A voltage source converter includes three branches connected at a first end to a junction to form a star configuration, the second end of each branch defining a DC terminal, the second ends of the second and third branches being connectable to a first DC voltage, and the second ends of the first and second branches being connectable to a second DC voltage. The first and second branches include primary switching elements, and the third branch includes a primary inductive element. The converter includes a converter limb connected in parallel with one of the first and second branches, the converter limb including a chain-link auxiliary converter including multiple series-connected modules controllable to selectively provide a voltage source to modify a branch voltage across the branch connected in parallel with the converter limb, each module including at least one secondary switching element and at least one energy storage device.