Voltage source converter selectively delaying dead time

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.