A voltage source converter includes DC terminals, a plurality of single-phase limbs, and a controller. Each single-phase limb includes a phase element and switching elements. Each limb is connected between the DC terminals and is controllable to generate an AC voltage at the AC side of the corresponding phase element so as to draw a respective phase current from a multi-phase AC electrical network. The controller is configured to selectively generate a modified AC voltage demand for at least one limb in response to an imbalance in the phase currents and/or a change in electrical rating of at least one limb. The controller is configured to selectively control, in accordance with the or the respective modified AC voltage demand, the or each corresponding limb independently of the or each other limb to modify the voltage at the AC side of its phase element and thereby modify the corresponding phase current.