METHOD FOR DETERMINING AN ESTIMATED CURRENT OF A THREE-PHASE ELECTRIC MOTOR IN DEGRADED MODE

Abstract

A method for determining an estimated current flowing through a winding of a motor that is then controlled on two active phases. A measured voltage is measured for each of the two active phases at the input of the winding, the two measured voltages are corrected to produce a respective corrected voltage, a temperature-compensated resistance of the motor is determined, and at least one estimated current flowing through each of the two active phases, respectively, of the winding is determined on the basis of the temperature-compensated resistance of the motor and the measured voltages of the two active phases.

Claims

1. A method for determining an estimated current (Iestx, Iesty) flowing through a winding of a permanent-magnet synchronous three-phase electric motor (M) of the type comprising at least one winding controllable by a switching device, the method comprising, the motor (M) then being controlled on two active phases, a third phase being in an open state: measuring a measured voltage (Ux, Uy) for each of the two active phases at the input of the winding, correcting the two measured voltages (Ux, Uy) to produce a respective corrected voltage (Umesx, Umesy), determining a temperature-compensated resistance (Rmot) of the motor, and determining at least one estimated current (Iestx, Iesty) flowing through each of the two active phases, respectively, of the winding on the basis of the temperature-compensated resistance (Rmot) of the motor and the measured voltages (Umesx, Umesy) of the two active phases by solving the following equations, x being the first active phase and y being the second active phase of the two active phases: $\left[\mathrm{Iestx}\right]=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Lmot}\right]\left[\frac{\mathrm{dImesx}}{\mathrm{dt}}\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Rmot}\right]}\left[\mathrm{Iesty}\right]=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesy}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Lmot}\right]\left[\frac{\mathrm{dImesy}}{\mathrm{dt}}\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Rmot}\right]}$ in which equations Lmot is an inductance of the motor (M) at 20 C. and 0 ampere, is a flux of the motor (M) at 20 C. and 0 ampere, .sub.mot is a speed of rotation of the motor (M), .sub.mot is an angular position of a rotor of the motor (M), k being a constant equal to 0 for phase 1, to 1 for phase 2 and to 2 for phase 3.

2. The method as claimed in claim 1, wherein the estimated currents (Iestx, Iesty) are determined by using a numerical analysis method for approximation of differential equations.

3. The method as claimed in claim 2, wherein the selected numerical analysis method for approximation of differential equations is the second-order Runge-Kutta method, with the following equations for calculating the estimated current (Iestx) for phase x, which is one of the two active phases: ${\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_n=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Rmot}\right]\left[{\mathrm{Iestx}}_n\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Lmot}\right]}\left[{\mathrm{Iestx}}_{n+\frac{1}{2}}\right]=\left[{\mathrm{Iestx}}_n\right]+{{\frac{t}{2}\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_n\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_{n+\frac{1}{2}}=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Rmot}\right]\left[{\mathrm{Iestx}}_{n+\frac{1}{2}}\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Lmot}\right]}\left[{\mathrm{Iestx}}_{n+1}\right]=\left[{\mathrm{Iestx}}_n\right]+{t\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_{n+\frac{1}{2}}$ in which t is the sampling time for the calculation and n is the number of iterations, the equations for calculating the estimated current (Iesty) for phase y, which is the other one of the two active phases, being similar, with x being swapped for y and vice versa in the above equations.

4. The method as claimed in claim 1, wherein the correction of the two measured voltages (Ux, Uy) to produce a respective corrected voltage (Umesx, Umesy) is carried out initially by filtering of the measured voltages (Ux, Uy), which are then in the form of square waves, by means of a low-pass filter to produce a respective sinusoidal voltage, and then by compensation of the respective sinusoidal voltages by means of a compensator capable of compensating for the attenuating effects of the low-pass filter to produce a respective corrected voltage (Umesx, Umesy).

5. The method as claimed in claim 4, wherein the low-pass filter is a second- or higher-order low-pass filter.

6. The estimation method as claimed in claim 4, wherein the compensation uses an interpolation table on the basis of a speed of rotation (.sub.mot) of the motor (M).

7. The method as claimed in claim 1, wherein the determination of the resistance (Rmot) of the motor is temperature-compensated by taking a mean temperature (Tmos) of the electronic elements of the switching device that are located near a temperature sensor, the resistance (Rmot) being compensated according to the following equation:
Rmot=Rmot20*(1+0.004*(Tmos20 C.)) 0.004 being the temperature coefficient of copper, and Rmot20 corresponding to the resistance of one phase of the motor (M) at 20 C.

8. A method for diagnosing a validity of measurements of a measured current (Imesx, Imesy) flowing through a respective phase of a winding of a permanent-magnet synchronous three-phase electric motor (M) of the type comprising at least one winding controllable by a switching device, the motor (M) then being controlled on two active phases, a third phase being in an open state, comprising: the measured current (Imesx, Imesy) flowing through at least one of the two active phases is measured, an estimated current (Iestx, Iesty) flowing through at least one of the two active phases of the winding is determined by means of the estimation method as claimed in claim 1, a respective sliding standard deviation (Iecx or Iecy), for at least one of the two active phases, of a difference between the measured current (Imesx, Imesy) and the estimated current (Iestx, Iesty) for said at least one of the two active phases over a sliding horizon of a number of samples is calculated according to one of the following formulae, respectively: $\mathrm{Iecx}=\sqrt{\frac{\underset{i=1}{\overset{i=\mathrm{NbSample}}{.Math.}}{\left(\mathrm{Imesx}-\mathrm{Iestx}\right)}^2}{\mathrm{NbSample}}}$ $\mathrm{Iecy}=\sqrt{\frac{\underset{i=1}{\overset{i=\mathrm{NbSample}}{.Math.}}{\left(\mathrm{Imesy}-\mathrm{Iesty}\right)}^2}{\mathrm{NbSample}}}$ NbSample being the number of samples, the respective sliding standard deviation (Iecx, Iecy) for said at least one of the two active phases is compared with a predetermined threshold value, wherein, when the standard deviation is higher than the predetermined threshold value, an error in the measured currents (Imesx, Imesy) is diagnosed for said at least one phase and, when the standard deviation is lower than the predetermined threshold value, a validity of the measured currents (Imesx, Imesy) is diagnosed for said at least one of the two active phases.

9. The diagnosis method as claimed in claim 8, wherein it is implemented on the two active phases, with or without measurement of the current in the second active phase and, when the current is not measured in the second active phase, the value of the current in this second active phase is extrapolated from the measured current (Imesx or Imesy) of the first active phase, being equal to the negative value of the current of the first phase, the standard deviation being calculated according to the above formula given for this second phase.

10. The diagnosis method as claimed in claim 8, wherein the samples are taken in a range of angular positions of the motor (M) corresponding to a stabilized current in said at least one of the two phases.

11. The diagnosis method as claimed in claim 8, wherein it is applied to a physical or virtual current sensor capable of measuring a current in said at least one of the two active phases, the current sensor being characterized as faulty when the standard deviation is higher than the predetermined threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Other features, aims and advantages of aspects of the present invention will become apparent on reading the detailed description that follows and on examining the appended drawings provided by way of non-limiting examples, in which:

[0046] FIG. 1 illustrates a method according to an aspect of the present invention for diagnosing a validity of measurements of a measured current flowing through a respective phase of a winding of a permanent-magnet synchronous three-phase electric motor of the type comprising at least one winding controllable by a switching device, the motor then being controlled on two active phases, which is performed by calculating a deviation between the measured current and the estimated current for the two active phases,

[0047] FIG. 2 shows a flow diagram of the diagnosis method according to one embodiment of the present invention,

[0048] FIGS. 3A and 3B show current intensity and torque curves for angles of rotation of the motor, these curves being employed to define a sampling zone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] Referring more particularly to FIG. 1, an aspect of the present invention relates to a method for determining an estimated current Iestx, Iesty flowing through a winding of a permanent-magnet synchronous three-phase electric motor M of the type comprising at least one winding controllable by a switching device 11.

[0050] In FIG. 1, it is an inverter that bears the reference 11 given to the switching device, the inverter being part of the switching device.

[0051] This determination method takes place with a motor M that is then controlled on two active phases, a third phase being in an open state.

[0052] The switching device comprises a DC-to-AC inverter 11 that is supplied with power by an external source at a DC voltage Ubat, which may be the voltage of a battery of a motor vehicle. The inverter 11 transforms a DC voltage into a square-wave voltage, for which the voltages of the two phases x and y supplying power to the motor M are Ux and Uy, respectively.

[0053] A voltage is measured for each of the two active phases at the input of the winding. The two measured voltages Ux, Uy are then corrected to produce a respective corrected voltage. This correction is carried out in two consecutive modules 1 and 2.

[0054] In the first module 1, which may advantageously be a low-pass filter, the measured voltages are square-wave voltages at the input, and at the output the obtained voltages are sinusoidal voltages.

[0055] In the second module 2, which is a compensation module 2 or a compensator, the respective sinusoidal voltages are respectively compensated by a compensator capable of compensating for the attenuating effects of the low-pass filter to produce a respective corrected measured voltage Umesx and Umesy.

[0056] In parallel with the corrected measured voltages Umesx and Umesy being obtained, a temperature-compensated phase electrical resistance of the motor M is determined. This is carried out consecutively in the modules 3 and 4 on the basis of a temperature Tsens detected by a sensor near the switching device and the electronic elements to give a temperature of the switching device Tmos. This temperature is extrapolated to give the temperature of the motor M and to proceed to correct the resistance of the motor M.

[0057] On the basis of the corrected measured voltages Umesx and Umesy and of the temperature-compensated electrical resistance Rmot of the motor M, at least one estimated current Iestx or Iesty flowing through one of the two active phases, respectively, of the winding is determined by solving the following equations, x being the first active phase and y being the second active phase of the two active phases:

[00004]$\left[\mathrm{Iestx}\right]=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Lmot}\right]\left[\frac{\mathrm{dImesx}}{\mathrm{dt}}\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Rmot}\right]}\left[\mathrm{Iesty}\right]=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesy}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Lmot}\right]\left[\frac{\mathrm{dImesy}}{\mathrm{dt}}\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Rmot}\right]}$

in which equations Lmot is an inductance of the motor M at 20 C. and 0 ampere, is a flux of the motor M at 20 C. and 0 ampere, .sub.mot is a speed of rotation of the motor M, .sub.mot is an angular position of a rotor of the motor M, k being a constant equal to 0 for phase 1, to 1 for phase 2 and to 2 for phase 3.

[0058] This is carried out in an estimation module for estimating the currents flowing through each phase, which is referenced 5 in FIG. 1, with the two estimated currents Iestx and Iesty at the output of the estimation module 5.

[0059] The determination is carried out on the basis of an electrical model in degraded mode of a permanent-magnet three-phase synchronous motor M, with the assumption that the system is balanced, i.e. that there is no impedance imbalance between the active phases of the motor M.

[0060] There are a plurality of ways to solve the above equations, and two preferred ways are described below. The estimated currents Iestx, Iesty can be determined by using a numerical analysis method for approximation of differential equations.

[0061] In a first optional embodiment, which is not preferred, a Euler method can be applied in a single iteration according to the following equations:

[00005]${\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_n=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Rmot}\right]\left[{\mathrm{Iestx}}_n\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Lmot}\right]}\left[{\mathrm{Iestx}}_{n+1}\right]=\left[{\mathrm{Iestx}}_n\right]+{t\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_n$

[0062] In a second, preferred optional embodiment, the selected numerical analysis method for approximation of differential equations may be the second-order Runge-Kutta method.

[0063] The following equations can then be solved to calculate the estimated current Iestx for phase x, which is one of the two active phases:

[00006]${\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_n=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Rmot}\right]\left[{\mathrm{Iestx}}_n\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Lmot}\right]}\left[{\mathrm{Iestx}}_{n+\frac{1}{2}}\right]=\left[{\mathrm{Iestx}}_n\right]+{{\frac{t}{2}\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_n\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_{n+\frac{1}{2}}=\frac{\begin{array}{c}\begin{array}{c}\left[\mathrm{Umesx}-\left(\frac{\mathrm{Umesx}+\mathrm{Umesy}}{2}\right)\right]-\\ \left[\mathrm{Rmot}\right]\left[{\mathrm{Iestx}}_{n+\frac{1}{2}}\right]+\frac{\sqrt{3}}{2}**\end{array}\\ {}_{\mathrm{mot}}*\sin \left(\mathrm{mot}+\frac{}{6}-k\frac{2}{3}\right)\end{array}}{\left[\mathrm{Lmot}\right]}\left[{\mathrm{Iestx}}_{n+1}\right]=\left[{\mathrm{Iestx}}_n\right]+{t\left[\frac{\mathrm{dIestx}}{\mathrm{dt}}\right]}_{n+\frac{1}{2}}$

in which t is the sampling time for the calculation and n is the number of iterations, the other parameters having been identified previously.

[0064] For phase y, the equations for calculating the estimated current Iesty for phase y, which is the other one of the two active phases, are similar, with x being swapped for y and y for x in the above equations.

[0065] Returning to the correction of the two measured voltages in the modules 1 and 2, this correction of the two measured voltages to produce a respective corrected voltage can be carried out initially by filtering 1 of the measured voltages, which are then in the form of square waves, by means of a low-pass filter in the module 1 to produce a respective sinusoidal voltage, and then by compensation 2 of the respective sinusoidal voltages by means of a compensator capable of compensating for the attenuating effects of the low-pass filter to produce a respective corrected voltage.

[0066] During the filtering 1, the low-pass filter may be a second- or higher-order low-pass filter for filtering the square-wave voltages applied to the motor phases M, which allows demodulation by filtering the carrier corresponding to the frequency of the pulse-width modulations of a system for pulse-width modulation of the voltage.

[0067] During the compensation 2, an interpolation table on the basis of a speed of rotation .sub.mot of the motor M can be used by way of a position speed module 10. The reduction in the gain of the amplitudes of at least one of the two voltages of the active phases due to the filters is thus corrected on the basis of the speed of rotation .sub.mot of the motor M. The position speed module 10 is the measurement of speed and position module for the rotor of the motor M.

[0068] With regard to the determination of the resistance of the motor M, the resistance of the motor M can be temperature-compensated by taking the resistance Rmot20 of the motor M at ambient temperature, which is known.

[0069] To this end, a mean temperature Tmos of the electronic elements of the switching device that are arranged near a temperature sensor that detects a temperature Tsens can be taken. The resistance Rmot of the motor M can then be compensated on the basis of the mean temperature Tmos of the electronic elements of the switching device 11 according to the following equation:

Rmot=Rmot20*(1+0.004*Tmos20 C.)

0.004 being the temperature coefficient of copper, and Rmot20 corresponding to the resistance of one phase of the motor M at 20 C.

[0070] A preferred application of the method for determining an estimated current Iestx, Iesty flowing through a winding of a motor M is intended for a method for diagnosing a validity of measurements of a measured current flowing through a respective phase of a winding of a permanent-magnet synchronous three-phase electric motor M of the type comprising at least one winding controllable by a switching device 11, the motor M then always being controlled on two active phases, a third phase being in an open state.

[0071] In this method, the measured current flowing through at least one of the two active phases, advantageously through both active phases, is measured. This is carried out by the measurement module 9 in FIG. 1, this measurement module 9 being able to measure a current of one phase or the currents Imesx, Imesy of two active phases.

[0072] An estimated current Iestx, Iesty flowing through at least one of the two active phases of the winding is also determined by means of the estimation method as described above, with the estimated current values Iestx, Iesty being obtained.

[0073] Then, a respective sliding standard deviation, for at least one of the two active phases, of a difference between the measured current and the estimated current Iestx, Iesty for said at least one of the two active phases over a sliding horizon of a number of samples is calculated according to one of the following formulae, respectively, which are for one of the two phases, respectively:

[00007]$\mathrm{Iecx}=\sqrt{\frac{\underset{i=1}{\overset{i=\mathrm{NbSample}}{.Math.}}{\left(\mathrm{Imesx}-\mathrm{Iestx}\right)}^2}{\mathrm{NbSample}}}$$\mathrm{or}$$\mathrm{Iecy}=\sqrt{\frac{\underset{i=1}{\overset{i=\mathrm{NbSample}}{.Math.}}{\left(\mathrm{Imesy}-\mathrm{Iesty}\right)}^2}{\mathrm{NbSample}}}$

[0074] NbSample being the number of samples.

[0075] Finally, the respective sliding standard deviation for said at least one of the two active phases is compared with a predetermined threshold value. When the standard deviation is higher than the predetermined threshold value, an error in the measured currents Imesx or Imesy is diagnosed for said at least one phase, while, when the standard deviation is lower than the predetermined threshold value, a validity of the measured currents Imesx or Imesy is diagnosed for said at least one of the two active phases.

[0076] The predetermined threshold value may take into account the worst-case measurement errors by taking into account the whole of the measurement chain and all the possible drifts, including thermal, sampling, power supply, calibration, and other drifts.

[0077] FIG. 1 shows a fault-detection module 6 that implements the diagnosis method described above by evaluating a standard deviation or the standard deviations lecx and lecy. One or more measured current values Imesx and Imesy, and one or more estimated current values Iestx, Iesty for at least one phase, and preferably for both active phases, are transmitted at the input of this fault-detection module 6.

[0078] The diagnosis method according to an aspect of the invention can be implemented on the two active phases. This can be carried out with or without measurement of the current in the second active phase. If the current is not measured for the second active phase, the value of the measured current in this second active phase is extrapolated from the measured current Imesx or Imesy of the first active phase, being equal to the negative value of the current of the first phase, the standard deviation being calculated according to the above formula given for this second phase.

[0079] FIG. 2 shows a flow diagram of the diagnosis method according to an aspect of the present invention, including the method for determining an estimated current Iestx, Iesty.

[0080] In a branch of the flow diagram on the left-hand side, one or more measured voltage measurements Ux, Uy are corrected in a filtering operation 1 and a compensation operation 2 to give one or more corrected voltage measurements Umesx, Umesy.

[0081] In parallel, a phase electrical resistance Rmot20 of the motor is taken at ambient external temperature during stoppage of the motor M, said resistance being compensated by calculating a temperature taken by a sensor and extrapolated to the electronic elements of the switching device near the motor M at reference 3, and then by compensating the resistance of the motor M by means of this extrapolated temperature at reference 4 to obtain a compensated electrical resistance Rmot of the motor.

[0082] The estimated intensity Iestx, Iesty, for one phase or for both phases, of the one or more currents flowing through one or each phase, is then calculated at reference 5.

[0083] One or more measured current values Imesx, Imesy, which are advantageously measured by a sensor, are supplied at 9 on the basis of the actual current intensity or intensities Ix, Iy at the input of the motor. These measured values may differ from the actual current intensity values Ix, Iy, if the measurement is faulty.

[0084] At reference 6, a fault in the measurements of the current intensities is detected by evaluating a respective sliding between standard deviation, for at least one of the two active phases, of a difference between the measured current Imesx, Imesy and the estimated current Iestx, Iesty for the active phase or both active phases.

[0085] For the diagnosis method, the number of samples NbSample is chosen to determine a horizon of a duration longer than a minimum value that is high enough to perform filtering and avoid false alerts.

[0086] Conversely, the number of samples NbSample is chosen to determine a horizon of a duration shorter than a maximum value that presents a risk in terms of continuing to control the motor M in the presence of a fault in the intensity measurement, for example in a sensor.

[0087] Without this being limiting, the horizon may be between 10 and 15 milliseconds, with a sampling period of 500 microseconds. In these cases, the number of samples may be between 20 and 30.

[0088] The samples should be taken in a range of angular positions of the motor M corresponding to a stabilized current in said at least one of the two phases.

[0089] FIGS. 3A and 3B show a current intensity I of the motor M and a motor torque C, respectively, as a function of the electrical angular position angle mot of the motor for each of the two current phases.

[0090] The shape of the current in degraded mode is shown in FIG. 3A. Preferably, the detection of an error and the diagnosis method can be implemented in a zone in which the current remains relatively stabilized with a low variation gradient. This corresponds to the zone formed by the trough in FIG. 3A.

[0091] It is therefore advantageous for sampling of the currents to be diagnosed to take place only in the pit of this trough on the basis of the angular position of the electric motor M, in a range of electrical angular positions of the motor M the angle mot is within a range corresponding to the trough.

[0092] Given a sampling window of 1 rad, and TetaRef1 being the reference, the reference window extends between TetaRef10.5 rad and TetaRef1+0.5 rad or between TetaRef10.5 rad+n and TetaRef1+0.5 rad+n; the method selects the measured current Imesx and the estimated current Iestx or Iesty with:

[0093] TetaRef1=0 rad if phase 1 is faulty

[0094] TetaRef1=2 n/3 if phase 2 is faulty

[0095] TetaRef1=4 n/3 rad if phase 3 is faulty.

[0096] This diagnosis is valid when the motor M is controlled on two phases.

[0097] Advantageously, it is applied to a physical current sensor, i.e. one that is actually present, or a virtual current sensor, in the latter case the software, which is capable of measuring a current in said at least one of the two active phases, the current sensor being characterized as faulty when the standard deviation is higher than the predetermined threshold value.

[0098] When a current sensor is characterized as faulty, the intensity measurement from said sensor can be replaced by an estimated current intensity measurement Iestx, Iesty. The motor M can then continue to be controlled with this new estimated current intensity value Iestx, Iesty.