Power train for a transport vehicle, in particular a rail vehicle, and method for controlling same

1. A power train for a transport vehicle comprising:

an electric motor including a shaft, a stator and a rotor, the rotor being rotatable around an axis of the shaft;

a power supply system receiving a direct input voltage and delivering a polyphase voltage to the motor, the power supply system having a modulation factor equal to a voltage amplitude of each phase of the motor divided by the direct input voltage;

a sensor of a signal representative of the rotational speed of the rotor; and

a control device for varying the modulation factor that decreases the modulation factor relative to the modulation factor in the absence of a means for varying the modulation factor, when a speed of rotation of the rotor belongs to a first interval of values below a predetermined transition value, and adapted to increase the modulation factor relative to the modulation factor in the absence of a means for varying the modulation factor, when the speed of rotation of the rotor belongs to a second interval of values greater than the predetermined transition value.

2. The power train according to claim 1 , wherein the rotor is adapted to create a proper magnetic rotor field in a first magnetic direction and to be passed through by another magnetic field, a magnetic rotor field being the sum of the proper magnetic rotor field and the other magnetic field, the proper magnetic rotor field creating a proper rotor flow through the rotor, and wherein the control device varies the flow of the magnetic rotor field through the rotor, adapted to decrease the flow of the magnetic rotor field relative to the proper rotor flow, when the speed of rotation of the rotor belongs to the first interval, and adapted to increase the flow of the magnetic rotor field relative to the proper rotor flow, when the speed of rotation of the rotor belongs to the second interval.

3. The power train according to claim 2 , wherein the control device includes a first generator for generating a main polyphase current intended to power the stator, to create a main magnetic stator field oriented in a second magnetic direction separate from the first magnetic direction, and a second generator for generating an additional out-of-phase current relative to the main current and intended to power the stator, to create a secondary magnetic stator field substantially oriented in the first magnetic direction, the additional current having a first sign to decrease the flow of the magnetic rotor field relative to the proper rotor flow, and a sign opposite the first sign to increase the flow of the magnetic rotor field relative to the proper rotor flow.

4. The power train according to claim 3 , further comprising a receiver for acquiring a signal representative of the motor torque, and wherein an intensity of the additional current depends on the value of the motor torque.

5. The power train according to claim 4 , wherein the absolute value of the intensity of the additional current is lower for the high values of the motor torque than for the low values of the motor torque.

6. The power train according to claim 1 , further comprising a receiver for acquiring a signal representative of the motor torque, and wherein the modulation factor depends on the value of the motor torque.

7. The power train according to claim 1 , wherein the predetermined transition value is greater than the value of the speed of rotation of the rotor corresponding to the modulation factor equal to 50%, in the absence of a means for varying the modulation factor.

8. The power train according to claim 1 , further comprising a receiver for acquiring a signal representative of the motor torque, and wherein the predetermined transition value depends on the value of the motor torque.

9. The power train according to claim 8 , wherein the predetermined transition value is lower for high values of the motor torque than for low values of the motor torque.

10. The power train according to claim 1 , wherein the union of the first interval and the second interval is connected.

11. The power train according to claim 1 , wherein the motor is a synchronous motor.

12. The power train according to claim 11 , wherein the synchronous motor is a permanent magnet synchronous motor.

13. A transport vehicle, comprising a power train according to claim 1 .

14. A method for controlling a power train for a transport vehicle comprising an electric motor comprising a shaft, a stator and a rotor, the rotor being rotatable around the axis of the shaft, the method comprising the steps of:

providing the motor with a polyphase voltage, using a power supply system receiving a direct input voltage and delivering the polyphase voltage, the system having a modulation factor equal to the voltage amplitude of each phase divided by the direct input voltage;

measuring the speed of rotation of the rotor;

decreasing the modulation factor relative to the modulation factor in the absence of a means for varying the modulation factor, when the speed of rotation of the rotor belongs to a first interval of values below a predetermined transition value; and

increasing the modulation factor relative to the modulation factor in the absence of a means for varying the modulation factor, when the speed of rotation of the rotor belongs to a second interval of values greater than the predetermined transition value.

15. The control method according to claim 14 , wherein the rotor is adapted to create a proper magnetic rotor field in a first magnetic direction and to be passed through by another magnetic field, a magnetic rotor field being the sum of the proper magnetic rotor field and the other magnetic field, the proper magnetic rotor field creating a proper rotor flow through the rotor, the method further comprising:

decreasing the flow of the magnetic rotor field through the rotor relative to the proper rotor flow, when the speed of rotation of the rotor belongs to the first interval; and

increasing the flow of the magnetic rotor field relative to the proper rotor flow, when the speed of rotation of the rotor belongs to the second interval.

16. The transport vehicle according to claim 13 wherein the transport vehicle is a rail vehicle.

17. The power train for a transport vehicle according to claim 1 wherein the transport vehicle is a rail vehicle.