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

Description

[0001] The invention relates to a method and a device for estimating the torque ripple of an electric motor.

[0002] Electric motors, especially permanent magnet synchronous motors (PMSMs), are widely used in the automotive sector. These electric motors are typically used in conjunction with a gearbox and drive shafts to the drive wheels as a drivetrain. Such a drivetrain represents a complex mechanical system with structural and torsional eigenmodes. The occurrence of periodic excitations at frequencies close to the frequencies of these eigenmodes can cause unpleasant noise for the driver. This can also impact component service life, even leading to the destruction of individual drivetrain components.

[0003] A typical side effect of using such electric motors is the occurrence of torque ripple, also known as "torque ripple." This refers to a torque distribution across the rotation angle of the electric motor's rotor that is slightly dependent on the angle of rotation. Causes can include an uneven distribution of the motor winding, inhomogeneities in the permanent magnets, or even asymmetries in the electronic components used.

[0004] Typically, these torque ripples occur in orders of the rotational frequency, where the order number is determined, for example, by the number of pole pairs and the number of slots.

[0005] Another typical side effect is the occurrence of so-called cogging torque in such motors. Cogging torque refers to the torque ripple of the de-energized electric motor.

[0006] To accurately measure the torque ripple, it is advantageous to measure the torque at the electric motor's output shaft. However, torque measurement is usually not provided in electric motor-gearbox systems, or it is technically difficult to implement.

[0007] Using a test bench where the electric motor's output torque is measured, for example, via a measuring flange, the torque ripple can also be calculated in a post-processing step. However, this requires measuring and differentiating the electric motor's speed. This is problematic during operation and is usually only possible by low-pass filtering the measurement signal, which is complex and highly error-prone.

[0008] US Pat. No. 5,534,764 A discloses a method for estimating the vibrations of a vehicle's drivetrain or drive shaft during operation using a vehicle system model. However, this method does not take into account the torque ripple of the driving electric motor. WO 2009 / 034024 A2 describes a test bench for an electric or mechanical drive. EP 2 447 120 A2 describes a vehicle control system for a hybrid vehicle.

[0009] One object of the invention is therefore, inter alia, to provide a method and a device by means of which torque ripples of an electric motor can be estimated as accurately as possible on the test bench and during operation.

[0010] These and other objects are achieved according to the invention by a method according to patent claim 1. The method according to the invention estimates the torque ripple T TR of an electric motor connected to a load from a setting torque T set_UUT for the electric motor, an output torque T shaft measured at the load and the known mass moment of inertia J of the electric motor by forming a control loop for tracking the speed of the electric motor. In the control system of the control loop, the ideal speed ω ideal of the electric motor is determined and the controller of the control loop tracks this ideal speed ω ideal to the real speed ω UUT measured at the electric motor in such a way that the current torque ripple T TR appears as a manipulated variable at the output of the controller. The manipulated variable can then be fed out and tapped.

[0011] The controller can, in particular, be designed as a PI controller. The method according to the invention can be used to estimate the torque ripple of a permanent magnet synchronous machine. The method can advantageously be used both on a test bench and directly in a vehicle. The load can be a controllable load. The method can also be used during operation of a vehicle driven by an electric motor, provided the measured variables of speed and shaft torque are known. This is advantageous because it allows the torque ripple to be estimated in real time, eliminating the need for a complex post-processing step. Furthermore, no differentiation of the measured motor speed is necessary.

[0012] The invention also extends to a device for estimating the torque ripple T TR of an electric motor connected to a load via a shaft. The device according to the invention comprises a sensor for measuring the actual speed ω UUT of the electric motor and a sensor for measuring the output torque T shaft of the load.

[0013] The device further comprises a control loop for tracking the speed of the electric motor, comprising a control system and a controller. In the control system, an ideal speed ω ideal of the electric motor is determined from a setting torque T set_UUT of the electric motor, the output torque T shaft , and a mass moment of inertia J of the electric motor. The controller is designed to track the ideal speed ω ideal to the actual speed ω UUT in such a way that the torque ripple T TR is generated as the controller's manipulated variable. This manipulated variable can then be fed to the outside and tapped.

[0014] According to the invention, the device can be part of a test bench for an electric motor. According to the invention, the electric motor can be a permanent magnet synchronous motor, an asynchronous motor, or a reluctance motor. The load can be a controllable load. However, the device can also be part of the drive system of a vehicle.

[0015] Further features of the invention emerge from the patent claims, the description of the embodiments and the drawings.

[0016] The invention will be explained in more detail below using an exemplary embodiment. Fig. 1 : a conventional test bench setup for an electric motor; Fig 2a - 2c : Details of an embodiment of the system and method according to the invention.

[0017] Fig. 1 shows a conventional test bench design for an electric motor 1. The electric motor 1 to be tested (unit under test or UUT) is connected to a controllable load 3 via a shaft 2. A control unit 4 of the load 3 (not shown in this figure) specifies different load conditions for the electric motor 1 to be tested, for example, a specification of the desired speed or torque. Such test benches are generally used without a transmission, drive train, or other drive components.

[0018] In this figure, T set_UUT denotes the set torque and n UUT denotes the measured speed of the electric motor 1 under test. The symbol T shaft denotes the output torque measured at shaft 2. The torque set at load 3 is denoted by the symbol T set_Dyno , and the speed measured at load 3 is denoted by the symbol n Dyno .

[0019] From the speed measured on the test object, the torque ripple T TR can be calculated in a post-processing step, using the previously determined mass moment of inertia J UUT of the electric motor 1: T TR = J UUT n ˙ UUT π 30 − T set UUT + T shaft

[0020] However, differentiating the measured speed n UUT during operation is problematic and usually only possible with low-pass filtering of the signal.

[0021] Fig.2a shows an ideal torque generator 4 that can be used as part of the method according to the invention. In this ideal torque generator 4, T set denotes the actuating torque, T shaft the measured output torque, and ω ideal the speed of the ideal electric motor. The symbol J denotes the mass moment of inertia of the electric motor. The mathematical relationship is: ω ideal = 1 J ∫ T set − T shaft

[0022] To calculate the real speed ω real, the unknown torque ripple T TR is added to the actuating torque and output torque: ω real = 1 J ∫ T set − T shaft + T TR

[0023] Thus, the ideal speed ω ideal becomes equal to the real speed ω real if the ripple torque T TR is taken into account at the input of the ideal electric motor in addition to the actuating torque and the output torque.

[0024] Fig. 2b shows a correspondingly designed control loop 5, in which the ideal speed ω ideal as the controlled variable is tracked to the actual measured speed ω real as the reference variable. For this purpose, a controller 6 is provided, which in the present embodiment is designed as a PI controller. The difference between the ideal speed ω ideal and the actual speed ω real is fed to the controller 6 as the control deviation.

[0025] Controller 6 provides a torque deviation as the manipulated variable. In the controlled system, the current actuating torque T set and the measured output torque T shaft are subtracted from the manipulated variable. The result is divided by the mass moment of inertia J, and the integration over time is calculated, resulting in the current speed as the controlled variable.

[0026] The output variable of controller 6 thus corresponds to the current torque ripple, i.e., the ripple torque T TR . The current torque ripple is thus automatically generated in this control loop 5 as a by-product of the controlled speed control.

[0027] Fig. 2c shows an embodiment of the invention using the example of a specific test bench. Again, the electric motor 1 to be tested is connected to a controllable load 3 via a shaft 2. In this figure, T set_UUT again denotes the actuating torque of the electric motor 1 to be tested, and ω UUT denotes the measured speed of the electric motor 1 to be tested.

[0028] The controller 6' calculates the target torque T set_Load of the load 3 from the difference between the speed of the load 3 and the specified speed ω dem_Load. Both the load 3 and the electric motor 1 to be tested are controlled via a driver unit 7, which converts the desired torque T set_Load and T set_UUT into corresponding control signals for the load 3 and the electric motor 1, respectively. The symbol T shaft again denotes the output torque measured at the shaft 2.

[0029] From T set_UUT , T shaft and the measured speed ω UUT, as in connection with Fig. 2bexplained, the current ripple torque T TR is determined in control loop 5 without the need to differentiate the current speed of the electric motor.

[0030] The invention is not limited to a specific design of the electric motor, the load, or the control circuit, but encompasses all methods and devices within the scope of the following patent claims.

Claims

1. A method for estimating the torque ripple TTR of an electric motor (1) connected to a load (3), wherein the ideal rotational speed ωideal of the electric motor (1) is determined from an actuating torque Tset_UUT for the electric motor (1), an output torque Tshaft measured at the load (3) and a mass moment of inertia J of the electric motor (1) in the control path of a control loop (5), wherein the ideal rotational speed ωideal is lead to follow the real rotational speed ωUUT measured on the electric motor (1) by means of the controller (6) of the control loop (5) in such a way that the current torque ripple TTR is generated as a control variable of the controller (6), wherein the current torque ripple TTR is fed to the outside and tapped, characterised in that - the method is used on a test stand for the electric motor (1), and - the ideal rotational speed ωideal of the electric motor (1) is determined by subtracting the current control torque Tset and the measured output torque Tshaft from the control torque Tset_UUT and dividing the result by the mass moment of inertia J and integrating over time.

2. The method according to claim 1, characterised in that the method is used to estimate the torque ripple of a permanent magnet synchronous machine.

3. The method according to claim 1 or 2, characterised in that the load (3) is a controllable load (3).

4. The method according to any one of claims 1 to 3, characterised in that the method is used for torque ripple compensation.

5. A device for estimating the torque ripple TTR of an electric motor (1) connected to a load (3), comprising a sensor for measuring the real rotational speed ωUUT of the electric motor (1) and a sensor for measuring the output torque Tshaft of the load (3), wherein the device comprises a control loop (5), wherein the control loop (5) a. comprises a control path in which an ideal rotational speed ωideal of the electric motor (1) is determined from an actuating torque Tset_UUT of the electric motor (1), the output torque Tshaft and a mass moment of inertia J of the electric motor (1), b. and comprises a controller (6) which leads the ideal rotational speed ωideal to follow the real rotational speed ωUUT in such a way that the torque ripple TTR is generated as a control variable of the controller (6), wherein the current torque ripple TTR is fed to the outside and tapped, characterised in that - the device is part of a test stand for the electric motor (1), and - the control loop (5) is designed to determine the ideal rotational speed ωideal of the electric motor by subtracting the current control torque Tset and the measured output torque Tshaft from the control torque Tset_UUT and dividing the result by the mass moment of inertia J and integrating over time.

6. The device according to claim 5, characterised in that the load (3) is a controllable load (3).

7. The device according to claim 5 or 6, characterised in that the electric motor (1) is a permanent magnet synchronous machine.