Method for operating power semiconductors

1. A method for operating power semiconductors arranged in converters, comprising:

measuring with a temperature sensor a temperature of at least one of the power semiconductors;

performing a comparison of the temperature of the at least one power semiconductor with a reference temperature and providing a result of the comparison;

activating a pre-heating phase for preheating the power semiconductors as a function of the result, said pre-heating phase being activated resulting in an increase in I HEAT when the result indicates that the temperature of the at least one power semiconductor is lower than the reference temperature and a collector current I C is dropped to a value approximating zero, and wherein the pre-heating phase is not activated when the result indicates that the temperature of the at least one power semiconductor is greater than or equal to the reference temperature, wherein a duration of the pre-heating phase lies within a range of seconds;

during the pre-heating phase, defining a pre-heating current; and

impressing the pre-heating current into an electrical load.

2. The method of claim 1 , wherein the power semiconductors are arranged on an intermediate DC circuit of the converters.

3. The method of claim 1 , wherein the electrical load is an electric machine connected to the power semiconductors.

4. The method as of claim 1 , further comprising performing a further comparison of the temperature of the at least one power semiconductor with a further reference temperature and providing a further result of the further comparison.

5. The method of claim 1 , wherein the duration of the pre-heating phase is within a range of up to one second.

6. The method of claim 1 , wherein, during an activated state of the pre-heating phase, the pre-heating current is impressed into the electric machine, and wherein the pre-heating current generates no torque in the electric machine.

7. The method of claim 1 , wherein the pre-heating current generates no torque on a shaft of the electric machine.

8. The method of claim 1 , wherein the electric machine is operated with a torque, which acts on a mechanical shaft of the electric machine, and wherein during an activated state of the pre-heating phase the pre-heating current is impressed into the electric machine.

9. The method of claim 4 , wherein the pre-heating phase, when activated in the activating step, remains active when the further result indicates that the temperature of the at least one power semiconductor is lower than the further reference temperature, and wherein the pre-heating phase when activated in the activating step is deactivated when the further result indicates that the temperature of the at least one power semiconductor is greater than or equal to the further reference temperature.

10. The method of claim 6 , wherein the electric machine is constructed as an asynchronous machine and the pre-heating current is impressed into the asynchronous machine during the pre-heating phase by means of a magnetization current.

11. The method of claim 6 , wherein the electric machine is a synchronous machine and the pre-heating current is impressed into the synchronous machine during the pre-heating phase by means of a field-forming current.

12. The method of claim 7 , wherein the pre-heating current is provided as a function of a vector control.

13. The method of claim 8 , wherein the pre-heating current is provided as a function of a vector control.

14. The method of claim 10 , wherein the magnetization current is a current component of a vector control for asynchronous machines.

15. The method of claim 11 , wherein the field-forming current is a current component of a vector control for synchronous machines.

16. A computing unit, comprising:

a temperature input unit for receiving a measured temperature of at least one of a plurality of power semiconductors arranged in converters of an electric machine; and

a signal output unit,

said computing unit being configured

to perform a comparison of the measured temperature with a reference temperature and to provide a result of the comparison,

to activate a pre-heating phase for preheating the power semiconductors as a function of the result, said pre-heating phase being activated resulting in an increase in I HEAT when the result indicates that the temperature of the at least one power semiconductor is lower than the reference temperature and a collector current I C is dropped to a value approximating zero, and wherein the pre-heating phase is not activated when the result indicates that the temperature of the at least one power semiconductor is greater than or equal to the reference temperature, wherein a duration of the pre-heating phase lies within a range of seconds,

to generate control signals which are convertible into gate activation signals for gates of the power semiconductors and which define a pre-heating current impressed into the electric machine during the pre-heating phase in response to execution of the gate activation signals, and

to output the control signals via the signal output.

17. A computer program configured for operating the computing unit of claim 16 .

18. An activation apparatus, comprising:

a signal input configured for receiving the control signals generated by the computing unit of claim 16 ; and

gate activation signal outputs, said activation apparatus being configured

to generate the gate activation signals for the power semiconductor as a function of the control signals, and

to output the gate activation signals to the gates of the power semiconductor via the gate activation signal outputs.

19. A computer program product, on which the computer program of claim 17 is stored.

20. A converter, comprising:

power semiconductors arranged in the converter;

a temperature sensor for measuring a temperature of the power semiconductors;

a computing unit, said computing unit comprising a temperature input for receiving the temperature of at least one of the power semiconductors measured with the temperature sensor, and a signal output, said computing unit being configured to perform a comparison of the measured temperature with a reference temperature and to provide a result of the comparison, to activate a pre-heating phase for preheating the power semiconductors as a function of the result, said pre-heating phase being activated resulting in an increase in I HEAT when the result indicates that the temperature of the at least one power semiconductor is lower than the reference temperature and a collector current I C is dropped to a value approximating zero, and wherein the pre-heating phase is not activated when the result indicates that the temperature of the at least one power semiconductor is greater than or equal to the reference temperature, wherein a duration of the pre-heating phase lies within a range of seconds, to generate control signals which are convertible into gate activation signals for gates of the power semiconductors and which define a pre-heating current impressed into the electric machine during the pre-heating phase in response to execution of the gate activation signals, and to output the control signals via the signal output;

a computer program product and a computer program stored on the computer program product, said computer program being configured for operating the computing unit,

an activation apparatus, comprising a signal input configured for receiving the control signals of the computing unit, and gate activation signal outputs, said activation apparatus being configured to form the gate activation signals for the power semiconductor, and to output the gate activation signals to the gates of the power semiconductor via the gate activation signal outputs.

21. The converter of claim 20 , further comprising an intermediate DC circuit.

22. An electric or hybrid vehicle, comprising the converter of claim 20 , and an electric machine operable by the converter.

23. The electric or hybrid vehicle of claim 22 , wherein the electric machine is constructed as an asynchronous machine or a synchronous machine.