Abstract: 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 which comprises a plurality of converter limbs connected in series between first and second DC terminals that are connectable in use to a DC network. Each converter limb includes first and second series connection points between which extends a longitudinal chain-link converter that is operable to provide a stepped variable voltage. Each first series connection point is electrically connected with a corresponding first AC connection terminal via a first transverse branch. Each second series connection point is electrically connected with a corresponding second AC connection terminal via a second transverse branch. The first and second AC connection terminals together define an AC connection that is connectable in use to a respective phase of an AC network.

Abstract: An alternate arm converter includes at least one converter limb that defines first and second limb portions. Each limb portion includes at least one director switch connected in series with a chain-link converter between one of two DC terminals and an AC terminal of the converter. The chain-link converters are operable to generate a voltage waveform at the AC terminal, and the director switches are operable to switch the respective chain-link converters in and out of circuit between the respective DC terminal and the AC terminal. The converter also includes a controller configured to selectively control the switching of each director switch to form a current circulation path including each limb portion and the DC network. The controller, during formation of the current circulation path, forces an alternating current to flow through the current circulation path to transfer energy between the chain-link converters of the limb portions.

Abstract: An alternate arm converter includes at least one converter limb that defines first and second limb portions. Each limb portion includes at least one director switch connected in series with a chain-link converter between one of two DC terminals and an AC terminal of the converter. The chain-link converters are operable to generate a voltage waveform at the AC terminal, and the director switches are operable to switch the respective chain-link converters in and out of circuit between the respective DC terminal and the AC terminal. The converter also includes a controller configured to selectively control the switching of each director switch to form a current circulation path including each limb portion and the DC network. The controller, during formation of the current circulation path, forces an alternating current to flow through the current circulation path to transfer energy between the chain-link converters of the limb portions.