Converter cell and associated converter arm and method for preventing undesired overcharging of energy storage device of the converter cell
View Patent ↗It is presented a converter cell comprising: a first terminal and a second terminal; an energy storage device connected on a first end to the second terminal; a first switch connected on a first end to the first terminal; a second switch arranged between the two terminals; and a third switch connected between a second end of the first switch and a second end of the energy storage device. A corresponding converter arm and method are also presented.
1. A converter arm comprising a plurality of converter cells, each converter cell comprising:
a first terminal and a second terminal;
an energy storage device connected on a first end to the second terminal;
a first switch connected on a first end to the first terminal;
a second switch arranged between the two terminals; and
a third switch connected between a second end of the first switch and a second end of the energy storage device,
wherein the converter cell is arranged to open the first switch and the third switch when the second switch has failed into an open circuit.
2. The converter arm according to claim 1 , wherein the converter cell is arranged to open the third switch when the first switch has failed.
3. The converter arm according to claim 2 , wherein the converter cell is arranged to open the third switch when the first switch has failed into an open circuit or a short circuit.
4. The converter arm according to claim 3 , wherein the third switch comprises two antiparallel thyristors.
5. The converter arm according to claim 3 , wherein the third switch comprises a bidirectional thyristor.
6. The converter arm according to claim 2 , wherein the converter cell is arranged to open the third switch to prevent charging of the energy storage device.
7. The converter arm according to claim 6 , wherein the third switch comprises two antiparallel thyristors.
8. The converter arm according to claim 2 , wherein the third switch comprises two antiparallel thyristors.
9. The converter arm according to claim 2 , wherein the third switch comprises a bidirectional thyristor.
10. The converter arm according to claim 1 , wherein the third switch comprises two antiparallel thyristors.
11. The converter arm according to claim 10 , wherein the converter cell is arranged to control energisation of the energy storage device by controlling a phase angle of one of the thyristors allowing a current to energise the energy storage device.
12. The converter arm according to claim 1 , wherein the third switch comprises a bidirectional thyristor.
13. The converter arm according to claim 1 , wherein the third switch comprises a thyristor in parallel with a mechanical switch.
14. The converter arm according to claim 1 , wherein each of the first and second switches comprises a semiconductor device and an antiparallel diode.
15. The converter arm according to claim 14 , wherein the semiconductor device is an insulated gate bipolar transistor, IGBT.
16. The converter arm according to claim 1 , wherein the energy storage device is a capacitor.
17. A method for controlling a converter arm comprising a plurality of converter cells, each converter cell comprising a first terminal and a second terminal; an energy storage device connected on a first end to the second terminal; a first switch connected on a first end to the first terminal; a second switch arranged between the two terminals; and a third switch connected between a second end of the first switch and a second end of the energy storage device, the method comprising the step of:
when the second switch has failed into an open circuit, opening the first switch the third switch.
18. The method for controlling the converter arm according to claim 17 , further comprising the step of: when the first switch fails, opening the third switch.
19. The method for controlling the converter arm according to claim 18 , further comprising the step of:
controlling the third switch to limit power transfer to the energy storage device.