Method for operating an electric machine

Abstract

The invention relates to a method for operating an electric machine (6), and to a control device (10) that is configured to carry out the method. The method comprises a normal mode (ψ.sub.normal) and a special mode (ψ.sub.special) in dependence on a preset target value (M.sub.target), wherein the normal mode (ψ.sub.normal) comprises the steps of detecting an operating state, wherein, in the event that the detected operating state is a special state, the special mode (ψ.sub.special) is carried out. The special mode (ψ.sub.special) comprises the steps of modulating a cyclic value (M.sub.cysl) on the present target value (M.sub.target) and detecting the operating state, wherein, in the event that the operating state is a normal state, the normal mode (ψ.sub.normal) is carried out.

Claims

1. A method for operating an electric machine (6), wherein the method comprises a normal operating mode (ψ.sub.Normal) and a special operating mode (ψ.sub.Special) depending on a preset setpoint value (M.sub.Set), and wherein the normal operating mode (ψ.sub.Normal) comprises the steps of: detecting an operating state, wherein when the detected operating state is a special state, the special operating mode (ψ.sub.Special) is implemented, wherein the special operating mode (ψ.sub.Special) comprises the steps of: modulating a cyclical value (M.sub.Cycl) onto the preset setpoint value (M.sub.Set), detecting the operating state, wherein when the operating state is a normal state, the normal operating mode (ψ.sub.Normal) is implemented.

2. The method for operating an electric machine (6) as claimed in claim 1, wherein the cyclical value (M.sub.Cycl) is modulated in such a way that a cyclical movement of the rotor of the electric machine (6) results which has an amplitude which is greater than ⅙ of an electrical revolution.

3. The method for operating an electric machine (6) as claimed in claim 1, wherein the frequency of the cyclical value (M.sub.Cycl) is selected such that it is in the vicinity of or equal to a natural frequency of a dynamic system that includes a machine controller, power electronics (17), the electric machine (6) and/or a downstream mechanical drive system, with the result that the desired amplitude of the cyclical movement of the rotor position is achieved given a reduced amplitude of the cyclical value (M.sub.Cycl).

4. The method for operating an electric machine (6) as claimed in claim 1, wherein a setpoint torque (M.sub.Set) is used as setpoint value.

5. The method for operating an electric machine (6) as claimed in claim 1, wherein a setpoint current of a current controller of the electric machine (6) is used as setpoint value.

6. The method for operating an electric machine (6) as claimed in claim 1, wherein a setpoint angle of the rotor of the electric machine (6) is used as setpoint value.

7. The method for operating an electric machine (6) as claimed in claim 1, wherein the reaching of the special state is detected when the rotational frequency of the electrical voltage phasor impressed by power electronics (17) is less than a limit frequency, and a temperature (T.sub.Limit), a phase current and/or a resultant torque exceeds a threshold value.

8. The method for operating an electric machine (6) as claimed in claim 7, wherein the special state is detected only after a predetermined time period during which a threshold value is exceeded.

9. The method for operating an electric machine (6) as claimed in claim 7, wherein the limit frequency is fixed depending on the thermal properties of the power electronics (17).

10. The method for operating an electric machine (6) as claimed in claim 7, wherein the leaving of the special state is detected when the rotational frequency of the electrical voltage phasor impressed by the power electronics (17) is greater than the limit frequency.

11. A closed-loop control device (10) for operating an electric machine (6), wherein the closed-loop control device (10) comprises: a setpoint value presetting unit (14), for presetting a setpoint value (M.sub.Set), a signal conditioner (15), for the closed-loop control of the electric machine (6), power electronics (17) configured as an actuating element for the electric machine (6), an operating state detection and decision unit (18), for detecting an operating state and for deciding whether, on the basis of the operating state, a special operating mode (ψ.sub.Special) or a normal operating mode (ψ.sub.Normal) should be implemented, and a modulation unit (26), for modulating a cyclical value (M.sub.Cycl) onto the setpoint value (M.sub.Set) during the special operating mode (ψ.sub.Special).

12. The closed-loop control device (10) as claimed in claim 11, wherein the electric machine (6) is a synchronous machine.

13. A non-transitory, computer-readable medium containing instructions that when executed by a computer cause the computer to control an electric machine to detect an operating state, and when the detected operating state is a special state, implement a special operating mode (ψ.sub.Special) by modulating a cyclical value (M.sub.Cycl) onto a preset setpoint value (M.sub.Set), and when the detect operating state is a normal state, implement a normal operating mode (ψ.sub.Normal).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the description below. In the drawings:

(2) FIG. 1 shows an exemplary embodiment of a method for operating an electric machine and closed-loop control device for performing the method, and

(3) FIG. 2 shows a graph for illustrating an exemplary embodiment of the method according to the invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows an exemplary embodiment of a method for operating an electric machine 6 and a closed-loop control device 10 for performing the method. The closed-loop control device 10 in this case comprises a setpoint value presetting unit 14, which, during a normal operating mode ψ.sub.Normal, passes on the setpoint value, which in this case is a setpoint torque M.sub.Set, for example, to a signal conditioner 15, consisting of a machine controller, a transformation into the rotating coordinate system, and a phasor pulse width modulation, which adjusts the torque of the electric machine 6 having power electronics 17 as actuating element to the setpoint value M.sub.Set. In another exemplary embodiment, the setpoint value can likewise be a setpoint current of a current controller.

(5) The closed-loop control device 10 additionally comprises an operating state detection and decision unit 18, which detects an operating state M.sub.Act of the electric machine 6 and the power electronics 17. The operating state detection and decision unit 18 determines the present operating state of the drive, wherein the state variables of the drive are M.sub.Act or M.sub.Set, the position and rotational frequency of the rotor, the temperatures of the switches in the power electronics 17 and possibly further state variables. If the rotational frequency of the electrical voltage phasor impressed by the power electronics 17 falls below a limit frequency and, in addition, the temperature T.sub.Limit of the switches of the power electronics 17, a current and/or a torque exceeds a threshold, above a threshold value, the decision unit in the operating state detection and decision unit 18 switches to a special operating mode ψ.sub.Special.

(6) During the special operating mode ψ.sub.Special, a modulation unit 26 modulates a cyclical value M.sub.Cycl onto the setpoint value M.sub.Set. Owing to generally sufficiently pronounced elasticities in the drive, the modulated fluctuations in the torque result in cyclical movements of the rotor of the electric machine 6, which result in the switching cycles in the power electronics 17 being more uniformly distributed among the individual component parts. As a result, one-sided thermal loading of the component parts is reduced. The special operating mode ψ.sub.Special is left again, and the normal operating mode ψ.sub.Normal is implemented again when the decision unit in the operating state detection and decision unit 18 receives the signal that the electrical rotational frequency of the rotor is above the limit frequency.

(7) FIG. 2 shows a graph for illustrating an exemplary embodiment of the method according to the invention. In this graph, the setpoint torque M.sub.Set is plotted over time t. In addition, a rotor angle θ.sub.R or the integral of the speed of the rotor is plotted over time t. It can be seen from the two curves that, despite the rise in the setpoint torque M.sub.Set, the rotor angle θ.sub.R after an initial rise remains relatively constant at one level.

(8) In addition, the graph shows that a temperature curve T, which shows the temperature in at least one of the switch branches, rises above a limit value T.sub.Limit. As a result, a special operating mode ψ.sub.Special is implemented in which a cyclical value M.sub.Cycl is modulated onto the setpoint value M.sub.Set. This can be seen in FIG. 2 as an oscillation in the setpoint value M.sub.Set and oscillation in the rotor angle θ.sub.R. Owing to the oscillation in the rotor angle θ.sub.R, the individual switch branches are subjected to a more uniform load, with the result that a further temperature rise T, as shown in FIG. 2, can be avoided. The temperature T is maintained more or less at a constantly high level.

(9) Owing to the increase in the driver's desired torque, the mean rotor angle θ.sub.Rm increases continuously, which results in the transition to a rotary movement and therefore to the normal operating mode ψ.sub.Normal. The characteristic illustrated in FIG. 2 is typical for a traction drive of an electric or hybrid vehicle which is initially stationary for a time on an incline, wherein the state of equilibrium is held by the electric drive, and then a vehicle starting operation follows by further depression of the gas pedal.

(10) A further example is a stationary state of the vehicle at an obstacle, for example a curb, in which, by activation of the gas pedal, the wheels first press for a time against the curb and then, by further depression of the gas pedal, a vehicle starting operation takes place in which the obstacle is overcome.