Abstract: In the field of high voltage direct current (HVDC) power transmission networks, there is a need for improvements to allow a single power converter to control individual AC network voltages carried by multiple AC transmission conduits to multiple AC network elements, such as respective wind parks.

Abstract: An electrical assembly includes a converter-based electrical device and a transformer for connecting the converter-based electrical device to an AC electrical network, a first transformer side of the transformer connected to the converter-based electrical device, a second transformer side of the transformer for connection to the AC electrical network, the transformer including a number of taps, the transformer including a tap changer operable to selectively connect to the or each tap to modify a turn ratio of the transformer. The transformer includes a controller configured to selectively operate the tap changer in an AC voltage modification mode, responsive to an abnormal operating state of the electrical assembly, to modify the turn ratio of the transformer so as to modify an AC voltage at the first transformer side.

Abstract: A voltage source converter having first and second DC terminals for connection to a DC network is provided. The voltage source converter includes at least one converter limb that extends between the first and second DC terminals and first and second limb portions that are separated by a respective AC terminal for connection to a corresponding phase of an AC network. Each limb portion includes a chain-link converter which is defined by a plurality of series-connected switching modules which operate in combination to provide a stepped variable voltage source. The voltage source converter includes a control apparatus configured to coordinate operation of the chain-link converters to cause an exchange of power between the DC and AC networks, evaluate the performance of one of the pluralities of series-connected switching modules, and modify the operation of the respective chain-link converter when the performance becomes degraded to a predetermined amount.

Abstract: There is provided a switching valve for a voltage source converter.

Abstract: In the field of chain-link converters operable to provide a stepped variable voltage source, there is a need for an improved method of operating such a chain-link converter. A method of operating a chain-link converter, the chain-link converter including a number of series connected chain-link modules, each chain-link module including at least one switching element and an energy storage device which together are selectively operable to provide a voltage source whereby the chain-link converter is able to provide a stepped variable voltage source, including the steps of: (i) identifying one or more unhealthy chain-link modules having a reduced performance characteristic compared to one or more healthy chain-link modules having a normal performance characteristic, (ii) utilizing the healthy chain-link modules normally in the operation of the chain-link converter, and (iii) reducing the utilization of the or each unhealthy chain-link module.

Abstract: There is provided a switching valve for a voltage source converter.

Abstract: In the field of high voltage direct current (HVDC) power transmission networks, there is a need for improvements to allow a single power converter to control individual AC network voltages carried by multiple AC transmission conduits to multiple AC network elements, such as respective wind parks. A power transmission network (10; 100) comprises a power converter (12) which has first and second DC converter terminals (14, 16) that are for connection, in use, to a DC network. The power converter (12) also includes an AC converter terminal (22) which is electrically connected to a plurality of AC transmission conduits (241, 242, 24n), each of which is for connection, in use, to a respective AC network element (261, 262, 26n) that is configured to operate at a respective individual AC network voltage.

Abstract: In the field of high voltage direct current (HVDC) transmission, a voltage source converter comprises first and second DC terminals that are for connection to a DC network. The voltage source converter also includes at least one converter limb. The or each converter limb extends between the first and second DC terminals and includes first and second limb portions that are separated by a respective AC terminal for connection to a corresponding phase of an AC network. Each first limb portion extends between the first DC terminal and a corresponding AC terminal, and each second limb portion extends between the second DC terminal and the corresponding AC terminal. Each limb portion includes a respective chain-link converter which is defined by a plurality of series-connected switching modules which are operable in combination to provide a stepped variable voltage source.

Abstract: A method of controlling current in a three-phase voltage converter operating in current imbalance mode, the method being: determining a setpoint limit value for forward current (Idlim*) as a function of a current capacity of the converter (Ilim) and of forward balanced current (Id*); determining a maximum reverse current value (Iimax) as a function of the determined forward current setpoint limit value (Idlim*) and such that the phase currents are at a maximum; and determining a reverse current setpoint limit value (Iilim*) as a function of the maximum value of the reverse current (Iimax) and of a reverse balanced current (Ii*).