Redundant current valve control in a high voltage power transmission system

1. A method for providing redundant control of at least one controllable current valve provided in a converter of a high voltage power transmission system, the method comprising:

sending a first valve control signal for said at least one controllable valve and an associated first active/standby indicator from a first converter control unit to a first valve control element of a valve control unit,

sending a second valve control signal for said at least one controllable valve and an associated second active/standby indicator from a second control element of said valve control unit, wherein an active/standby indicator indicates if a corresponding converter control unit is an active or standby converter control unit and only one active/standby indicator indicates an active converter control unit at a given point in time, such that two active/standby indicators cannot simultaneously indicate an active converter control unit,

receiving, with said valve control unit, said active/standby indicators and said first and second valve control signals,

selecting, with said valve control unit, a valve control signal to be used for controlling said current valve if the associated active/standby indicator indicates an active converter control unit, wherein the selecting comprises

determining by the first valve control element if said first valve control signal is to be applied based on the first active/standby indicator, and

determining by the second valve control element if said second valve control signal is to be applied based on the second active/standby indicator,

wherein the determinations are performed in parallel independently of each other and

controlling said current valve using said selected valve control signal.

2. The method according to claim 1 , wherein the controlling comprises converting the valve control signal that is associated with an active/standby indicator indicating an active converter control unit to a valve driving signal, and applying said valve driving signal to said valve.

3. The method according to claim 1 , further comprising:

returning, with the valve control unit, an acknowledgement of each received converter control signal to the corresponding converter control unit through returning said received valve control signal.

4. The method according to claim 1 , further comprising:

supervising, with each converter control unit, a functionality and a handing over of each converter control unit, with the active converter control unit, control to the standby converter control unit in case faults are detected in the supervised functionality.

5. The method according to claim 4 , wherein the handing over control is performed using handshaking.

6. The method according to claim 1 , further comprising:

monitoring, with a system protection unit, at least one operating condition of the system, providing, by said system protection unit, a system safety measure in case the operating condition reaches a risk state and ordering, with the system protection unit, the active converter control unit to handover control to the standby converter control unit if the monitored operating condition is in proximity of the risk state.

7. The method according to claim 1 , wherein the high voltage power transmission system is a DC power transmission system.

8. The method according to claim 1 , wherein the high voltage power transmission system is operating at voltages around 800 kV.

9. A device for providing redundant control of at least one controllable current valve provided in a converter of a high voltage power transmission system, the device comprising:

a first converter control unit arranged to send a first valve control signal for said at least one controllable valve and an associated first active/standby indicator,

a second converter control unit arranged to send a second valve control signal for said at least one controllable valve and an associated second active/standby indicator, wherein an active/standby indicator indicates if a corresponding converter control unit is an active or standby converter control unit and only one active/standby indicator indicates an active converter control unit at a given point in time, such that two active/standby indicators cannot simultaneously indicate an active converter control unit, and

a valve control unit comprising

a first valve control element arranged to receive said first valve control signal from said first converter control unit, receive said first active/standby indicator and to determine if said first valve control signal is to be applied based on the first active/standby indicator, and

a second valve control element arranged to receive said second valve control signal, receive said second active/standby indicator and to determine if said second valve control signal is to be applied based on the second active/standby indicator,

wherein the first and second valve control elements are arranged to perform said determinations in parallel independently of each other,

wherein the valve control unit is arranged to

receive said active/standby indicators and said first and second valve control signals,

select a valve control signal to be applied for controlling said current valve if the corresponding active/standby indicator indicates an active converter control unit, and

control said current valve using said selected valve control signal.

10. The device according to claim 9 , wherein the valve control element which has received an active/standby indicator indicating an active converter control unit is further arranged to convert the corresponding valve control signal to a valve driving signal to be applied to said at least one controllable valve.

11. The device according to claim 9 , wherein each valve control element is arranged to return an acknowledgement to the corresponding converter control unit through returning said received valve control signal.

12. The device according to claim 9 , wherein each converter control unit is arranged to supervise its own functionality and the active converter control unit is further arranged to handover control to the standby converter control unit in case faults are detected in the supervised functionality.

13. The device according to claim 12 , wherein the active converter control unit is arranged to handover control to the standby converter control unit through handshaking.

14. The device according to claim 9 , further comprising:

a system protection unit arranged to monitor at least one operating condition of the system and to provide a system safety measure in case the operating condition reaches a risk state, wherein the system protection unit is further arranged to order the active converter control unit to handover control to the standby converter control unit if the monitored operating condition is in proximity of the risk state.