Voltage source converter

A voltage source converter comprising:

• at least one DC terminal for connection to a DC electrical network;
• a converter limb operatively connected to the at least one DC terminal, the converter limb including at least one limb portion operatively connected to an AC terminal, the AC terminal being connectable to an AC electrical network, the or each limb portion including a valve, the or each valve including at least one module, the or 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 the or each module combining to selectively provide a voltage source;
• a controller including a valve voltage demand sub-controller, the controller being configured to provide a zero alternating current demand, for an alternating current flowing between the voltage source converter and the AC electrical network, and a direct current demand, for a direct current flowing between the voltage source converter and the DC electrical network, to the valve voltage demand sub-controller, the controller being further configured to provide AC and DC output voltage demands to the valve voltage demand sub-controller, the valve voltage demand sub-controller being configured to process the alternating and direct current demands and the AC and DC output voltage demands so as to generate a or a respective valve voltage demand for the or each valve;
• and
• a switching control unit configured to control switching of the or each switching element in the or each module so as to generate a voltage across the or each valve in accordance with the or the respective valve voltage demand and thereby cause transfer of power between the AC and DC electrical networks.