METHOD AND DEVICE FOR ESTIMATING THE TORQUE RIPPLE OF AN ELECTRIC MOTOR

Abstract

A method and a device for estimating the torque ripple T.sub.TR of an electric motor connected to a load. An ideal rotational speed .sub.ideal of the electric motor is determined from an actuating torque T.sub.set_UUT for the electric motor. An output torque T.sub.shaft is measured at the load and a moment of mass inertia J of the electric motor in the controlled system of a control circuit. The ideal rotational speed .sub.ideal is adjusted by a controller of the control circuit on the basis of the real rotational speed .sub.UUT measured at the electric motor in such a way that the current torque ripple T.sub.TR is generated as a manipulated variable of the controller.

Claims

1-11. (canceled)

12. A method for estimating a torque ripple T.sub.TR of an electric motor connected to a load, the method comprising: determining an ideal rotational speed .sub.ideal of the electric motor from an actuating torque T.sub.set_UUT for the electric motor, an output torque T.sub.shaft measured at the load, and a moment of mass inertia J of the electric motor in a controlled system of a control circuit; and adjusting the ideal rotational speed .sub.ideal by a controller of the control circuit on a basis of a real rotational speed .sub.UUT measured at the electric motor to thereby generate a current torque ripple T.sub.TR as a manipulated variable of the controller.

13. The method according to claim 12, which comprises estimating the torque ripple of a permanent magnet synchronous machine.

14. The method according to claim 12, which comprises carrying out the method on a test bench.

15. The method according to claim 12, wherein the load is a controllable load.

16. The method according to claim 12, which comprises carrying out the method during an operation of a vehicle driven by the electric motor.

17. The method according to claim 12, which further comprises compensating for the torque ripple.

18. A device for estimating the torque ripple T.sub.TR of an electric motor connected to a load, the device comprising: a sensor for measuring a real rotational speed .sub.UUT of the electric motor; a sensor for measuring an output torque T.sub.shaft of the load; wherein a control circuit with: a controlled system configured to determine an ideal rotational speed .sub.ideal of the electric motor from an actuating torque T.sub.set_UUT of the electric motor, the output torque T.sub.shaft, and a moment of mass inertia J of the electric motor; and a controller configured to adjust the ideal rotational speed .sub.ideal on a basis of the real rotational speed .sub.UUT in such a way that the torque ripple T.sub.TR is generated as a manipulated variable of the controller.

19. The device according to claim 18, constituting a part of a test bench for an electric motor.

20. The device according to claim 18, wherein the load is a controllable load.

21. The device according to claim 18, constituting a part of a drive of a vehicle.

22. The device according to claim 18, wherein the electric motor is a permanent magnet synchronous machine.

Description

[0015] The invention is explained in more detail below on the basis of an exemplary embodiment example. In the drawing:

[0016] FIG. 1 shows a conventional setup of a test bench for an electric motor;

[0017] FIG. 2a-2c: show details of an embodiment of the system and method according to the invention.

[0018] FIG. 1 shows a conventional setup of a test bench for an electric motor 1. The electric motor 1 to be tested (test piece or Unit-Under-Test UUT) is connected to a controllable load 3 via a shaft 2. With a control unit 4 (not represented in this figure) of the load 3, various loading states are preset for the electric motor 1 to be tested, for example a presetting of the rotational speed to be achieved or the torque to be achieved. Such test benches are generally used without a transmission, drivetrain and other drive components.

[0019] In this figure, T.sub.set_UUT denotes the actuating torque and n.sub.UUT denotes the measured rotational speed at the electric motor 1 to be tested. The symbol T.sub.shaft denotes the output torque measured at the shaft 2. The rotational speed preset at the load 3 is denoted by the symbol T.sub.set_Dyno, and the rotational speed measured at the load 3 is denoted by the symbol n.sub.Dyno.

[0020] The rotational speed measured at the test piece can be used to perform a calculation of the torque ripple (ripple moment) T.sub.TR in a post-processing step, the previously determined moment of mass inertia J.sub.UUT of the electric motor 1 being used for this purpose:

[00001]$T_{\mathrm{TR}}=J_{\mathrm{UUT}}\left({\stackrel{.}{n}}_{\mathrm{UUT}}.Math.\frac{}{30}\right)-T_{{\mathrm{set}}_{\mathrm{UUT}}}+T_{\mathrm{shaft}}$

[0021] However, a differentiation of the measured rotational speed n.sub.UUT while operation is in progress is problematic and is usually only meaningfully possible with low-pass filtering of the signal.

[0022] FIG. 2a shows an ideal torque generator 4, which can be used as part of the method according to the invention. In this ideal torque generator 4, T.sub.set denotes the actuating torque, T.sub.shaft denotes the measured output torque, and .sub.ideal denotes the rotational speed of the ideal electric motor. The moment of mass inertia of the electric motor is denoted by the symbol J. The mathematical relationship is as follows:

[00002]${}_{\mathrm{ideal}}=\frac{1}{J}.Math.\left(T_{\mathrm{set}}-T_{\mathrm{shaft}}\right)$

[0023] For the calculation of the real rotational speed .sub.real, added to the actuating torque and the output torque is the unknown torque ripple (ripple moment) T.sub.TR:

[00003]${}_{\mathrm{real}}=\frac{1}{J}.Math.\left(T_{\mathrm{set}}-T_{\mathrm{shaft}}+T_{\mathrm{TR}}\right)$

[0024] Consequently, the ideal rotational speed .sub.ideal is equal to the real rotational speed .sub.real if, in addition to the actuating torque and the output torque, the ripple moment T.sub.TR is taken into account at the input of the ideal electric motor.

[0025] FIG. 2b shows a correspondingly designed control circuit 5, in which the ideal rotational speed .sub.ideal is adjusted as a controlled variable on the basis of the real measured rotational speed .sub.real as a reference variable. Provided for this purpose is a controller 6, which in the present embodiment example is designed as a PI controller. The controller 6 is fed the difference between the ideal rotational speed .sub.ideal and the real rotational speed .sub.real as a system deviation.

[0026] The controller 6 produces a torque deviation as a manipulated variable. In the controlled system, the current actuating torque T.sub.set and the measured output torque T.sub.shaft are subtracted from the manipulated variable, and the result is divided by the moment of mass inertia J and the time derivative is formed, so that the current rotational speed is formed as the controlled variable.

[0027] The output variable of the controller 6 consequently corresponds to the current torque ripple, that is to say the ripple moment T.sub.TR. The current torque ripple at a given time is consequently automatically obtained in this control circuit 5 as a byproduct of the speed control carried out.

[0028] FIG. 2c shows an embodiment of the invention in the example of a specific test bench. Once again, the electric motor 1 to be tested is connected to a controllable load 3 via a shaft 2. In this figure, T.sub.set_UUT again denotes the actuating torque of the electric motor 1 to be tested and .sub.UUT denotes the measured rotational speed at the electric motor 1 to be tested.

[0029] The controller 6 calculates from the difference of the rotational speed of the load 3 and the preset rotational speed .sub.dem_Load the setpoint torque T.sub.set_Load of the load 3.

[0030] Both the load 3 and the electric motor 1 to be tested 1 are activated by means of a driver unit 7, which converts the desired torque T.sub.set_Load and T.sub.set_UUT into corresponding activation signals for the load 3 and the electric motor 1, respectively. The symbol T.sub.shaft again denotes the output torque measured at the shaft 2.

[0031] As explained in connection with FIG. 2b, the current ripple moment T.sub.TR is determined in the control circuit 5 from T.sub.set_UUT, T.sub.shaft and the measured rotational speed .sub.UUT, without a differentiation of the current rotational speed of the electric motor being required.

[0032] The invention is not restricted to a specific design of the electric motor, the load or the control circuit, but comprises all methods and devices within the scope of the following patent claims.