Method and system for determining a phase shift between a phase current and a phase voltage

1. A method for determining a phase shift between a phase current and a phase voltage in an AC phase line of a converter that carries a corresponding phase of an AC output of the converter, wherein a phase current change dependent quantity for the AC phase line is determined, wherein a voltage-specific reference time point for the AC phase line is determined depending on the phase current change dependent quantity, wherein the phase current for the AC phase line is determined, wherein a current-specific reference time point for the AC phase line is determined depending on the phase current, wherein the phase shift is determined depending on the time difference between the voltage-specific reference time point and the current-specific reference time point.

2. The method of claim 1 , characterized in that the voltage-specific reference time point is determined as the time point of a zero crossing of the phase current change dependent quantity.

3. The method of claim 1 , characterized in that a derivative of the phase current change dependent quantity is determined by differentiating the phase current change dependent quantity at least once, wherein the voltage-specific reference time point is determined as the time point of a zero crossing of the derivative.

4. The method of claim 1 , characterized in that the phase current is determined by integrating the phase current change dependent quantity over time.

5. The method of claim 1 , characterized in that the phase current change dependent quantity is determined by a Rogowski coil-based determining means.

6. The method of claim 1 , characterized in that the phase current change dependent quantity is compared to a first predetermined reference value by a first comparing means, wherein the phase current is compared to a further predetermined reference value by a further comparing means, wherein the voltage-specific reference time point is determined depending on an output signal of the first comparing means, wherein the current-specific reference time point is determined depending on an output signal of the further comparing means.

7. The method of claim 1 , characterized in that a trigger signal is generated, wherein the voltage-specific reference time point and the current-specific reference time point are determined as time points within a time interval of predetermined duration after the time point of generating the trigger signal.

8. The method of claim 7 , characterized in that the time point of generating the trigger signal is determined depending on a time point of a switch signal generation.

9. The method of claim 1 , wherein the converter is a converter of a system for inductive power transfer.

10. The method of claim 1 , wherein:

the converter is a three-phase converter comprising at least one leg having a series connection of first and second switching elements, the first switching element having first and second terminals, and the second switching element having first and second terminals;

the first terminal of the first switching element is electrically connected to a high potential DC line;

the second terminal of the first switching element is electrically connected to the first terminal of the second switching element to provide a connecting section;

the second terminal of the second switching element is electrically connected to a low potential DC line; and

the AC phase line is electrically connected to the connecting section.

11. The method of claim 1 , wherein the phase current change dependent quantity is a quantity that depends on a change in time of the phase current.

12. A system for determining a phase shift between a phase current and a phase voltage in an AC phase line of a converter that carries a corresponding phase of an AC output of the converter, wherein the system comprises at least one means for determining a phase current change dependent quantity for the AC phase line, at least one means for determining a voltage-specific reference time point for the AC phase line depending on the phase current change dependent quantity, at least one means for determining a phase current for the AC phase line, at least one means for determining a current-specific reference time point for the AC phase line depending on the phase current and at least one means for determining the phase shift depending on the time difference between the voltage-specific reference time point and the current-specific reference time point.

13. The system of claim 12 , characterized in that the means for determining a phase current change dependent quantity comprises a Rogowski coil-based determining means.

14. The system of claim 12 , wherein the converter is a converter of a system for inductive power transfer.

15. The system of claim 12 , wherein:

the converter is a three-phase converter comprising at least one leg having a series connection of first and second switching elements, the first switching element having first and second terminals, and the second switching element having first and second terminals;

the first terminal of the first switching element is electrically connected to a high potential DC line;

the second terminal of the first switching element is electrically connected to the first terminal of the second switching element to provide a connecting section;

the second terminal of the second switching element is electrically connected to a low potential DC line; and

the AC phase line is electrically connected to the connecting section.

16. The system of claim 12 , wherein the phase current change dependent quantity is a quantity that depends on a change in time of the phase current.