Electrical converter and control method

1. A method for controlling an electrical multi-phase converter, the electrical multi-phase converter comprising at least two phase branches for providing at least two output voltages, wherein each phase branch comprises at least one converter cell supplied with a supply voltage (US_mn) , and the at least two phase branches are adapted for converting the supply voltages (US_mn) into the at least two output voltages, the method comprising:

determining at least two supply voltages (US_mn) for the at least two converter cells of the at least two phase branches;

determining a potential zone for each phase branch based on the at least one supply voltage (US_mn) of the at least one converter cell of the phase branch, the potential zone bounding a possible actual phase voltage producible by the phase branch;

receiving a reference voltage (Ur_m) for each phase branch;

if the reference voltage (Ur_m) for a phase branch is not within the potential zone of the phase branch, setting the reference voltage (U_(r_m)^′) to a bound of the potential zone and shifting reference voltages of other phase branches) by:

determining an excess voltage (Ur_p_ex) for the phase branch, the excess voltage being based on a difference between the reference voltage (Ur_p) and a violated bound of the potential zone;

modifying the reference voltage (U_(r_m)^′) for each phase branch by subtracting the excess voltage (Ur_p_ex) from the reference voltage (Ur_m) of the phase branch, such that a minimal common mode voltage between the output voltages of the multi-phase converter is generated.

2. The method of claim 1 ,

wherein, for each phase branch, a maximal available voltage (US_m) at the phase branch is determined from the at least one supply voltage (US_mn) provided by the at least one converter cell of the phase branch;

wherein the potential zone is bounded by the maximal available voltage (US_m) and the negated maximal available voltage.

3. The method of claim 2 ,

wherein the electrical multi-phase converter comprises one converter cell per phase branch and the maximal available voltage (US_m) for a phase branch is the absolute value of the supply voltage (US_mn) of the one converter cell of the phase branch; or

wherein the electrical multi-phase converter comprises more than one converter cell per phase branch and the maximal available voltage (US_m) for a phase branch ( 22 ) is the sum of the absolute values of the supply voltages (US_mn) of the converter cells of the phase branch.

4. The method of claim 2 ,

wherein the excess voltage (Ur_p_ex) is the difference between the reference voltage (Ur_p) and a violated bound based on the maximal available voltage (US_m).

5. The method of claim 2 ,

wherein it is determined, whether the reference voltage (Ur_m) for a phase branch is within the potential zone of the phase branch or not, by comparing, whether the reference voltage (Ur_m) is smaller than a lower bound of the potential zone and/or greater than an upper bound of the potential zone.

6. The method of claim 2 ,

wherein the supply voltage (US_mn) for each converter cell is measured.

7. The method of claim 2 ,

wherein the supply voltage (US_mn) is a DC link voltage.

8. The method of claim 2 , further comprising:

determining switching states of the converter cells based on the modified reference voltages (U_(r_m)^′), such that output voltages of the phase branches ( 22 ) reproduce the modified reference voltages (U_(r_m)^′).

9. A controller for controlling an electrical multi-phase converter, the electrical multi-phase converter comprising at least two phase branches for providing at least two output voltages, wherein each phase branch comprises at least one converter cell supplied with a supply voltage, and the at least two phase branches are adapted for converting the supply voltages into the at least two output voltages, wherein the controller is adapted to:

determine at least two supply voltages for the at least two converter cells of the at least two phase branches;

determine a potential zone for each phase branch based on the at least one supply voltage of the at least one converter cell of the phase branch, the potential zone bounding a possible actual phase voltage producible by the phase branch;

receive a reference voltage for each phase branch;

if the reference voltage for a phase branch is not within the potential zone of the phase branch, the controller is further adapted to set the reference voltage to a bound of the potential zone and shift reference voltages of other phase branches by:

determining an excess voltage for the phase branch, the excess voltage being based on a difference between the reference voltage and a violated bound of the potential zone;

modifying the reference voltage for each phase branch by subtracting the excess voltage from the reference voltage of the phase branch, such that a minimal common mode voltage between the output voltages of the multi-phase converter is generated.

10. An electrical multi-phase converter, comprising:

at least two phase branches for providing an output voltage;

at least two converter cells for converting at least two supply voltages into at least two output voltages; and

a controller for controlling the converter cells and adapted to:

determine at least two supply voltages for the at least two converter cells of the at least two phase branches;

determine a potential zone for each phase branch based on the at least one supply voltage of the at least one converter cell of the phase branch, the potential zone bounding a possible actual phase voltage producible by the phase branch;

receive a reference voltage for each phase branch;

if the reference voltage for a phase branch is not within the potential zone of the phase branch, the controller is further adapted to set the reference voltage to a bound of the potential zone and shift reference voltages of other phase branches by:

determining an excess voltage for the phase branch, the excess voltage being based on a difference between the reference voltage and a violated bound of the potential zone;

modifying the reference voltage for each phase branch by subtracting the excess voltage from the reference voltage of the phase branch, such that a minimal common mode voltage between the output voltages of the multi-phase converter is generated.

11. The electrical multi-phase converter of claim 10 , wherein the electrical converter comprises more than one converter cell per phase branch, and the converter cells of each phase branch are series-connected at their outputs.

12. The electrical multi-phase converter of claim 10 ,

wherein each converter cell comprises an H-bridge inverter.

13. The electrical multi-phase converter of claim 10 ,

wherein each converter cell comprises a rectifier and an inverter, which are interconnected by a DC link, which provides a DC supply voltage for the inverter.

14. The electrical multi-phase converter of claim 10 ,

wherein the phase branches are star-connected.

15. The method claim 3 ,

wherein the excess voltage is the difference between the reference voltage and a violated bound based on the maximal available voltage.

16. The method of claim 3 ,

wherein it is determined, whether the reference voltage for a phase branch is within the potential zone of the phase branch or not, by comparing, whether the reference voltage is smaller than a lower bound of the potential zone and/or greater than an upper bound of the potential zone.

17. The method of claim 3 ,

wherein the supply voltage for each converter cell is measured.

18. The method of claim 3 ,

wherein the supply voltage is a DC link voltage.

19. The method of claim 3 , further comprising:

determining switching states of the converter cells based on the modified reference voltages, such that output voltages of the phase branches reproduce the modified reference voltages.

20. The electrical multi-phase converter of claim 11 ,

wherein each converter cell comprises an H-bridge inverter.