Method for Operating an Electric Machine of a Motor Vehicle, System and Motor Vehicle

Abstract

A method is provided for operating a synchronous machine that can be operated in an efficient operating mode and an inefficient operating mode. In order to provide a working-point-specific torque the synchronous machine is controlled in the efficient operating mode such that a stator of the synchronous machine generates a synchronous rotary field which rotates synchronously with a rotor of the synchronous machine. In order to increase dissipated heat of the synchronous machine, which can be used to heat at least one component of the motor vehicle, the synchronous machine is transferred into the inefficient operating mode in which an asynchronous rotary field acts on the synchronous rotary field, said asynchronous rotary field superimposing dissipated heat-increasing harmonics on a fundamental wave of the synchronous rotary field while maintaining the working-point-specific torque.

Claims

1.-10. (canceled)

11. A method for operating an electric machine in a form of a synchronous machine of a motor vehicle, wherein the machine is operable in an efficient operating mode with optimum power losses and in an inefficient operating mode which increases power losses, the method comprising: in order to provide an operating-point-specific torque, controlling the synchronous machine in the efficient operating mode such that a stator of the synchronous machine generates a synchronous rotating field which rotates synchronously with a rotor of the synchronous machine; and in order to increase heat losses of the synchronous machine, wherein the heat losses are usable to heat at least one component of the motor vehicle, transferring the synchronous machine into the inefficient operating mode in which an asynchronous rotating field acts on the synchronous rotating field, wherein the asynchronous rotating field superposes heat-loss-increasing harmonics on a fundamental wave of the synchronous rotating field while maintaining the operating-point-specific torque.

12. The method according to claim 11, wherein the inefficient operating mode of the synchronous machine for increasing the heat losses is provided when the at least one component provides a heating requirement signal.

13. The method according to claim 11, wherein an angular speed of the asynchronous rotating field is different from an angular speed of the synchronous rotating field, such that a frequency of the harmonics is different from a frequency of the fundamental wave.

14. The method according to claim 13, wherein the frequency of the harmonics and the angular speed of the asynchronous rotating field are prescribed depending on a heating power required by the at least one component.

15. The method according to claim 13, wherein the frequency of the harmonics and the angular speed of the asynchronous rotating field are selected such that a noise of the synchronous machine resulting from the asynchronous field is below an uncomfortableness threshold of human hearing.

16. The method according to claim 15, wherein the uncomfortableness threshold of human hearing is a hearing threshold of human hearing.

17. The method according to claim 11, wherein: the synchronous machine for providing the operating-point-specific torque is controlled using a field-oriented control by prescribing a field-forming setpoint current and a torque-forming setpoint current in order to generate the synchronous rotating field, and at least one of the setpoint currents is superposed by a current harmonic in order to generate the asynchronous rotating field.

18. A system for a motor vehicle, the system comprising: the synchronous machine; the at least one component; and a control device which is configured to perform the method according to claim 11.

19. The system according to claim 18, further comprising: a cooling circuit which conveys coolant and to which the synchronous machine and the at least one component are connected, wherein: the control device is configured to provide the asynchronous rotating field for the synchronous machine when the at least one component provides a heating requirement signal, and the heat losses output by the synchronous machine are transportable via the coolant of the cooling circuit to the at least one component.

20. The system according to claim 18, wherein the at least one component is a traction battery and the synchronous machine is a traction machine of the motor vehicle.

21. A motor vehicle comprising the system according to claim 18.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a schematic illustration of an embodiment of a system comprising a synchronous machine in an efficient operating mode.

[0020] FIG. 2 shows the system according to FIG. 1 comprising the synchronous machine in an inefficient operating mode.

DETAILED DESCRIPTION OF THE DRAWINGS

[0021] Identical or functionally identical elements are provided with the same reference signs in the figures.

[0022] FIG. 1 and FIG. 2 each show a system 1 which comprises a synchronous machine 2 and a control device 3. The system 1 can be used in an electrically driveable motor vehicle in which the synchronous machine 2 serves as electric traction machine of the motor vehicle. The system 1 furthermore comprises at least one component 4 to be heated. The component 4 to be heated is in this case an electric traction battery 5 in the form of a high-voltage energy store which supplies electrical energy to the synchronous machine 2. The component 4 to be heated and the synchronous machine 2 are thermally coupled via a cooling circuit 6 which conveys coolant and is illustrated here only schematically. According to FIG. 1, the synchronous machine 2 is operated in an efficient operating mode in which the synchronous machine 2 outputs minimal power losses and thus heat losses. The efficient operating mode is provided whenever the component 4 to be heated has no heating requirement. According to FIG. 2, the synchronous machine 2 is operated in an inefficient operating mode in which the synchronous machine 2 has higher heat losses in comparison to the efficient operating mode. The inefficient operating mode is provided whenever the component 4 has a heating requirement. The component 4 is then supplied with the heat losses generated by the synchronous machine 2 by way of the coolant of the cooling circuit 6.

[0023] The control device 3 comprises an inverter 7 which is connected between the traction battery 5 and the synchronous machine 2. The inverter 7 is in particular likewise integrated into the cooling circuit 6 such that heating losses of the inverter 7 can additionally be transported to the component 4 to be heated. The inverter 7 is connected to three phase windings u, v, w of a stator of the synchronous machine 2. In order to be able to provide a required operating-point-specific torque M, the inverter 7 applies setpoint phase voltages u*.sub.u, u*.sub.v, u*.sub.w to the three phase windings u, v, w of the synchronous machine 2, by way of which setpoint phase voltages the phase windings are energized using phase currents i.sub.u, i.sub.v, i.sub.w. These phase currents i.sub.u, i.sub.v, i.sub.w generate a rotating field which sets a rotor of the synchronous machine 2 for providing the operating-point-specific torque M in rotation. The setpoint phase voltages u*.sub.u, u*.sub.v, u*.sub.w are determined by a controller 8 of the control device 3 based on setpoint currents i*.sub.q and i*.sub.d and actual currents i.sub.d, i.sub.q. The controller 8 operates in this case in a two-axis, rotor-oriented dq coordinate system. The actual currents i.sub.d, i.sub.q are a torque-forming actual current i.sub.q and a field-forming actual current i.sub.d, which are determined based on the measured actual phase currents i.sub.u, i.sub.v, i.sub.w. The measured actual phase currents i.sub.u, i.sub.v, i.sub.w are converted by way of coordinate transformation into the actual currents i.sub.d, i.sub.q. Since the dq coordinate system rotates at an angular speed ω of the rotor of the synchronous machine 2, the coordinate transformation is carried out taking into account a present measured rotor angle γ.

[0024] Since in the present synchronous machine 2 the usable torque M is generated only when the magnetic rotating field rotates synchronously with the rotor, that is to say when an angular speed of the synchronous rotating field rotates at the angular speed ω of the rotor, the setpoint phase voltages u*.sub.u, u*.sub.v, u*.sub.w are determined depending on the change in the rotor angle γ with respect to time, which corresponds to the angular speed ω of the rotor. These setpoint phase voltages u*.sub.u, u*.sub.v, u*.sub.w are converted into control signals for the inverter 7. The setpoint currents i*.sub.q and i*.sub.d are in this case determined in such a way that the required torque M is generated. The torque M is generated using

M=3/2p(Ψ.sub.di*.sub.q−Ψ.sub.qi*.sub.d)

[0025] with the number of pole pairs ρ, the flux linkage ψ.sub.d along the d-axis and the flux linkage along the q-axis.

[0026] In this case, there are different combinations of the setpoint currents i*.sub.q, i*.sub.d which generate the same torque M. In the efficient operating mode, the values of the setpoint currents i*.sub.q, i*.sub.d are selected in such a way that an amplitude of the current I=√{square root over (i.sub.q*+i.sub.d*)} is minimal.

[0027] In order to provide the inefficient operating mode, the synchronous rotating field is superposed by an asynchronous rotating field. The angular speed of the asynchronous rotating field is in this case different to, for example significantly greater than, the angular speed ω of the rotor, which also corresponds to the angular speed of the synchronous rotating field. The angular speed of the asynchronous rotating field can also be lower than the angular speed ω of the rotor. The asynchronous rotating field is generated by virtue of the setpoint currents i*.sub.q and i*.sub.d being superposed by harmonics Δi.sub.d, Δi.sub.q. Δi.sub.d, Δi.sub.q can be calculated for example using:

Δi.sub.d=Im*sin(ω.sup.2t)

Δi.sub.q=Im*cos(ω.sup.2t)

[0028] These harmonics Δi.sub.d, Δi.sub.q superpose harmonics which generate iron losses and thus increased heat losses on a fundamental wave of the synchronous rotating field. The resulting torque M+ΔM is calculated using

M+ΔM=3/2p(Ψ.sub.d(i*.sub.q+Δi.sub.q)−Ψ.sub.q(i*.sub.d+Δi.sub.d),

[0029] wherein ΔM are harmonics in the torque M which are able to be damped by way of the motor vehicle. The heat losses generated by Δi.sub.d, Δi.sub.q are supplied to the component 4 to be heated. In the inefficient operating mode, the synchronous machine 2 thus functions as a heating device for the component 4.