propulsion systems such as helicopter rotors, propellers, or turbojet engines. The machine delivers mechanical power in the form of torque and speed to a rotating shaft. The machine is controlled by an electronic control system to maintain a set speed or torque that meets the system's requirements.

[0003] Controlling the torque supplied by the machine during operation is crucial for the proper functioning of the system. In particular, when an electric machine is used for aircraft propulsion, torque control is a critical flight safety issue. Indeed, applying an incorrect torque can have critical consequences for flight safety. Applying excessive torque can lead to exceeding the maximum torque for which the mechanical transmission chain was designed, thus generating damage that can lead to the failure of a critical component such as a helicopter's main gearbox or a propeller. Applying insufficient torque, that is, torque lower than the maximum torque the propulsion system should be able to provide, can result in a lack of propulsive power, which can be critical during certain phases of flight.

[0004] Uncertainty in the torque information provided by the machine is taken into account in the design of the machine and its control system to ensure flight safety. However, significant uncertainty leads either to oversizing the mechanical transmission and thus increasing the aircraft's empty weight, or to reducing the aircraft's performance (payload, range, etc.), which diminishes its economic viability.

[0005] Torque information from a thermal or electrical machine can be obtained by direct measurement using a torque sensor, also called a torque meter, located, for example, on the motor shaft of the thermal machine or elsewhere in the mechanical transmission chain. Such a sensor generally measures the deformation of a mechanical part subjected to the torque supplied by the machine. The measurement obtained is precise. However, it requires dedicated electronics, with the associated issues of fault management and reliability; a sensor calibration procedure is generally necessary to obtain the desired accuracy; finally, a torque sensor is a heavy, bulky, and expensive device, which therefore has a negative impact on the system design. In the case of electrical machines, the electronic control system is based on measuring the electric current flowing through the machine using a current sensor.It is then possible to estimate the torque supplied by the electric machine using the following relationship: T = Kt * I, where T is the torque, I is the electric current in the machine, and Kt is a torque constant characteristic of the machine in question. This estimation method, based on indirect torque measurement, is simple and inexpensive in terms of integration (cost, mass, reliability) since it relies on a current sensor included in the design. However, such a torque estimate lacks precision. For an electric machine intended for use in an aeronautical propulsion system, this lack of precision in the estimated torque value poses a problem for flight safety.

[0006] The main factors contributing to inaccuracy in the indirect measurement of torque supplied by an electrical machine via an electric current measurement are: the measurement of the electric current itself, which generally has an accuracy of the order of + / -5 to 10% of the full measurement scale, the torque constant Kt of the electric machine, which is a characteristic associated with a given machine topology, but which can vary according to manufacturing and assembly tolerances, the order of magnitude of the dispersion on the value Kt also being + / - 5 to 10% of the "average" nominal value, and various other sources of inaccuracy, including those related to the control electronics of the electric machine, the operational conditions of use and in particular temperature, the electrical supply voltage, or even aging, etc.

[0007] In the prior art, CN 106 452 266 B discloses a method for calibrating an electric motor by automatically determining the torque estimation model for the motor, this model establishing a relationship between the input current and the corresponding output torque. CN 111 812 506 A also discloses a method for calibrating an electric motor by automatically determining the torque estimation model for the motor, in which the model calibration points are obtained iteratively.US document 2003 / 218439 A1 discloses a diagnostic method for an electric motor comprising a current regulator and a control unit, the latter including a table containing the relationship between the torque setpoint and the current required to obtain the torque corresponding to the setpoint, and a model containing the relationship between the torque setpoint and the estimated voltage at the output of the current regulator. GENERAL STATEMENT

[0008] One aim of this application is to propose a calibration method for a torque estimation model supplied by an electrical machine and a corresponding calibration device, allowing to improve the accuracy of a torque estimation based on an electric current measurement in the electrical machine, which makes it possible to do away with the need to integrate a specific torque measurement sensor with integration problems (cost, mass, weight) and reliability, and which is simple to implement.

[0009] According to one aspect, the present application relates to a calibration method for a model estimating the torque supplied by an electrical machine, in particular by a permanent magnet motor, comprising the following steps: E1 measurement of an electric current in the electric machine for an operating point of the electric machine; E2 estimation of the torque supplied by the electric machine for said operating point of the electric machine, from the measured electric current and the estimation model associating an output torque with an input electric current; E3 measurement of a reference torque supplied by the electric machine for said operating point of the electric machine; E4 comparison of the estimated torque with the reference torque; and E5 based on said comparison, adjustment of the estimation model so as to reduce, or even cancel, a difference between the estimated torque and the reference torque.

[0010] Some preferred but not limiting characteristics of the calibration process according to the first aspect are the following, taken individually or in combination: the method further includes a step E6 of recording the adjusted estimation model in a memory of a control system; steps E1 to E4 are repeated for several different operating points of the electrical machine; the estimation model includes an affine function, and wherein the adjustment of the estimation model includes an adjustment of a slope and / or an ordinate of the affine function; the estimation model includes a lookup table associating each of a plurality of electrical input currents with a corresponding output torque, and wherein the estimation of the torque in step E2 includes a recalibration of at least one output torque value from the lookup table in step E5 as a function of the comparison between the estimated torque and the reference torque carried out in step E4, so as to reduce or even cancel the difference between the estimated torque and the reference torque;the estimation model includes a set of lookup tables, each lookup table being associated with a temperature from among a set of operating temperatures of the electric machine, and in which the estimation of the torque in step E2 includes a substep of selecting a lookup table associated with a temperature of the electric machine at the operating point; the estimation model is adjusted so as to reduce, or even cancel, a difference between the estimated torque and the reference torque, over a predetermined range of electric current [Ik, In], and / or for a predetermined range of operating temperature;and / or the process includes: a calibration step of the electric machine, including a substep of measuring the no-load electromotive force of the electric machine and a substep of measuring a rotational speed of the electric machine, for an operating point of the electric machine, and a substep of determining an electric machine model associating with the electromotive force a rotational speed of the electric machine, from the measured electromotive force and rotational speed;a calibration step of the control system, comprising a substep of measuring an electric current in the control system on a static load bank equipped with a standard current sensor to obtain a reference current measurement, a substep of calculating a measurement error of the squared current of the control system with respect to the reference current measurement, and a substep of creating a conformation model in order to correct the current measurement controlled by the control system from the reference current measurement; and a step of recording in the control unit the electrical machine model and the conformation model of the control system.

[0011] According to a second aspect, the present application proposes a calibration device for estimating the torque supplied by an electrical machine, in particular by a permanent magnet motor, comprising: an electric current measuring device adapted to measure the electric current in the electric machine for an operating point of the electric machine; an estimation model associating an output torque with an input electric current, such that the estimation model is adapted to estimate a torque supplied by the electric machine for said operating point of the electric machine, from the measured electric current; a torque meter adapted to measure a reference torque supplied by the electric machine for said operating point of the electric machine; and a control unit adapted to compare the estimated torque with the reference torque, the control unit being further adapted to adjust the estimation model based on said comparison, so as to reduce, or even eliminate, a difference between the estimated torque and the reference torque.

[0012] Optionally, the calibration device according to the second aspect also includes: a first chamber adapted to reproduce first external conditions, the first chamber being adapted to receive the electrical machine during calibration; and a second chamber adapted to reproduce second external conditions, the second chamber being adapted to receive the control system of the electrical machine during calibration. DESCRIPTION OF THE FIGURES

[0013] Other features, objectives and advantages of this application will become apparent upon reading the detailed description that follows, given by way of non-limiting example, which will be illustrated by the following figures: There figure 1 is a diagram illustrating a calibration device for estimating the torque supplied by an electrical machine according to one embodiment. figures 2a And 2bThese are graphs illustrating the calibration of a torque estimation model supplied by an electrical machine, obtained through a calibration process according to a specific embodiment. figure 3 is a diagram illustrating a calibration method for estimating the torque supplied by an electrical machine according to one embodiment. figure 4 is a diagram illustrating a step in estimating the torque supplied by an electrical machine within a calibration process according to one embodiment. figure 5 is a diagram illustrating a calibration step of an electrical machine, a calibration step of a control system, and a recording step of an estimation model in a control unit, within the framework of a calibration process according to an embodiment. DETAILED DESCRIPTION

[0014] A calibration method, also called a conformation method, for a model estimating the torque supplied by an electrical machine 10, in particular by a permanent magnet motor, is illustrated by way of non-limiting example in figure 3 The calibration process includes the following steps: E1: measurement of an electric current in the electric machine 10 for an operating point of the electric machine 10; E2: estimation of the torque supplied by the electric machine 10 for said operating point of the electric machine 10, from the measured electric current and an estimation model associating an output torque with an input electric current; E3: measurement of a reference torque supplied by the electric machine 10 for said operating point of the electric machine 10; E4: comparison of the estimated torque with the reference torque; and E5: based on said comparison, adjustment of the estimation model so as to reduce, or even cancel, a difference between the estimated torque and the reference torque.

[0015] The estimation model may, for example, be intended for use in flight during the operation of an electric machine 10 intended to provide torque to an aircraft propulsion system.

[0016] The torque estimation is thus carried out by indirect measurement, from the measurement of electric current in the electric machine 10. Consequently, we benefit from a precise torque estimation, which avoids the need for a specific torque measurement sensor, and which uses a sensor 30 for measuring the electric current in the electric machine 10 which is naturally present.

[0017] The calibration of the torque estimation model is thus performed on a complete chain including, in particular, an electric current measurement device 30, a control system 20 for the electric machine 10, and the electric machine 10 itself, and not on a partial chain that would only include the electric machine 10. Furthermore, the calibration is performed for a specific operating point that is representative of the operating conditions of the electric machine 10 during its use. Thus, once calibrated, the estimation model allows for an accurate estimation of the torque delivered by the electric machine 10 during its subsequent operation, based on a measurement of the electric current at the machine's input.

[0018] The calibration process for the torque estimation model reduces, or even eliminates, the inaccuracies associated with indirect torque measurement via electrical current measurement. This includes the uncertainty related to the electrical current measurement itself and the manufacturing tolerances of the electric machine 10. The torque delivered by the electric machine 10 is therefore estimated with reduced uncertainty, making it suitable for use in aeronautical propulsion. Indeed, calibrating the torque estimation model meets flight safety requirements due to the improved accuracy of the torque measurement. This allows for a precise correlation between the electrical current at the machine's input and the torque delivered at the machine's output. The torque delivered by the electric machine 10 can thus be better controlled.This mastery allows for more precise control of the electric machine 10, so that the torque supplied by the electric machine 10 during the different phases of flight is maximized, while ensuring that the maximum torque for which the mechanical transmission chain was designed is not exceeded and thus not risk damaging it. Calibration device

[0019] A calibration device for estimating the torque supplied by an electrical machine 10, in particular by a permanent magnet motor, is illustrated by way of non-limiting example in figure 1 The calibration device includes: an electric current measuring device 30 adapted to measure the electric current in the electric machine 10 for an operating point of the electric machine 10; advantageously, an electric current measuring device 30 already present in the electric machine 10 (and therefore usable in other processes relating to the electric machine 10) can be used, which makes it possible not to increase the size or mass of the electric machine 10; an estimation model associating an output torque with an input electric current, so that the estimation model is adapted to estimate a torque supplied by the electric machine 10 for said operating point of the electric machine 10, from the electric current measured by the measuring device 30;a calibration unit 50 comprising a torque meter 40 adapted to measure a reference torque supplied by the electric machine 10 for the operating point of the electric machine 10; and adapted to compare the estimated torque with the reference torque, the control unit 50 being further adapted to adjust the estimation model according to said comparison, so as to reduce, or even eliminate, a difference between the estimated torque and the reference torque; and a test bench 60 adapted to receive the electric machine 10 for the calibration of the torque estimation model.

[0020] The torque meter 40 can in particular be integrated into the test bench 60. In all cases, it is not necessary to integrate the torque meter into the electric machine 10 itself, the torque meter 40 integrated into the test bench 60 on the ground is sufficient to calibrate the torque estimation model provided by the electric machine 10.

[0021] The electrical current measurement device 30 corresponds to the current sensor intended for the application. In practice, this can be a Hall effect sensor, a shunt, a magnetoresistive sensor, or a fluxgate sensor. The type of electrical current measurement device 30 is chosen based on various criteria, such as: the desired measurement accuracy, the available space for integration, and the cost of the electrical current measurement device 30. For example, we have seen that a Hall effect sensor has a smaller footprint and lower cost, but lower accuracy, than a fluxgate sensor. The objective of this application is to enable the use of a current measurement sensor with lower accuracy and cost, such as a Hall effect sensor, by providing a method and device for calibrating the torque estimation model from this current measurement.

[0022] In practice, the electric current measuring device 30 can be located at the level of the electric machine 10, or at the level of the control system 20. The measured electric current corresponds to the electric current flowing in one phase of the electric machine 10, at the point of operation.

[0023] The calibration device is suitable for implementing the process described above, and therefore offers the same advantages of calibration accuracy without increasing the cost, mass or size of the system as the process described above.

[0024] The control system 20 of the electric machine 10 is adapted to control the rotational speed and supply voltage of the electric machine 10. The control system 20 of the electric machine 10 practically comprises control electronics and power electronics of the electric machine 10.

[0025] Power electronics include means for controlling the electric current flowing in the electrical machine 10, which are adapted to the type of electrical machine 10, such as a power converter, for example an inverter or a rectifier. Control electronics enable the control of the power electronics.

[0026] The method described above allows calibration to be performed on the entire system, including the complete electronic / electrical power chain, from the control system 20 to the electric motor 10 – including the power harness where applicable. Consequently, uncertainties are reduced across the entire system, and not just those affecting the electric motor 10 or the control system 20 of the electric motor 10 alone.

[0027] The process may further include a step E6 of recording the adjusted estimation model in a memory of the control system 20.

[0028] Steps E1 to E4 can be repeated for several different operating points of the electric machine 10. Each operating point can be defined by one or more parameters of the electric machine, including, in particular, a temperature, a rotational speed, and a supply voltage of the electric machine. In other words, each operating point is defined by a given value or a combination (n-tuple) of values ​​of operating parameters of the electric machine.

[0029] In more detail, for each operating point of the electric machine 10, the calibration process comprises the following steps: an electrical current at the input of the electric machine 10 on the test bench 60 is measured in step E1, a torque supplied by the electric machine 10 is estimated in step E2, a reference torque is measured by the torque meter on the test bench 60 in step E3, and the estimated torque is compared with the reference torque in step E4. In particular, different operating points of the electric machine 10 can correspond to different electrical currents in the electric machine 10. Therefore, repeating steps E1 to E4 for different operating points allows for the estimation of different torques, each corresponding to the different measured electrical currents. Thus, the calibration is more precise and takes into account different operating conditions of the electric machine 10.The more operating points there are, the more accurate the calibration of the torque estimation model and the improved robustness of the torque estimation model.

[0030] The calibration process for the torque estimation model provided by the electric machine 10 can be carried out after the electric machine 10 has been received and before it is integrated into the propulsion system (aircraft) to which it is to supply power. In other words, the calibration of the estimation model is performed on the ground, using the calibration unit 50 (on the test bench 60). This calibration of the torque estimation model is what allows, in flight, for an accurate estimation of the torque provided by the electric machine 10 based on the estimator's input parameters: current in particular, and possibly supply voltage and / or temperature as will be explained, guaranteeing optimal torque for each phase of flight, in terms of propulsive efficiency and flight safety.

[0031] In the case where in the application (aircraft) concerned, a power harness 70, i.e. a set of electrical cables capable of carrying power signals between the remote control system 20 and the electric machine 10 itself, it is provided that the calibration device and method incorporate such a power harness 70 in order to take into account the whole set formed by the complete electronic / electrical power chain (from the control system 20 to the electric motor 10). Torque estimation (step E2)

[0032] The estimation of the torque supplied by the machine is carried out in step E2 from the electric current measured in step E1 and an estimation model associating an output torque with an input electric current by the calibration unit 50.

[0033] An overall electric current range [I1, In] includes all the electric currents that can be applied to the input of the electric machine 10 in operation, i.e. during the different flight phases of the aircraft; it is therefore the set of electric currents measured during step E1.

[0034] The calibration of the estimation model is preferably performed over the entire overall electrical current range [I1, In] to obtain the best accuracy across the entire operating range of the machine (all flight phases). The adjustment of the estimation model performed in step E5 over the overall electrical current range [I1, In] minimizes the difference between the set of estimated torques and the set of reference torques.

[0035] In one variant, the calibration of the estimation model can be performed on a predetermined electrical current range [Ik, In], which is a reduced range within the overall electrical current range [I1, In]. This allows for particularly precise calibration within this reduced range, as it is specifically optimized for this smaller range. Such a predetermined electrical current range [Ik, In], reduced relative to the overall electrical current range [I1, ..., In], will typically include a selection of the electrical currents measured during step E1.The adjustment of the estimation model performed in step E5 then applies to the predetermined electric current range [Ik, In]. In other words, this step E5 takes into account the torques estimated from the measured electric currents that fall within this range, and does not take into account the torques estimated from measured electric currents located outside the predetermined electric current range [Ik, In]. This results in a particularly precise calibration within the predetermined electric current range [Ik, In], but less precise calibration outside this range [Ik, In].

[0036] The predetermined electrical current range [Ik, In] may correspond to a preferred operating range of the electrical machine 10, or to a critical operating current range of the electrical machine 10, within which calibration must be particularly precise. For example, in the field of aeronautical propulsion, the need for precision is particularly acute near the maximum torque, and therefore near the maximum electrical current that can be applied to the electrical machine 10 during operation. Indeed, the power transmission sizing and the maximum power correspond to a torque range located close to the maximum torque.Thus, the predetermined electric current range [Ik, In] can correspond to an electric current range between 90 and 100% of the maximum current value for the electric machine 10 considered, which corresponds to a torque range between 80 and 100% of the maximum torque value defined for the propulsion chain considered.

[0037] The calibration process and device presented therefore make it possible to calibrate a defined estimation model for a given electric motor and propulsion chain. Calibration of the estimation model

[0038] Several usage models can be used. Estimation model based on an affine function

[0039] The estimation model to be calibrated can, in a first example, be an affine function, that is, a law that is a linear function of the measured electric current, and which relates the output torque to the input electric current. Such an affine function is defined by two parameters: a y-intercept and a slope.

[0040] The method and device for calibrating such an affine function allow the parameters of the affine function to be adjusted.

[0041] To this end, initial values ​​of these parameters, y-intercept and slope, define an initial affine function recorded in a memory of the calibration unit 50 during step E6, and the calibration process makes it possible to obtain a final affine function, from the reference torque measurements for different input current measurements corresponding to different operating points of the machine.

[0042] We denote Tini, the initial affine function Tini of the estimation model to be calibrated. The initial affine function Tini is defined by an initial ordinate at the origin Bini and an initial slope Ktini, and provides a torque value Tini(x) from an input current measured I0 by application of the equation EQ1: Tini (x)= Ktini * lini + Bi.

[0043] The adjustment of the estimation model performed in step E5 includes an adjustment of the initial slope Ktini and / or the initial y-intercept Bini of the initial linear function Tini. More specifically, the values ​​of the parameters of the slope and / or y-intercept of the initial linear function Tini can be recalibrated by comparing the measured reference estimated torques for different machine operating points, such that the total distance of the estimated torques to the corresponding measured reference torques T1, ..., Tn is minimized or even eliminated. A final linear function Tfin is obtained by calibrating the estimation model, defined by the new parameters Ktfin and / or Bfin, such that a more accurate estimated torque value, denoted T*, is obtained for the electric current measurement Ii (for i an integer from 1 (or k in the case of a reduced range) to n, and n being the number of operating points used).This value T* is given by: T* = Ktfin * Ii + Bfin.

[0044] The final affine function Tfin can in practice be obtained by performing a linear regression on the set of reference pairs measured in step E3, or on a selection of reference pairs from this set, corresponding to a range of interest as explained above.

[0045] There figure 2aThis illustrates, by way of non-limiting example, an estimation model that is fitted in step E5 to minimize the distance between the torques estimated in step E2 and the reference torques T1, ..., Tn measured in step E3, over the overall electric current range [I1, In]. Starting from the set of different torques estimated by the initial affine function Tini, the final affine function Tfin is obtained by performing a linear regression on the set of corresponding measured reference torques T1, ..., Tn. The y-intercept and / or slope of the torque estimation affine function are thus fitted so that the final affine function Tfin corresponds to the linear regression on the set of measured reference torques T1, ..., Tn over the considered overall electric current range [I1, In].

[0046] There figure 2bThis illustrates, by way of non-limiting example, an estimation model that is fitted in step E5 to minimize the distance between a selection of torques estimated in step E2 over the predetermined electric current range [Ik, In] corresponding to a range of interest, and a corresponding selection of reference torques Tk, ..., Tn measured in step E3 over the predetermined electric current range [Ik, In]. The final affine function Tfin is obtained by performing a linear regression on the selection of measured reference torques Tk, ..., Tn for the predetermined electric current range [Ik, In]. The initial y-intercept Bi and / or the initial slope Ktini of the torque estimation affine function are thus fitted so that the final affine function Tfin corresponds to the linear regression on the selection of measured reference torques Tk, ...Tn for electric currents located within the predetermined electric current range [Ik, In] considered. Thus, the calibration of the torque estimation model is particularly accurate over the predetermined electric current range [Ik, In] of interest. Estimation model based on a polynomial function

[0047] In another example, the estimation model is based on a polynomial function of degree strictly greater than 1, for example, a quadratic or cubic function. The estimation model is adapted to estimate the output torque as a function of the input electric current and coefficients associated with each degree of the polynomial function. The estimation model therefore includes parameters corresponding to the coefficients associated with each degree of the polynomial function. These parameters are then stored in the memory of the control system 20 of the electric machine 10 during step E6.

[0048] Such a polynomial function of degree strictly greater than 1 allows us to account for non-linearities in estimating torque from electric current, for example, when the torque constant of the electric machine depends on the electric current. Indeed, a weakening of the torque constant is generally observed when the electric machine reaches the "magnetic saturation elbow," close to the maximum current. The fitting of the parameters of the polynomial function of degree strictly greater than 1 at step E5 can be carried out over the overall electric current range [I1, In], or over a more restricted, predetermined electric current range [Ik, In], which is of particular interest in a manner similar to that described above for the affine function. Estimation model based on any other function relating the measured electric current to the estimated torque

[0049] More generally, the estimation model includes any function that allows estimating the torque supplied by the electric machine 10 from a measurement of the electric current in the electric machine 10. The estimation model includes the parameter(s) that define the function relating the measured electric current to the estimated torque. These parameters can be stored in the memory of the control system 20 during step E6 and adjusted in a manner similar to that presented and described above. Estimation model based on a lookup table

[0050] In yet another example, the estimation model includes a lookup table that associates each of a plurality of input electrical currents with a corresponding estimated output torque. The estimation model's lookup table thus comprises a plurality of input electrical currents and a plurality of corresponding estimated output torques. The adjustment of the estimation model performed in step E5 then involves adjusting one or more input electrical currents and / or their associated output torques from the lookup table. In other words, one or more output torque values ​​from the lookup table are recalibrated in step E5 based on the comparison between the estimated torque and the reference torque performed in step E4, so as to reduce or even eliminate any difference between the estimated and reference torques.Thus, when the current measurements taken during the calibration test exactly match the initial input current values, only the torque values ​​are updated; conversely, if they do not match, both the input current and associated torque values ​​are updated so that the table matches the values ​​recorded during the calibration test. Using a lookup table therefore means that it is not necessary to compare the torque estimated by the initial table with the torque actually measured. Entering the measured torque values ​​into the table minimizes the error between the estimated torque obtained with the final table and the actual (measured) torque. The error is therefore necessarily zero for operating points that exactly match the table's input values ​​(currents).Between these points, the error depends on the interpolation function used, the distance between the points and the non-linearity of the real pair over the interval between the points in the table.

[0051] Using a lookup table allows for precise calibration of the torque estimate provided by the electric machine 10, particularly when the relationship between the estimated torque and the measured electrical current is not easily approximated by a mathematical function. The calibration accuracy then also depends on the number of points in the lookup table (corresponding to a pair of measured current and torque values). The more measured input electrical current values ​​the lookup table contains, associated with the estimated output torques for a given electrical current range, the more accurate the calibration.

[0052] Optionally, as illustrated by way of non-limiting example in figure 4 , the estimation of the torque in step E2 may include a substep E21 of comparing the electric current measured in step E1 with one or more electric currents from among the plurality of input electric currents, and a substep E22 of interpolation to deduce the estimated torque supplied by the electric machine 10.

[0053] For example, the interpolation in substep E22 can be a linear interpolation. In particular, if the electric current measured in step E1 lies between the first and second adjacent input electric currents in the lookup table, then the torque delivered by the electric machine 10 can be estimated by linear interpolation between the first output torque and the second adjacent output torque, associated respectively with the first and second input electric currents. Thus, the relative distance between the measured electric current and the first input electric current, and between the measured electric current and the second input electric current, is equal to the relative distance between the estimated torque and the first output torque, and between the estimated torque and the second output torque, respectively. Taking other variables into account

[0054] The lookup table can be a one-dimensional lookup table, said dimension corresponding to the electric current measured in the electric machine 10. Such a one-dimensional lookup table makes it possible to compensate for the sensitivity of the magnetic flux to the electric current, to increase the accuracy of the estimation of the torque supplied by the electric machine 10. Indeed, a saturation elbow phenomenon of the field induces a smaller variation of the torque for high electric currents than for lower electric currents.

[0055] Alternatively, the lookup table can be a multidimensional lookup table. The lookup table can include a first dimension corresponding to the electric current measured in the electrical machine 10, and one or more additional dimensions corresponding to: at a temperature, which may correspond to a temperature to which the electrical machine 10 is subjected and / or to a temperature to which the control system 20 is subjected; and / or to a supply voltage and a rotational speed of the electrical machine 10.

[0056] The plurality of input electrical currents associated with the plurality of output torques is then determined for each temperature and / or supply voltage and rotational speed in the lookup table. In other words, the estimation model comprises one or more sets of lookup tables, with a first set of lookup tables associated with a temperature and / or a second set of lookup tables associated with a supply voltage and a rotational speed. The torque estimation in step E2 then includes a substep E23 of selecting a lookup table associated with a temperature and / or supply voltage and rotational speed of the electrical machine 10 at the operating point of the electrical machine for which the electrical current is measured in step E1.

[0057] Such a multi-dimensional lookup table makes it possible to compensate for the sensitivity of the determination of the torque supplied by the electric machine 10 to various surrounding factors, such as the variability of the torque constant of the electric machine with temperature (the influence of temperature on the magnetic field produced by the magnets and on the reluctance of the stator laminations) or the variability of the measurement error of the current sensors with temperature, which makes it possible to further improve the accuracy of the calibration.

[0058] The temperature to which the electrical machine 10 and / or the control system 20 is subjected may, for example, correspond to a temperature measured as close as possible to the electronic components of the electrical machine 10 and / or the control system, or in the external environment close to the electrical machine 10 and / or the control system.

[0059] A lookup table including an additional dimension corresponding to the temperature to which the electric machine 10 and / or the control system 20 is subjected thus makes it possible to compensate for the sensitivity of the measurement of the electric current in the electric machine 10 to the temperature and / or the influence of the temperature on the torque supplied by the electric machine 10 for a given electric current, and therefore to further increase the accuracy of the calibration of the torque estimation model.

[0060] For example, the lookup table can be a two-dimensional table, the second dimension corresponding to the temperature to which the electrical machine 10 and / or the control system 20 are subjected. In other words, the estimation model includes a set of lookup tables, each lookup table being associated with a temperature from among a set of operating temperatures of the electrical machine 10. The torque estimation in step E2 includes a step E23 of selecting a lookup table associated with a temperature of the electrical machine 10 at the operating point.

[0061] The selection step E23 may include applying a time-domain filter representing a dynamic model of temperature evolution. The time-domain filter is configured to model the temperature difference between a temperature measurement point (typically the stator windings of the electric machine 10) and a point of interest for that temperature parameter (typically the magnets on the rotor of the electric machine 10). The selected lookup table best matches the temperature at the point of interest, as it influences the torque constant Kt of the electric motor, thus further improving the calibration accuracy of the torque estimation model. The time-domain filter therefore models the inertia in the temperature variation between the measurement point and the point of interest.The time filter can be calibrated by measurements on test bench 60, using specific instrumentation to accurately measure the temperature at the temperature measurement point which will be available (measurable) in operation (during flight phases) and at the point of interest.

[0062] A lookup table with an additional dimension corresponding to a supply voltage and a rotational speed of the electric machine 10 is particularly useful in the case of a permanent magnet motor, which may be subjected to significant variations in supply voltage and / or rotational speed during operation. In such cases, a control system known as flux deflection control is generally used to adapt the operation of the electric machine 10 to different supply voltages and rotational speeds. The torque delivered by the electric machine 10 then depends on the combination of the supply voltage and the rotational speed of the electric machine 10.The lookup table can, for example, be a single lookup table whose additional dimension corresponds to the ratio between the supply voltage and the rotational speed, or alternatively be a lookup table comprising a first additional dimension corresponding to the supply voltage and a second additional dimension corresponding to the rotational speed.

[0063] The lookup table(s) of the estimation model can be stored in the memory of the control system 20 of the electric machine during step E6.

[0064] The lookup table(s) of the estimation model are fitted in step E5 to minimize the distance between the torques estimated in step E2 and the reference torques T1, ..., Tn measured in step E3, over the overall electric current range [I1, In], or over the predetermined electric current range [Ik, ..., In]. In other words, the modification in step E5 of the output torques and, where applicable, the associated input electric currents can be carried out over the overall electric current range [I1, In], or over the predetermined electric current range [Ik, In], in a manner similar to that described above for the estimation model including an affine function.

[0065] It will be understood that taking into account the operating parameters of the electrical machine, and in particular the temperature to which the electrical machine 10 and / or the control system 20 are subjected, and / or the supply voltage and the rotational speed of the electrical machine 10, in addition to measuring the electrical current to provide an estimated value of the output torque of the electrical machine, applies similarly to cases where the relationship between current and torque can be modeled by a mathematical function, in particular affine or polynomial, or other, provided that corresponding measurements are available. Thus, everything that has been said with regard to measuring and taking into account the temperature, or measuring and taking into account the supply voltage and rotational speed with regard to flux deflux, applies similarly to these estimation functions.

[0066] More specifically, the estimation model then includes a function—for example, an affine function, a polynomial function of degree strictly greater than 1, or any other conceivable type—comprising one or more independent variables that associate a measured input electrical current with an estimate of a corresponding output torque for different values ​​or ranges of values ​​of these additional parameters. For example, a first variable could be associated with a temperature and / or a supply voltage and a rotational speed.The torque estimation in step E2 then includes a substep E23 for determining an independent variable associated with a temperature and / or an independent variable associated with a supply voltage and rotational speed of the electric machine 10 at the operating point of the electric machine 10 for which the electric current is measured in step E1, and / or a variable associated with the ratio between the supply voltage and the rotational speed. The estimation model thus compensates for the sensitivity of the electric current measurement in the electric machine 10 to the temperature and / or the supply voltage and rotational speed, and / or compensates for the influence of the temperature and / or the supply voltage and rotational speed on the torque delivered by the electric machine 10 for a given electric current, thereby further increasing the accuracy of the torque estimation model calibration. Calibration process sequence First embodiment - simultaneous calibration of the electronic control system 10 and the electrical machine 10

[0067] The process includes a preliminary step of installing the electrical machine 10 on a test bench 60.

[0068] The process includes a step E0 of checking the calibration device, in particular checking the electrical machine 10 by the control system 20, so as to reach the operating point.

[0069] Each operating point of the electric machine 10 can be defined in practice by a rotational speed of the electric machine 10 and / or by a power level supplied by the electric machine 10 and / or by a temperature to which the electric machine 10 is subjected and / or by a temperature to which the control system 20 of the electric machine 10 is subjected and / or by an electric current in the electric machine 10. Indeed, the estimation of torque from the measurement of electric current, as well as the means of measuring electric current, can be sensitive to operating conditions, particularly temperature. Thus, an operating point that depends, in particular, on temperature allows for a more precise calibration of the torque estimation.

[0070] To enable the calibration of estimation functions or the establishment of correspondence tables and to take into account the influence of temperature, the calibration device includes at least a first thermal chamber in which at least the electric motor 10 is placed, allowing the reference torque measurements to be taken at the output of the electric motor at different operating points and for different temperatures.

[0071] The calibration device preferably includes at least two, or even three, thermal chambers, allowing for the best possible reproduction of the operational temperature conditions for the different types of installation / design of the electrical machine 10 and its control electronics, which may be close together and at roughly the same temperature, or on the contrary remote and connected by a power harness.

[0072] It is then possible to place each of the functional blocks among the electric motor 10, the control system 20 and the power harness 70, under temperature conditions representative of actual operational use: a first chamber 110 adapted to reproduce first external conditions, the first chamber 110 being adapted to receive the electrical machine 10 during calibration; a second chamber 120 adapted to reproduce second external conditions, the second chamber 120 being adapted to receive the control system 20 of the electrical machine 10 during calibration; and optionally, a third chamber 130 adapted to reproduce third external conditions, the third chamber 130 being adapted to receive the power harness 70 when the control system 20 is located away from the electrical machine 10, the power harness 70 connecting the electrical machine 10 to the control system 20. The temperature of the cables of the power harness 70 - which influences their electrical resistance - also influences the measured electrical current.By providing a thermal enclosure 130 specific to the power harness 70, we can therefore better take into account the influence, in the measurement of the electric current, of the temperature on the resistance of the cables of the power harness 70.

[0073] The first external conditions may include a first temperature T°1. The second external conditions may include a second temperature T°2, which may be equal to or different from the first temperature T°1. Thus, the conditions reproduced in the first chamber 110 may be identical to or different from those reproduced in the second chamber 120. These two chambers 110 and 120 therefore allow us to model either the case where the electrical machine 10 and the control system 20 are subjected to the same external conditions, or the case where the electrical machine 10 and the control system 20 are subjected to different external conditions.

[0074] The first external conditions reproduced by the first chamber 110 can correspond substantially to the conditions likely to be encountered by the electrical machine 10 during its operation. The second external conditions reproduced by the second chamber 120 can correspond substantially to the conditions likely to be encountered by the control system 20 of the electrical machine 10 during its operation. Thus, the electrical machine 10 and its control system 20 can each be subjected to identical or different external conditions, representative of their respective operating conditions. The third external conditions may include a third temperature T°3, which may be equal to or different from the first temperature T°1 and / or the second temperature T°2.

[0075] When the electric machine 10 and the control system 20 are likely to be subjected to substantially identical external conditions during their operation, the electric machine 10 and the control system 20 may both be placed in the first enclosure 110, or they may be placed respectively in the first enclosure 110 and the second enclosure 120, the first and second external conditions then being identical. Optionally, when the power harness 70 is also likely to be subjected to substantially identical external conditions to those of the electric machine 10 and the control system 20, the power harness 70 may be placed in the first enclosure 110, respectively in the second enclosure 120, or it may be located in the third enclosure 130, the first, second, and third external conditions then being identical.

[0076] When the control system 20 is embedded in the electrical machine 10, these two functional blocks are close together and can be considered to be subject to homogeneous temperature conditions.

[0077] They could therefore be placed in the same enclosure 110, or in two separate enclosures 110 and 120, but configured to reproduce essentially identical external conditions, particularly temperature conditions, over the range of variation of these conditions. The temperatures to which the electrical machine 10 and the control system 20 are likely to be subjected can vary over large amplitudes, for example, depending on: of the ambient atmospheric temperature, which in the aeronautical field can vary from -50°C to +70°C, of ​​the temperature in the immediate environment of the electric machine 10, which can be affected by the operation of other equipment, for example the temperature in an engine compartment such as an aircraft nacelle or a helicopter engine compartment depends strongly on the operation of the gas turbine, of the temperature of the electrical elements and electronic components of the electric machine 10 and of the control system 20, which varies strongly with the operating power of the electric machine 10 itself due to self-heating caused by the flow of electric current.

[0078] When the control system 20 of the electric machine 10 is located remotely from the electric machine 10, a power harness 70 connects these two functional units. The electric machine 10, the control system 20, and the power harness 70 are then generally subjected to significantly different temperature conditions.

[0079] In particular, the electric machine 10 and its electromagnetic components can be subjected to extreme temperatures, for example above 100°C, especially when the electric machine 10 is located in an engine compartment such as an aircraft nacelle or a helicopter engine compartment. Conversely, the control system 20 can be subjected to lower temperatures when it is relocated to a more protected environment where the temperature is maintained in a lower, or even very low, range, for example below 20°C or below -40°C.An operating point of the electric machine 10 can for example be reached for a given rotational speed and / or supply voltage of the electric machine 10 placed in the first enclosure 110 reproducing a temperature above 100°C, the control system 20 being placed in the second enclosure 120 reproducing a temperature below -40°C, a harness 70 being, where appropriate, placed in one of the first and second enclosures 110, 120 or in a third dedicated enclosure 130, according to the conditions likely to be encountered by the harness 70.

[0080] Such a calibration procedure, using one or more chambers 110, 120, 130 comprising the electric machine 10 and / or the control system 20 and / or the power harness 70, allows for a comprehensive calibration of the entire system, including the electric machine 10, the control system 20 of the electric machine 10, and, where applicable, the power harness 70. This procedure minimizes uncertainties related to all environmental and topological parameters of the system, resulting in a more reliable, precise, and easier calibration. By characterizing the control system 20 and the electric machine 10 as a whole, the calibration procedure is also simple to perform while ensuring the production of an accurate and robust torque estimation model under operating conditions. Second embodiment – ​​separate calibration of the electronic control system 20 and the electrical machine 10

[0081] In a second example of implementation, as illustrated by way of non-limiting example in figure 5The electronic control system 20 and the electric machine 10 are calibrated separately. This simplifies the implementation of the invention during maintenance, particularly when the control system 20 is remote and must be replaced in case of failure. Specifically, it is proposed here to calibrate the control system 20 and the electric machine 10 independently of each other. More precisely, in this embodiment, the current measurement of the control system 20 is characterized using a standard current measurement system to obtain a conformation table of the current measurement as a function of the current actually controlled by the power electronics of the control system 20 and, where applicable, the operating conditions that may affect the accuracy of the current measurement of the control system (e.g., ambient temperature, supply voltage, etc.) (step E200).This conformation table is therefore specific to each control system 20. An electric motor 10 can thus be associated with any control system 20 by simply loading the conformation table obtained for that control system 20. Similarly, the torque constant of the electric machine 10 is characterized as a function of the applied current, measured using the standard current measurement system, and compared to the torque value measured using test equipment (torque meter on the test bench) (step E100). This yields a torque conformation table as a function of the current flowing through the motor and, where applicable, the operating conditions. This torque conformation table is therefore specific to each electric motor 10. A control system can thus be associated with any electric motor 10 by simply loading the torque conformation table obtained for that electric motor 10.

[0082] Thus, by using a reference system for determining the estimation model, it is then possible to obtain a model, valid for a given electric motor 10, but adaptable by simple matching to any electronic control system, without requiring recalibration of the electronic control system when it needs to be changed.

[0083] To this end, the calibration process includes: a calibration step E100 of the electric machine 10, comprising a substep E101 of measuring the no-load electromotive force of the electric machine 10 and a substep E102 of measuring a rotational speed of the electric machine 10, for an operating point of the electric machine 10, and a substep E103 of determining an electric machine model associating the electromotive force with a rotational speed of the electric machine 10, from the measured electromotive force and rotational speed; a calibration step E200 of the control system 20, comprising a substep E201 of measuring an electric current of the power electronics of the control system 20 on a static load bank equipped with a standard current sensor serving as a reference (and where applicable, a harness 70);a substep E202 for calculating the measurement error of the root mean square current of the control system 20 relative to the reference standard current sensor. These measurements can be performed for different current setpoints to cover a current range of interest, optionally for different operating conditions that may affect the accuracy of the control system current measurement (e.g., ambient temperature, supply voltage, etc.). Advantageously, measuring the reference current on a static load bank provides robust and highly accurate measurements;and a substep E203 of creating a conformation model associating the reference current measurement with the current actually controlled by the power electronics, and optionally with operating conditions (temperature, rotational speed, etc.), in order to determine correction parameters for the electric current controlled by the power electronics of the control system 20 from the current measured by the standard current sensor serving as a reference; and a step E300 of recording in the control unit 50 the electric machine model and the conformation model in a memory of the control system 20.

[0084] The calibration of the electric machine 10 at step E100, or of the control system 20 at step E200, therefore remains valid even when the control system 20, or the electric machine 10, is changed, for example, in the event of a failure of the control system 20, or the electric machine 10. In particular, if the control system 20 is located remotely from the electric machine 10, the control system 20 may need to be changed frequently during system maintenance, independently of the electric machine 10. The control system can thus be associated with any electric machine by loading the conformation table of the torque estimator associated with the controlled machine.

[0085] The estimation model is defined by independently considering the electrical machine model and the control system model. The estimation model can be the sum of the electrical machine model and the control system model. The control unit 50 can thus be associated with any electrical machine 10 and / or any control system 20, provided that the electrical machine model or the control system model is changed if the electrical machine 10 or the control system 20 is replaced.

[0086] The measurement of the no-load electromotive force is carried out in sub-step E101 by operating the electric machine 10 under no-load conditions, i.e. without load, in order to collect the no-load electromotive force data, where appropriate as a function of the temperature of the electric machine 10. Several electromotive force measurements at different operating temperatures of the electric machine 10 can be carried out, in order to obtain a table of electromotive forces as a function of temperature.

[0087] The electromotive force (EMF) is the voltage generated by the electric machine 10 when it is rotated at a certain speed. The relationship between the rotational speed of the electric machine 10 and the electromotive force is identical to the relationship between electric current and torque.

[0088] The calibration of the electric machine 10 is therefore carried out in step E100 by identifying the relationship between the rotational speed of the electric machine 10 and the electromotive force. This allows for the precise deduction of the relationship between the measured electric current and the torque supplied by the electric machine 10, as these relationships are identical. In other words, from the estimation of the relationship between current and torque, via the measurement of the electromotive force, and the measurement of the reference current by the standard current sensor used as a reference on the static load bank, it is possible to construct the torque estimation model (table or function). The electric machine model determined in substep E103 includes one or more parameters associating the measured electric current with a torque supplied by the electric machine 10, possibly also taking into account other operating parameters, such as temperature, quadrature current, etc.

[0089] Substep E201 of the electric current measurement in the electric machine 10 can include three electric current measurements: Ia, Ib, and Ic, which are the currents flowing in each phase of the electric machine 10. The reference electric current Iq can be calculated, in a manner known per se, from these three electric current measurements: Iq = function (Ia, Ib, Ic), this function being a 3x3 matrix that depends on the position measurement of the electric machine's rotor (Park transformation). Thus, the electric current measurement is reconstructed by calculation from the phase current measurements of the electric machine 10.

[0090] The control system model associates the measured electric current with the calculated quadrature current and the electric current controlled by the control system 20: Imes = function (Iq, Iref).

[0091] The control system model created in substep E203 can further associate a temperature of the control system 20 with the measured electric current: Imes = function (Iq, Iref, T°2).

[0092] When the control system 20 (or possibly the electric machine 10) is replaced, the old control system model is replaced by the new control system model (respectively, of the electric machine), which is obtained by calibrating the new control system 20 at stage E200 (respectively, of the new electric machine at stage E100).

[0093] The calibration parameters of the electric machine model can be stored in a memory of the control system 20 intended for the electric machine 10. Thus, it is simple to program the control system 20 which must be paired with the electric machine 10, with the calibration parameters of the current measurement.

[0094] Optionally, and for the calibration parameters of the electric machine 10 itself, in particular the torque coefficient Kt, it is advantageous to physically attach a memory card to the electric machine 10, with an ad hoc interface between this card and the control system 20, to record these parameters.

[0095] Other embodiments may be considered and a person skilled in the art may easily modify the embodiments or examples set out above or consider others while remaining within the scope of the claims of this application.

Claims

1. A calibrating method for a model for estimating a torque provided by an electric machine (10), particularly by a permanent-magnet motor, comprising the following steps: E1: measuring an electric current through the electric machine (10) for an operating point of the electric machine (10); E2: estimating the torque provided by the electric machine (10) for said operating point of the electric machine (10), based on the electric current measured and on the estimation model associating an output torque with an input electric current; E3: measuring a reference torque provided by the electric machine (10) for said operating point of the electric machine (10); E4: comparing the estimated torque with the reference torque; and E5: as a function of said comparison, adjusting the estimation model so as to reduce, or even cancel out, a difference between the estimated torque and the reference torque.

2. The calibrating method as claimed in claim 1, further comprising a step E6 of storing the adjusted estimation model in a memory of a control system (20).

3. The calibrating method as claimed in any of claims 1 and 2, wherein the steps E1 to E4 are repeated for several different operating points of the electric machine (10).

4. The calibrating method as claimed in any of claims 1 to 3, wherein the estimation model comprises an affine function, and wherein the adjustment of the estimation model comprises an adjustment of a gradient and / or of a y-intercept of the affine function.

5. The calibrating method as claimed in any of claims 1 to 3, wherein the estimation model comprises a lookup table associating with each of a plurality of electric input currents a corresponding output torque, and wherein the estimating of the torque in the step E2 comprises a recalibration of at least one output torque value of the lookup table during the step E5 as a function of the comparison between the estimated torque and the reference torque made in the step E4, such as to reduce or even cancel out the difference between the estimated torque and the reference torque.

6. The calibrating method as claimed in claim 5, wherein the estimation model comprises a set of lookup tables, each lookup table being associated with a temperature from among a set of operating temperatures of the electric machine (10), and wherein the estimating of the torque in the step E2 comprises a sub-step (E23) of selecting a lookup table associated with a temperature of the electric machine (10) at the operating point.

7. The calibrating method as claimed in any of claims 1 to 6, wherein the estimation model is adjusted so as to reduce, or even cancel out, a difference between the estimated torque and the reference torque, over a predetermined electric current range [Ik, In], and / or for a predetermined operating temperature range.

8. The calibrating method as claimed in any of claims 1 to 7, comprising: - a step (E100) of calibrating the electric machine (10), comprising a sub-step (E101) of measuring the no-load electromotive force of the electric machine (10) and a sub-step (E102) of measuring a rotation speed of the electric machine (10), for an operating point of the electric machine (10), and a sub-step (E103) of determining an electric machine model associating with the electromotive force a rotation speed of the electric machine (10), based on the measured electromotive force and the measured rotation speed; - a step (E200) of calibrating the control system (20), comprising a sub-step (E201) of measuring an electric current through the control system (20) on a static load test bench equipped with a master current sensor to obtain a reference current measurement, a sub-step (E202) of computing a measurement error on the quadratic current of the control system (20) with respect to the measurement of the reference current, and a sub-step (E203) of creating a shaping model in order to correct the current measurement commanded by the control system (20) based on the reference current measurement; and - a step (E300) of storing the electric machine model and the shaping model of the control system in the control unit (50).

9. A calibrating device for estimating a torque provided by an electric machine (10), particularly by a permanent-magnet motor, comprising: - a device for measuring an electric current suitable for measuring the electric current through the electric machine (10) for an operating point of the electric machine (10); - an estimation model associating an output torque with an input electric current, such that the estimation model is suitable for estimating a torque provided by the electric machine (10) for said operating point of the electric machine (10), based on the measured electric current; - a torquemeter (40) suitable for measuring a reference torque provided by the electric machine (10) for said operating point of the electric machine (10); and - a control unit (50) suitable for comparing the estimated torque with the reference torque, the control unit (50) being moreover suitable for adjusting the estimation model as a function of said comparison, so as to reduce, or even cancel out, a difference between the estimated torque and the reference torque.

10. The calibrating device as claimed in claim 9, further comprising: - a first chamber (110) suitable for replicating first external conditions, the first chamber (110) being suitable for receiving the electric machine (10) during the calibration; and - a second chamber (120) suitable for replicating second external conditions, the second chamber (120) being suitable for receiving the control system (20) of the electric machine (10) during the calibration.