Method for detecting a torque control defect of an electric motor of a power-steering system of a motor vehicle

1. A method for detecting a fault in the control of the torque of a three-phase electric motor ( 10 ) of a power-assisted steering system of an automobile vehicle where the motor ( 10 ) has a first control connector ( 11 ), a second control connector ( 12 ), a third control connector ( 13 ), a stator ( 10 A), and a rotor ( 10 B), said method comprising steps of:

generating (E 1 ; E 2 ) a first PWM voltage signal (U′ 1 ) for controlling a first phase of the motor ( 10 ), a second PWM voltage signal (U′ 2 ) for controlling a second phase of the motor ( 10 ), and a third PWM voltage signal (U′ 3 ) for controlling a third phase of the motor ( 10 );

estimating (E 3 B 1 ; E 3 B 2 ; E 3 B 3 ; E 3 B 4 ) a direct sinusoidal current (Id_est) and a quadrature sinusoidal current (Iq_est) in a two-phase reference frame linked to the rotor ( 10 B) of the motor ( 10 ), the estimated direct sinusoidal current (Id_est) and the estimated quadrature sinusoidal current (Iq_est) being calculated from all of said first PWM voltage signal (U′ 1 ), said second PWM voltage signal (U′ 2 ), and said third PWM voltage signal (U′ 3 );

measuring (E 3 C 1 ) the first current (I′ 1 ) delivered to the first control connector ( 11 ) of the motor ( 10 ), and measuring the second current (I′ 2 ) delivered to the second control connector ( 12 ) of the motor ( 10 );

determining (E 3 C 2 ) a value of the third current (I′ 3 ), either by measuring the third current (I′ 3 ) delivered to the third control connector ( 13 ), or by estimating (E 3 C 2 ) the third current (I′ 3 ) based on the first current (I′ 1 ) and the second current (I′ 2 );

transforming (E 3 C 3 ) the first measured current (I′ 1 ), the second measured current (I′ 2 ), and the third measured or estimated current ( 13 ′) into a measured direct current (Id) and into a measured quadrature current (Iq);

determining (E 4 A; E 4 B; E 5 ) a residual direct sinusoidal voltage (Ud_res) and a residual quadrature sinusoidal voltage (Uq_res) based on all of the measured direct sinusoidal current (Id), the estimated direct sinusoidal current (Id_est), the measured quadrature sinusoidal current (Iq), and the estimated quadrature sinusoidal current (Iq_est); and

detecting (E 6 ; E 7 A; E 7 B; E 8 ) a fault when either a difference (EpsUd_res) between a value of the residual sinusoidal voltage (Ud_res) and a moving average of the residual sinusoidal voltage (Ud_res_mean) is greater than a first threshold, or a difference (EpsUq_res) between a value of the residual quadrature sinusoidal voltage (Uq_res) and a moving average of the residual quadrature sinusoidal voltage (Uq_res_mean) is greater than a second threshold.

2. The method as claimed in claim 1 , further comprising:

measuring an angle (θ mot ) of the motor and a speed of rotation (ω mot ) of the motor,

wherein a position of the rotor ( 10 B) is characterized by the angle (θ mot ), and the speed of rotation (ω mot ) is characterized by a reference frame linked to said stator ( 10 A).

3. The method as claimed in claim 2 , wherein the step of estimating the direct sinusoidal current (Id_est) and the quadrature sinusoidal current (Iq_est) comprises:

filtering said first PWM voltage signal (U′ 1 ), said second PWM voltage signal (U′ 2 ), and said third PWM voltage signal (U′ 3 ) in such a manner as to respectively obtain a first sinusoidal voltage (U 1 ), a second sinusoidal voltage (U 2 ), and a third sinusoidal voltage (U 3 ) expressed in a three-phase reference frame linked to the stator ( 10 A) of the motor ( 10 );

transforming (E 3 B 3 ) the second sinusoidal voltage (U 2 ) and the third sinusoidal voltage (U 3 ), based on the angle (θ mot ) of the rotor ( 10 B), into a direct sinusoidal voltage (Ud) and a quadrature sinusoidal voltage (Uq) expressed in a two-phase reference frame linked to the rotor ( 10 B) of the motor ( 10 ); and

determining both the estimated direct sinusoidal current (Id_est) corresponding to the direct sinusoidal voltage (Ud) and the estimated quadrature sinusoidal current (Iq_est) corresponding to the quadrature sinusoidal voltage (Uq), based on the direct sinusoidal voltage (Ud), on the quadrature sinusoidal voltage (Uq), the speed of rotation (ω mot ) of the rotor ( 10 B) of the motor ( 10 ), the residual direct sinusoidal voltage (Ud_res), and the residual quadrature sinusoidal voltage (Uq_res).

4. The method as claimed in claim 3 , wherein the step of transforming (E 3 B 3 ) the second sinusoidal voltage (U 2 ) and the third sinusoidal voltage (U 3 ) into a direct sinusoidal voltage (Ud) and a quadrature sinusoidal voltage (Uq) expressed in a two-phase reference frame linked to the rotor ( 10 B) of the motor ( 10 ) is carried out by application of a Clark transform, application of a Park transform, or application of a dqo transform.

5. The method as claimed in claim 4 , wherein the step of transforming (E 3 C 3 ) the first current (I′ 1 ) and the second current (I′ 2 ) into a direct current (Id) and into a quadrature current (Iq) is carried out based on an angular position (θ mot ) of the rotor ( 10 B) of the motor ( 10 ).

6. The method as claimed in claim 4 , wherein the step of determining the residual direct sinusoidal voltage (Ud_res) and the residual quadrature sinusoidal voltage (Uq_res) comprises:

calculating (E 4 A) a difference (EpsId) between an intensity of the direct sinusoidal current (Id) and an intensity of the estimated direct sinusoidal current (Id_est), and

calculating (E 4 B) a difference (EpsIq) between an intensity of the quadrature sinusoidal current (Iq) and an intensity of the estimated quadrature sinusoidal current (Iq_est).

7. The method as claimed in claim 4 , wherein the step of detecting the fault comprises:

calculating (E 6 ) the moving average of the residual direct sinusoidal voltage (Ud_res_mean) and the moving average of the residual quadrature sinusoidal voltage (Ud_res_mean) based on values of the residual direct sinusoidal voltage (Ud_res) and of the residual quadrature sinusoidal voltage (Uq_res) that are received continually, and using the speed (ω mot ) of rotation of the rotor ( 10 B) of the electric motor ( 10 );

calculating (E 7 A) the difference (EpsUd_res) between the value of the residual direct sinusoidal voltage (Ud_res) and the moving average of the residual direct sinusoidal voltage (Ud_res_mean); and

calculating (E 7 B) the difference (EpsUq_res) between the value of the direct sinusoidal voltage in quadrature (Uq_res) and the moving average of the direct sinusoidal voltage in quadrature (Uq_res_mean).

8. The method as claimed in claim 3 , wherein the step of transforming step (E 3 C 3 ) the first current (I′ 1 ) and the second current (I′ 2 ) into a direct current (Id) and into a quadrature current (Iq) is carried out based on an angular position (θ mot ) of the rotor ( 10 B) of the motor ( 10 ).

9. The method as claimed in claim 3 , wherein the step of determining the residual direct sinusoidal voltage (Ud_res) and the residual quadrature sinusoidal voltage (Uq_res) comprises:

calculating (E 4 A) a difference (EpsId) between an intensity of the direct sinusoidal current (Id) and an intensity of the estimated direct sinusoidal current (Id_est), and

calculating (E 4 B) a difference (EpsIq) between an intensity of the quadrature sinusoidal current (Iq) and an intensity of the estimated quadrature sinusoidal current (Iq_est).

10. The method as claimed in claim 3 , wherein the steps of detecting the fault comprises:

calculating (E 6 ) the moving average of the residual direct sinusoidal voltage (Ud_res_mean) and the moving average of the residual quadrature sinusoidal voltage (Ud_res_mean) based on values of the residual direct sinusoidal voltage (Ud_res) and of the residual quadrature sinusoidal voltage (Uq_res) that are received continually, and using the speed (ω mot ) of rotation of the rotor ( 10 B) of the electric motor ( 10 );

calculating (E 7 A) the difference (EpsUd_res) between the value of the residual direct sinusoidal voltage (Ud_res) and the moving average of the residual direct sinusoidal voltage (Ud_res_mean); and

calculating (E 7 B) the difference (EpsUq_res) between the value of the direct sinusoidal voltage in quadrature (Uq_res) and the moving average of the direct sinusoidal voltage in quadrature (Uq_res_mean).

11. The method as claimed in claim 2 , wherein the step of transforming (E 3 C 3 ) the first current (I′ 1 ) and the second current (I′ 2 ) into a direct current (Id) and into a quadrature current (Iq) is carried out based on an angular position (θ mot ) of the rotor ( 10 B) of the motor ( 10 ).

12. The method as claimed in claim 2 , wherein the step of determining the residual direct sinusoidal voltage (Ud_res) and the residual quadrature sinusoidal voltage (Uq_res) comprises:

calculating (E 4 A) a difference (EpsId) between an intensity of the direct sinusoidal current (Id) and an intensity of the estimated direct sinusoidal current (Id_est), and

calculating (E 4 B) a difference (EpsIq) between an intensity of the quadrature sinusoidal current (Iq) and an intensity of the estimated quadrature sinusoidal current (Iq_est).

13. The method as claimed in claim 2 , wherein the step of detecting the fault comprises:

calculating (E 6 ) the moving average of the residual direct sinusoidal voltage (Ud_res_mean) and the moving average of the residual quadrature sinusoidal voltage (Ud_res_mean) based on values of the residual direct sinusoidal voltage (Ud_res) and of the residual quadrature sinusoidal voltage (Uq_res) that are received continually, and using the speed (ω mot ) of rotation of the rotor ( 10 B) of the electric motor ( 10 );

calculating (E 7 A) the difference (EpsUd_res) between the value of the residual direct sinusoidal voltage (Ud_res) and the moving average of the residual direct sinusoidal voltage (Ud_res_mean); and

calculating (E 7 B) the difference (EpsUq_res) between the value of the direct sinusoidal voltage in quadrature (Uq_res) and the moving average of the direct sinusoidal voltage in quadrature (Uq_res_mean).

14. The method as claimed in claim 1 , wherein the step of transforming (E 3 C 3 ) the first current (I′ 1 ) and the second current (I′ 2 ) into a direct current (Id) and into a quadrature current (Iq) is carried out based on an angular position (θ mot ) of the rotor ( 10 B) of the motor ( 10 ).

15. The method as claimed in claim 14 , wherein the step of determining the residual direct sinusoidal voltage (Ud_res) and the residual quadrature sinusoidal voltage (Uq_res) comprises:

calculating (E 4 A) a difference (EpsId) between an intensity of the direct sinusoidal current (Id) and an intensity of the estimated direct sinusoidal current (Id_est), and

calculating (E 4 B) a difference (EpsIq) between an intensity of the quadrature sinusoidal current (Iq) and an intensity of the estimated quadrature sinusoidal current (Iq_est).

16. The method as claimed in claim 1 , wherein the step of determining the residual direct sinusoidal voltage (Ud_res) and the residual quadrature sinusoidal voltage (Uq_res) comprises:

calculating (E 4 A) a difference (EpsId) between an intensity of the direct sinusoidal current (Id) and an intensity of the estimated direct sinusoidal current (Id_est), and

calculating (E 4 B) a difference (EpsIq) between an intensity of the quadrature sinusoidal current (Iq) and an intensity of the estimated quadrature sinusoidal current (Iq_est).

17. The method as claimed in claim 1 , wherein the step of detecting the fault comprises:

calculating (E 6 ) the moving average of the residual direct sinusoidal voltage (Ud_res_mean) and the moving average of the residual quadrature sinusoidal voltage (Ud_res_mean) based on values of the residual direct sinusoidal voltage (Ud_res) and of the residual quadrature sinusoidal voltage (Uq_res) that are received continually, and using the speed (ω mot ) of rotation of the rotor ( 10 B) of the electric motor ( 10 );

calculating (E 7 A) the difference (EpsUd_res) between the value of the residual direct sinusoidal voltage (Ud_res) and the moving average of the residual direct sinusoidal voltage (Ud_res_mean); and

calculating (E 7 B) the difference (EpsUq_res) between the value of the direct sinusoidal voltage in quadrature (Uq_res) and the moving average of the direct sinusoidal voltage in quadrature (Uq_res_mean).

18. The method as claimed in claim 1 , further comprising:

correcting a reduction in a gain of the low-pass filtering means ( 150 ) based on a speed of rotation (ω mot ) of the rotor ( 10 B) of the motor ( 10 ).

19. A device for detecting a fault in control of a torque of a three-phase electric motor ( 10 ) of a power-assisted steering system of an automobile vehicle, where the motor ( 10 ) has a first control connector ( 11 ), a second control connector ( 12 ), a third control connector ( 13 ), a stator ( 10 A), and a rotor ( 10 B), said device comprising:

means ( 110 , 120 ) for generating (E 1 ; E 2 ) a first PWM voltage signal (U′ 1 ) for controlling a first phase of the motor ( 10 ), a second PWM voltage signal (U′ 2 ) for controlling a second phase of the motor ( 10 ), and a third PWM voltage signal (U′ 3 ) for controlling a third phase of the motor ( 10 );

estimating means for estimating ( 150 , 152 , 154 , 156 ) a direct sinusoidal current (Id_est) and a quadrature sinusoidal current (Iq_est) in a two-phase reference frame linked to the rotor ( 10 B) of the motor ( 10 ), the estimated direct sinusoidal current and the estimated quadrature sinusoidal current (Iq_est) being calculated from all of said first PWM voltage signal (U′ 1 ), said second PWM voltage signal (U′ 2 ), and said third PWM voltage signal (U′ 3 );

a measuring unit ( 140 ) that measures the first current (I′ 1 ) delivered to the first control connector ( 11 ) of the motor ( 10 ), that measures the second current (I′ 2 ) delivered to the second control connector ( 12 ) of the motor ( 10 ), and determines the third current (I′ 3 ) delivered to the third control connector ( 13 ) of the motor ( 10 );

a transformation unit ( 142 ) for transforming both the first current (I′ 1 ) and the second current (I′ 2 ) into a direct current (Id) and into a quadrature current (Iq);

a determination unit ( 160 ) for determining both a residual direct sinusoidal voltage (Ud_res) and a residual quadrature sinusoidal voltage (Uq_res), based on the measured direct sinusoidal current (Id), the estimated direct sinusoidal current (Id_est), the measured quadrature sinusoidal current (Iq), and the estimated quadrature sinusoidal current (Iq_est); and

a detection unit ( 190 ) that detects a fault either i) when a difference (EpsUd_res) between a value of the residual direct sinusoidal voltage (Ud_res) and a moving average of the residual direct sinusoidal voltage (Ud_res_mean) is greater than a first threshold, or ii) when a difference (EpsUq_res) between a value of the quadrature sinusoidal voltage (Uq_res) and a moving average of the quadrature sinusoidal voltage (Uq_res_mean) is greater than a second threshold.

20. An automobile vehicle comprising a three-phase electric motor ( 10 ) and a device as claimed in claim 19 , said three-phase electric motor ( 10 ) comprising a first control connector ( 11 ), a second control connector ( 12 ), a third control connector ( 13 ), a stator ( 10 A) and a rotor ( 10 B).