Voltage source converter selectively delaying dead time

1 . A switching valve of a limb portion of a voltage source converter, the switching valve comprising a plurality of modules, each module including at least one switching element and at least one energy storage device, the or each switching element and the or each energy storage device in each module arranged to be combinable to selectively provide a voltage source, the switching valve including a controller programmed to selectively control the switching of the switching elements to select zero, one or more of the modules to contribute a or a respective voltage to a switching valve voltage;

wherein the controller is programmed to selectively control the switching of the switching elements to carry out a switching operation, the switching operation including switching at least one of the modules into circuit in the switching valve and/or switching at least one of the modules out of circuit from the switching valve; and

wherein the controller is programmed to apply a time delay to a start time of the switching operation to switch the at least one module into circuit in the switching valve based on a direction of current in the switching valve indicating that a charging current is flowing through each of the modules and/or apply the time delay to a start time of the switching operation to switch the at least one module out of circuit from the switching valve based on the direction of the current in the switching valve indicating that a discharging current is flowing through each of the modules, wherein the time delay includes a sum of a dead-time and a switching element turn-on time reduced by a switching element turn-off time, and wherein the time delay is further increased by a reverse recovery time of the switching element.

2 . A switching valve according to claim 1 , wherein the controller is programmed to selectively control the switching of the switching elements to simultaneously carry out first and second switching operations, the first switching operation including switching at least one first module of the modules into circuit in the switching valve, the second switching operation including switching at least one second module of the modules out of circuit from the switching valve,

wherein the controller is programmed to apply the time delay to a first start time of the first switching operation if a charging current is flowing through the modules and/or apply a second time delay to a second start time of the second switching operation if a discharging current is flowing through the modules.

3 . A switching valve according to claim 1 , wherein the switching element turn-on time is a function of a switching element turn-on delay time and a switching element turn-on rise time.

4 . A switching valve according to claim 1 , wherein the switching element turn-off time is a function of a switching element turn-off delay time and a switching element turn-off fall time.

5 . A switching valve according to claim 1 , wherein each switching element includes a switching device connected in anti-parallel with a passive current check element.

6 . A switching valve according to claim 1 , wherein the time delay includes a sum of a module dead-time, a switching element turn-on time and reverse recovery time reduced by a switching element turn-off time.

7 . A voltage source converter comprising at least one switching valve according to claim 1 .

8 . A switching valve according to claim 1 , wherein each module further includes a protection circuit comprising a mechanical switch and a thyristor connected in parallel to each other and to the voltage source.

9 . A switching valve according to claim 1 , wherein the voltage source is a bidirectional voltage source.

10 . A switching valve according to claim 9 , wherein the bidirectional voltage source comprises a 4-quadrant bipolar module configurable to provide a positive voltage, a negative voltage, or zero voltage and support bidirectional current conduction.

11 . A method of operating a switching valve of a limb portion of a voltage source converter, the switching valve comprising a plurality of modules, each module including at least one switching element and at least one energy storage device, the or each switching element and the or each energy storage device in each module arranged to be combinable to selectively valve, wherein the at least one of the modules switched into circuit is a different number of modules than the at least one of the modules switched out of circuit; and provide a voltage source, the method comprising the steps of:

controlling the switching of the switching elements to select zero, one or more of the modules to contribute a or a respective voltage to a switching valve voltage;

controlling the switching of the switching elements to carry out a switching operation, the switching operation including switching at least one of the modules into circuit in the switching valve and/or switching at least one of the modules out of circuit from the switching valve; and

applying a time delay to a start time of the switching operation to switch the at least one module into circuit in the switching valve based on a direction of current in the switching valve indicating that a charging current is flowing through each of the modules and/or applying the time delay to a start time of the switching operation to switch the at least one module out of circuit from the switching valve based on the direction of the current in the switching valve indicating that a discharging current is flowing through each of the modules, wherein the time delay includes a sum of a dead-time and a switching element turn-on time reduced by a switching element turn-off time, and wherein the time delay is further increased by a reverse recovery time of the switching element.

12 . A method according to claim 11 , including the steps of:

controlling the switching of the switching elements to simultaneously carry out first and second switching operations, the first switching operation including switching at least one first module of the modules into circuit in the switching valve, the second switching operation including switching at least one second module of the modules out of circuit from the switching valve,

applying the time delay to a first start time of the first switching operation if a charging current is flowing through the modules and/or applying the time delay to a second start time of the second switching operation if a discharging current is flowing through the modules, wherein the time delay includes a sum of a module dead-time and a switching element turn-on time reduced by a switching element turn-off time.

13 . A method according to claim 11 , wherein the switching element turn-on time is a function of a switching element turn-on delay time and a switching element turn-on rise time.

14 . A method according to claim 11 , wherein the switching element turn-off time is a function of a switching element turn-off delay time and a switching element turn-off fall time.

15 . A method according to claim 11 , wherein each switching element includes a switching device connected in anti-parallel with a passive current check element.

16 . A method according to claim 15 , wherein the time delay includes a sum of a module dead-time, a switching element turn-on time and reverse recovery time reduced by a switching element turn-off time.

17 . A method of operating a voltage source converter, the voltage source converter comprising at least one switching valve, the or each switching valve comprising a plurality of modules, each module including at least one switching element and at least one energy storage device, the or each switching element and the or each energy storage device in each module arranged to be combinable to selectively provide a voltage source, the method comprising the method of claim 11 .

18 . A method according to claim 11 , wherein the voltage source is a bidirectional voltage source.