A voltage source converter including a DC terminal for connection to a DC electrical network, and a converter limb operatively connected to the DC terminal. The converter limb including at least one limb portion operatively connected to an AC terminal. The limb portion including a valve, the valve including at least one module, the module including at least one switching element and at least one energy storage device, the switching element and each energy storage device in the module combining to selectively provide a voltage source. A controller including a valve voltage demand sub-controller. The controller being configured to provide AC and DC output voltage demands to the valve voltage demand sub-controller. And, a switching control unit configured to control switching of the switching element in the module so as to generate a voltage across the valve.