Voltage source converter switching valve with dynamic target voltage

A switching valve for 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 regulator programmed to selectively control the switching of the switching elements to select one or more of the modules to contribute a respective voltage to a switching valve voltage,
• wherein the regulator is programmed to selectively regulate an energy stored in each energy storage device by controlling the switching of the switching elements to regulate a voltage of each energy storage device to or towards a target voltage, and the regulator is programmed to vary the target voltage of each energy storage device as a function of a number of healthy modules in the switching valve,
• wherein the regulator is programmed to determine the target voltage of each energy storage device as a function of a voltage factor of the voltage source converter when varying the target voltage of each energy storage device as a function of a number of healthy modules in the switching valve so that the energy stored in each energy storage device stays above a lower energy storage limit of that energy storage device,
• wherein the voltage factor is a function of a measured direct current (DC) voltage of the voltage source converter, and
• wherein the regulator is further programmed to:
• compare the voltage factor to a voltage factor reference threshold;
• and
• apply a voltage offset to the target voltage based on the comparison.