Patent ID: 8704498

Claim:
A voltage source converter ( 10 ) for use in three-phase high voltage DC power transmission and reactive power compensation, the voltage source converter comprising three converter limbs ( 12 , 14 , 16 ) connected in a bridge circuit arrangement wherein each of first ( 12 ) and second ( 14 ) converter limbs includes a multilevel converter ( 18 ) and a third converter limb ( 16 ) includes a capacitor ( 20 ) on each side of a series AC phase connection ( 22 ), the multilevel converters ( 18 ) being a chain-link converter controllable to synthesize waveforms at series AC phase connections ( 24 , 26 ) of the first and second converter limbs, with each chain-link converter including a chain of modules ( 34 ) connected in series and each module includes at least one pair of semiconductor switches ( 36 ) connected in parallel with an energy storage device ( 38 ), the semiconductor switches being controllable in use to provide a continuously variable voltage source, characterized in that each chain-link converter further includes a combination of: modules in which the semiconductor switches ( 36 ) of the module are connected with the respective energy storage device in a half-bridge arrangement to define a 2-quadrant unipolar module that can develop zero or positive voltage and can conduct current in both direction, and modules ( 34 ) in which the semiconductor switches of the module are connected with the respective energy storage device in a full-bridge arrangement to define a 4-quadrant bipolar module that can develop positive or negative voltage and can conduct current in both directions.