METHOD FOR CONTROLLING THE OPERATION OF AN ELECTRIC MACHINE

Abstract

A method for controlling the operation of an electric machine, particularly an electric machine of a motor vehicle, wherein the electric machine is controlled to generate torque based on alternating current produced by a control device from a direct current supplied by an electrical energy storage. A function current which is determined depending on an actual operating point of the electric machine and which reduces a waviness of the direct current is impressed on the alternating current.

Claims

1. A method for controlling operation of an electric machine, comprising: controlling the electric machine to generate torque based on alternating current produced by a control device from a direct current supplied by an electrical energy storage; and determining a function current depending on an actual operating point of the electric machine and which reduces a waviness of the direct current is impressed on the alternating current.

2. The method according to claim 1, wherein a function current with a defined function parameter is generated for at least one operating point.

3. The method according to claim 1, wherein a set of function parameters is determined for at least one operating point by varying at least one function parameter.

4. The method according to claim 1, wherein in order to determine a set of function parameters in an evaluation run, a function current is generated with a first amplitude and a phase of the function current is changed in the evaluation run, wherein a phase is determined depending on a detection of the direct current and/or depending on a waviness of the direct current, and its amplitude is increased to a second amplitude.

5. The method according to claim 4, wherein the direct current and/or the waviness of the direct current is detected in an operating state of the electric machine, and at least one function parameter of the function current is determined depending on the detected direct current and/or the detected waviness of the direct current.

6. The method according to claim 4, wherein the direct current and/or the waviness of the direct current and an oscillation state of the electric machine are detected in a test state of the electric machine, particularly on a test stand, and at least one function parameter of the function current is determined depending on the detected direct current and/or the detected waviness of the direct current and the oscillation state.

7. The method according to claim 1, wherein at least one function parameter of the function current is determined in a model-based manner.

8. The method according to claim 7, wherein the at least one function parameter of the function current is determined depending on at least one oscillation parameter of a mechanical oscillation of the electric machine.

9. A drive arrangement for a motor vehicle, comprising: a control device; and an electrical energy storage configured to provide direct current and an electric machine, wherein the control device is configured to control the electric machine to generate torque based on alternating current generated from the direct current, wherein the control device is configured to impress a function current determined depending on an actual operating point of the electric machine on the alternating current, which function current reduces a waviness of the direct current.

10. Motor vehicle comprising: a drive arrangement comprising: a control device; and an electrical energy storage configured to provide direct current and an electric machine, wherein the control device is configured to control the electric machine to generate torque based on alternating current generated from the direct current, wherein the control device is configured to impress a function current determined depending on an actual operating point of the electric machine on the alternating current, which function current reduces a waviness of the direct current.

11. The method according to claim 1, wherein the electric machine is an electric machine of a motor vehicle.

12. The method according to claim 1, wherein two function currents with different function parameters are generated for at least two operating points.

13. The method according to claim 3, wherein the at least one function parameter that is varied is one or more of a phase and/or amplitude of the function current, based on a detection of the direct current and/or a waviness of the direct current and/or at least one oscillation parameter.

Description

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0025] The drawing shows a schematic diagram of a drive arrangement 1, for example, for a motor vehicle. Accordingly, a corresponding motor vehicle can have the drive arrangement 1. The drive arrangement 1 has an electric machine 2 which, for example, is formed as a traction drive for the motor vehicle or is used as a traction drive in the drive arrangement 1. In particular, this means that the electric machine 2 can be used to generate torque that can be utilized, for example, for the propulsion of the motor vehicle. The drive arrangement 1 further has a control device 3, which can be constructed, for example, as an inverter. The control device 3 controls the operation of the electric machine 2 by generating an alternating current. In other words, depending on an actual operating state or operating point of the electric machine 2, the control device 3 can generate a corresponding alternating current and supply it to the electric machine 2.

[0026] In order to provide energy, the drive arrangement 1 has an electrical energy storage 4 supplying the direct current. In other words, the control device 3 can be supplied with direct current from the electrical energy storage 4 to generate alternating current for controlling the electric machine 2. Further, the control device 3 is configured to generate a function current in addition to the alternating current and to supply it to the electric machine 2. The function current is selected such that a waviness of the direct current or DC current which is provided by the electrical energy storage 4 is reduced relative to an operating state of the drive arrangement 1 in which only the alternating current is generated.

[0027] In other words, alternating current refers to that part of the output signal of the control device 3 to the electric machine 2 that is required for achieving the desired operating state, for example, to adopt a defined operating point of the electric machine 2 that defines itself, for example, from a determined speed and/or a determined torque. In addition to this, the function current which ultimately has no influence on the operating state but reduces the waviness or DC ripple in the direct current provided by the electrical energy storage 4 is outputted.

[0028] The described function current can be adjusted in any desired manner in principle, for example, as any component or combination of d-current and/or q-current, for example, comprising exclusively d-current or q-current. To this end, for example, the control device 3 can also adjust one or more function parameters of the function current, for example, the phase, amplitude or frequency thereof. As has been described, a function current can be generated for at least one operating point of the electric machine 2. Specifically, two different function currents, i.e., function currents with different function parameters or different sets of function parameters, can be generated for at least two operating points. In this regard, any number of operating points and/or function currents can be formed in principle and stored in the control device 3 so that the control device 3 generates the appropriate function current and can supply it to the electric machine 2.

[0029] In order to find the correct function current or function parameter for an operating point, at least one function parameter of a set of function parameters of the function current can be varied, for example. For example, the phase and/or the amplitude of the function current can be varied. The effects of generating the function current can be detected by suitable sensors. For example, detection can be carried out during operation or on a test stand. The drive arrangement 1 can be coupled with various sensors for this purpose or can have such sensors. By way of example, a current sensor 5 is shown, which is configured to detect at least one electrical parameter of the direct current, for example, the direct current itself and/or the waviness of the direct current. Accordingly, it can be determined whether or not impressing the function current in addition to the alternating current achieves the desired effect, that is, whether or not the waviness of the direct current is reduced in the desired manner by the adjusted function current.

[0030] Optionally, an oscillation sensor 6 or a plurality of oscillation sensors can be provided, for example, in the form of an acceleration sensor, which can be coupled with the electric machine 2. For example, such oscillation sensors 6 can be provided on a test stand and can determine which mechanical oscillations are generated or excited by the electric machine 2 in various operating points of the electric machine 2. The generated oscillations can also be determined in relation to the generated function current. Specifically, a best point can be found at which the best possible reduction of the waviness of the DC current and lowest possible excitation of mechanical oscillations or reduction of mechanical oscillations is achieved.

[0031] An evaluation run in which a set of function parameters for the function current is determined for at least one operating point can be carried out, for example, on a test stand or in an operating state of the drive arrangement 1. The evaluation run may be repeated for a plurality of operating points of the electric machine 2, for example, various speeds and/or torques. The results of the evaluation run can be stored in the control device 3 and correspondingly retrieved when an operating point is occupied by the electric machine 2 so that the function current stored for the operating point can be adjusted.

[0032] During the evaluation run, the function current can initially be generated with a first amplitude which can be comparatively low in order to minimize as far as possible the effects of impressing the function current. Subsequently, the phase of the function current can be changed in the evaluation run, and the effects of impressing the function current can be detected. As has already been described, the at least one electrical parameter of the direct current and/or the waviness of the direct current can be detected, for example. The changes or effects of the function current on the oscillation state of the electric machine 2 can also be detected. If a suitable set of function parameters is found for the function current, the first amplitude can be increased or reduced to a second amplitude for this operating point in order to strengthen the effect of the function current or to select the desired amplitude.

[0033] In addition to the direct detection of effects or the direct detection of the direct current or of oscillations by the current sensor 5 or by the oscillation sensor 6, respectively, the at least one function parameter of the function current can also be determined based on a model. To this end, a model of the waviness of the direct current can be stored on the control device 3. Accordingly, the model can display the expected waviness of the direct current for various operating states of the electric machine 2 so that the control device 3 is capable of adjusting the at least one function parameter of the function current in such a way that a desired reduction of waviness is achieved. The method described herein can be implemented on the drive arrangement 1. The description is transferrable in a corresponding manner.

[0034] Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.