Switching branch for three-level rectifier and method for controlling switching branch for three-level rectifier

1. A switching branch for a three-level rectifier, the switching branch comprising:

a first diode and a second diode connected in series between an AC input pole of the switching branch and a positive DC output pole;

a third diode and a fourth diode connected in series between the AC input pole of the switching branch and a negative DC output pole;

a first controllable switch connected between a neutral DC output pole and a first connection point between the first diode and the second diode;

a second controllable switch connected between the neutral DC output pole and a second connection point between the third diode and the fourth diode;

means for controlling the first controllable switch to be in a conductive state during a reverse blocking state of the first diode and the second diode; and

means for controlling the second controllable switch to be in a conductive state during a reverse blocking state of the third diode and the fourth diode.

2. The switching branch of claim 1 , wherein

the means for controlling the first switch are configured to control the first switch to be in the conductive state for each entire period of the reverse blocking state of the first diode and the second diode; and

the means for controlling the second switch are configured to control the second switch to be in the conductive state for each entire period of the reverse blocking state of the third diode and the fourth diode.

3. The switching branch of claim 1 , comprising:

a fifth diode connected in parallel with the first switch; and

a sixth diode connected in parallel with the second switch.

4. The switching branch of claim 1 , wherein the controllable switches are semiconductor switches.

5. A three-phase three-level rectifier comprising three switching branches according to claim 1 .

6. A method for controlling a switching branch for a three-level rectifier,

wherein the switching branch includes a first diode and a second diode connected in series between an AC input pole of the switching branch and a positive DC output pole, a third diode and a fourth diode connected in series between the AC input pole of the switching branch and a negative DC output pole, a first controllable switch connected between a neutral DC output pole and a first connection point between the first and the second diode, and a second controllable switch connected between the neutral DC output pole and a second connection point between the third and the fourth diode, wherein the method comprises:

controlling the first controllable switch to be in a conductive state during a reverse blocking state of the first diode and the second diode; and

controlling the second controllable switch to be in a conductive state during a reverse blocking state of the third diode and the fourth diode.

7. The method of claim 6 , wherein:

the controlling of the first switch comprises controlling the first switch to be in the conductive state for each entire period of the reverse blocking state of the first diode and the second diode; and

the controlling of the second switch comprises controlling the second switch to be in the conductive state for each entire period of the reverse blocking state of the third diode and the fourth diode.

8. The method of claim 6 , wherein the switching branch includes a fifth diode connected in parallel with the first switch, and a sixth diode connected in parallel with the second switch.

9. The method of claim 6 , wherein the controllable switches are semiconductor switches.

10. A non-transitory computer-readable recording medium having a computer program recorded thereon that causes a processor of a computing device to carry out operations for controlling a switching branch for a three-level rectifier,

wherein the switching branch includes a first diode and a second diode connected in series between an AC input pole of the switching branch and a positive DC output pole, a third diode and a fourth diode connected in series between the AC input pole of the switching branch and a negative DC output pole, a first controllable switch connected between a neutral DC output pole and a first connection point between the first and the second diode, and a second controllable switch connected between the neutral DC output pole and a second connection point between the third and the fourth diode, and

wherein the program causes the processor to carry out operations comprising:

controlling the first controllable switch to be in a conductive state during a reverse blocking state of the first diode and the second diode; and

controlling the second controllable switch to be in a conductive state during a reverse blocking state of the third diode and the fourth diode.

11. The non-transitory computer-readable recording medium of claim 10 , wherein:

the controlling of the first switch comprises controlling the first switch to be in the conductive state for each entire period of the reverse blocking state of the first diode and the second diode; and

the controlling of the second switch comprises controlling the second switch to be in the conductive state for each entire period of the reverse blocking state of the third diode and the fourth diode.

12. The non-transitory computer-readable recording medium of claim 10 , wherein the switching branch includes a fifth diode connected in parallel with the first switch, and a sixth diode connected in parallel with the second switch.

13. The non-transitory computer-readable recording medium of claim 10 , wherein the controllable switches are semiconductor switches.

14. A switching branch for a three-level rectifier, the switching branch comprising:

a first diode and a second diode connected in series between an AC input pole of the switching branch and a positive DC output pole;

a third diode and a fourth diode connected in series between the AC input pole of the switching branch and a negative DC output pole;

a first controllable switch connected between a neutral DC output pole and a first connection point between the first diode and the second diode;

a second controllable switch connected between the neutral DC output pole and a second connection point between the third diode and the fourth diode; and

a control arrangement configured to control the first controllable switch to be in a conductive state during a reverse blocking state of the first diode and the second diode, and to control the second controllable switch to be in a conductive state during a reverse blocking state of the third diode and the fourth diode.

15. The switching branch of claim 14 , wherein the control arrangement is configured to control the first switch to be in the conductive state for each entire period of the reverse blocking state of the first diode and the second diode, and to control the second switch to be in the conductive state for each entire period of the reverse blocking state of the third diode and the fourth diode.

16. The switching branch of claim 14 , wherein the switching branch comprises:

a fifth diode connected in parallel with the first switch; and

a sixth diode connected in parallel with the second switch.

17. The switching branch of claim 14 , wherein the controllable switches are semiconductor switches.

18. A three-phase three-level rectifier comprising three switching branches according to claim 14 .