Mechanical bypass switch device, converter arm and power converter

1. A mechanical bypass switch device arranged to be directly connected between the terminals of a first converter cell to bypass the first converter cell in a power converter, the mechanical switch device comprising:

a mechanical switch;

a mechanical switch actuator arranged to make the mechanical switch conduct when supplied with an electric signal;

a first control input;

a second control input;

a first control switch whose electrical conductive state is controlled using the first control input;

a second control switch whose electrical conductive state is controlled using the second control input; and

a control switch combination comprising the first control switch connected in parallel with the second control switch;

wherein the control switch combination is serially connected with the mechanical switch actuator, and

wherein the mechanical bypass switch device is arranged such that a control signal, provided on either one of the first control input and the second control input or on both of the first control input and the second control input, causes the mechanical switch to conduct and such that the first control input is to be connected with a local control unit of the first converter cell and the second control input is to be connected with a local control unit of a second converter cell.

2. The mechanical bypass switch device according to claim 1 , wherein the mechanical switch actuator comprises a pyrotechnic actuator.

3. The mechanical bypass switch device according to claim 1 , further comprising a monitoring device for detecting whether the mechanical switch is conducting.

4. A mechanical bypass switch device arranged to be directly connected between the terminals of a first converter cell to bypass the first converter cell in a power converter, the mechanical switch device comprising:

a mechanical switch;

a mechanical switch actuator arranged to make the mechanical switch conduct when supplied with an electric signal;

a first control input;

a second control input; and

a monitoring device for detecting whether the mechanical switch is conducting,

wherein the mechanical bypass switch device is arranged such that a control signal, provided on either one of the first control input and the second control input or on both of the first control input and the second control input, causes the mechanical switch to conduct and such that the first control input is to be connected with a local control unit of the first converter cell and the second control input is to be connected with a local control unit of a second converter cell, and

wherein the monitoring device comprises two signal outputs for supplying a signal indicating whether the mechanical switch is conducting to two separate devices.

5. A mechanical bypass switch device arranged to be directly connected between the terminals of a first converter cell to bypass the first converter cell in a power converter, the mechanical switch device comprising:

a mechanical switch;

a mechanical switch actuator arranged to make the mechanical switch conduct when supplied with an electric signal;

a first control input;

a second control input; and

a monitoring device for detecting whether the mechanical switch is conducting,

wherein the mechanical bypass switch device is arranged such that a control signal, provided on either one of the first control input and the second control input or on both of the first control input and the second control input, causes the mechanical switch to conduct and such that the first control input is to be connected with a local control unit of the first converter cell and the second control input is to be connected with a local control unit of a second converter cell, and

wherein the mechanical switch comprises a stationary part and a movable part, wherein the movable part either is attached to an optical fibre which is arranged to break when the movable part moves to make the mechanical switch conduct, or comprises a reflective surface which is arranged to reflect light when the movable part is in a position to make the mechanical switch conduct.

6. The mechanical bypass switch device according to claim 1 , wherein each one of the first control input and the second control input are fibre optic inputs.

7. The mechanical bypass switch device according to claim 1 , further comprising an energy storage device for powering the mechanical switch actuator.

8. The mechanical bypass switch device according to claim 1 , further comprising two energy storage devices.

9. The mechanical bypass switch device according to claim 7 , wherein any energy storage device is arranged to be charged from two separate power sources.

10. The mechanical bypass switch device according to claim 9 , wherein one power source is the converter cell and one power source is a local control unit, also being arranged to control the operation of the converter cell.

11. A converter arm comprising a plurality of serially connected converter cells, wherein each converter cell comprises an energy storage element, at least two switching elements and the mechanical bypass switch device according to claim 1 .

12. The converter arm according to claim 11 , wherein each converter cell is associated with a respective local control unit and wherein each local control unit is connected to one of the first control input and second control input of its associated converter cell and a converter cell neighbouring the associated converter cell.

13. The converter arm according to claim 12 , wherein the local control units are pairwise connected to their own and each other's respectively associated converter cell.

14. The converter arm according to claim 11 , wherein each one of the converter cells is a half bridge cell.

15. The converter arm according to claim 11 , wherein each one of the converter cells is a full bridge cell.

16. A power converter comprising at least one converter arm according to claim 12 .