A VOLTAGE SOURCE CONVERTER

In the field of voltage source converters for use in high voltage direct current (HVDC) power transmission and reactive power compensation, there is provided a voltage source converter (10; 70; 80; 90; 110) which comprises a plurality of converter limbs (12 1 , 12 2 , 12 3 ) connected in series between first and second DC terminals (16, 18) that are connectable in use to a DC network (20). Each converter limb (12 1 , 12 2 , 12 3 ) includes first and second series connection points (22, 24) between which extends a longitudinal chain-link converter (26) that is operable to provide a stepped variable voltage (V 1 arm , V 2 arm , V 3 arm ). Each first series connection point (22) is electrically connected with a corresponding first AC connection terminal (42) via a first transverse branch (142). Each second series connection point (24) is electrically connected with a corresponding second AC connection terminal (46) via a second transverse branch (146). The first and second AC connection terminals (42, 46) together define an AC connection (48) that is connectable in use to a respective phase of an AC network (14). At least one transverse branch (142, 146) in each converter limb (12 1 , 12 2 , 12 3 ) includes a transverse circuit (44; 72; 82; 92) which has therein a transverse chain-link converter (56) that is operable to provide a stepped variable voltage (V 1 armT , V 2 armT , V 3 armT ).