Overvoltage arrester for an electrical drive

1. An overvoltage arrester for an electrical drive, said arrester configured to

be connected to an on-board power supply system of a motor vehicle,

to be connected to a control unit for an electronically-commutated electrical machine, and

to reduce overvoltage produced in the on-board power supply system when a load is switched off, said overvoltage arrester comprising:

an input for an on-board power supply system, the overvoltage arrester configured to

detect when a pre-determined overvoltage value is exceeded and to produce an overvoltage signal depending on whether the overvoltage value is exceeded, wherein the control unit is designed to transition the electrical machine, in response to receiving the overvoltage signal, from an operating mode in which the electrical machine generates power to at least one other mode selected from the group of a partial power-loss mode to dissipate electrical power as heat and a motor operating mode to dissipate electrical power as a mechanical torque,

and wherein the control unit is designed, as a function of the overvoltage signal, to reduce an exciting current through an excitation coil of the electrical machine via a semiconductor component connected to the excitation coil.

2. The overvoltage arrester according to claim 1 , wherein the overvoltage arrester has at least one semiconductor circuit breaker connected to the input, said semiconductor circuit breaker being designed, as a function of a pre-determined voltage value, to generate a current from the input via the semiconductor circuit breaker towards a ground terminal and thus reduce the on-board power supply system voltage.

3. The overvoltage arrester according to claim 1 , wherein the control unit is designed to actuate the electrical machine for the generation of a rotating magnetic field and to change a phase angle of the actuation of the electrical machine as a function of the overvoltage signal, and to operate the electrical machine at least partially in the power-loss mode and/or in the motor operating mode.

4. The overvoltage arrester according to claim 3 , wherein the control unit is designed, as a function of the overvoltage signal, to reduce a phase angle of the actuation of the electrical machine.

5. The overvoltage arrester according to claim 4 , wherein the control unit is designed, as a function of the overvoltage signal, to dispose of an angular difference between a rotor angle and a rotating field generated by the stator of the electrical machine.

6. The overvoltage arrester according to claim 3 , wherein the control unit is designed, as a function of the overvoltage signal, to change an angular difference between a rotor angle and a rotating field generated by the stator of the electrical machine in such a way that the electrical machine can be transferred from the generator operating mode to the full motor operating mode.

7. The overvoltage arrester according to claim 6 , wherein the control unit is designed to actuate the electrical machine in a pulse width modulated manner by means of the pulse width modulator, and the control unit is designed to invert an actuation model generated by a pulse width modulator of said control device as a function of the overvoltage signal.

8. The overvoltage arrester according to claim 3 , wherein the control unit is designed, as a function of the overvoltage signal, to reverse the polarity of an excitation coil of the electrical machine by means of a semiconductor switch connected to the excitation coil.

9. A method for operating an overvoltage protection for an on-board power supply system of a motor vehicle having an electrical machine, the method comprising:

during a generator operating mode of the electrical machine, determining whether a pre-determined overvoltage value of an on-board power supply system voltage has been exceeded,

generating an overvoltage signal in response to detecting that the pre-determined overvoltage value has been exceeded, wherein, a rapid de-excitation of an excitation magnetic field of the electrical machine is introduced as a function of the overvoltage signal,

reducing, with a control unit and via a semiconductor component connected to an excitation coil of the electrical machine, an exciting current through the excitation coil of the electrical machine as a function of the overvoltage signal;

detecting a temporal rise in the on-board power supply system voltage; and

changing, as a function of the rise in voltage, a phase angle of an actuation of the electrical machine in such a way that the electrical machine is transitioned from a generator operating mode to a motor operating mode by inverting a pulse width modulated actuation model.