Abstract: The present invention provides methods and apparatus for controlling HVDC power transmission systems so as to increase the effective lifetime of cables carrying the DC power (and particularly the extruded polymer insulation of those cables). The method includes entering a maintenance mode in which the electrical properties applied to the cable are varied so as to facilitate diffusion of space charge accumulation in the extruded polymer insulation.

Abstract: The present invention provides methods and apparatus for controlling HVDC power transmission systems so as to increase the effective lifetime of cables carrying the DC power (and particularly the extruded polymer insulation of those cables). The method includes entering a maintenance mode in which the electrical properties applied to the cable are varied so as to facilitate diffusion of space charge accumulation in the extruded polymer insulation.

Abstract: In the field of high voltage direct current power transmission networks, a method of controlling a converter that includes at least one converter limb which corresponds to a respective phase of the converter, is described. The method includes obtaining a respective AC current demand phase waveform for each converter limb which the corresponding converter limb is required to track, and a DC current demand which each converter limb is also required to track. The method further determining a limb portion current for each limb portion that the limb portion must contribute to track the corresponding required AC current demand phase waveform and the required DC current demand, and providing a limb portion voltage source for each limb portion to achieve the corresponding limb portion current. The method carrying out mathematical optimization to determine one or more optimal limb portion currents and/or provide optimal limb portion voltage sources.

Abstract: A voltage source converter of the controlled transition bridge type, having three phase limbs, each phase limb having a high &de director switch (Sw1 Sw3, Sw5) and a low side director switch (Sw4, Sw6, Sw2) connecting a respective DC terminal (DC+, DC?) to an AC node for that phase limb. Chain-link circuits for each phase limb comprise a plurality of series connect cells, each cell having an energy storage element that can be selectively connected in series or bypassed. The chain-link circuits are operated in a voltage mode to provide a defined voltage transition at the AC node during a transition between one director switch being turned off and the other director switch being turned on. Chain-link circuits are connected to a common node such that, in use, a current can flow from one phase limb to another via the respective chain-link circuits.

Abstract: A voltage source converter for interconnecting first and second electrical networks, including first and second terminals for connection to the first electrical network, and a primary converter limb extending between the first and second terminals including first and second primary limb portions separated by a third terminal connectable to the second electrical network. The converter further including a second chain-link converter connected to the third terminal and a control unit configured to selectively operate one or more chain-link modules to generate a discontinuous pulse width modulation voltage waveform. The converter further including a controller configured to selectively operate each chain-link converter to control the configuration of a discontinuous pulse width modulation voltage waveform at the third terminal.

Abstract: Embodiments relate to a voltage source converter of the controlled transition bridge type, having three phase limbs, each phase limb having a high side director switch (Sw1, SW3, SW5) and a low side director switch (Sw4, SW6, SW2) connecting a respective DC terminal (DC+, DC?) to an AC node for that phase limb. Chain-link circuits for each phase limb comprise a plurality of series connect cells, each cell having an energy storage element that can be selectively connected in series or bypassed. The chain-link circuits are operated in a voltage mode to provide a defined voltage transition at the AC node during a transition between one director switch being turned off and the other directors switch being turned on. In some embodiments, chain-link circuits are connected to a common node such that, in use, a current can flow from one phase limb to another via the respective chain-link circuits.

Abstract: A voltage source converter for interconnecting first and second electrical networks, including first and second terminals for connection to the first electrical network, and a primary converter limb extending between the first and second terminals including first and second primary limb portions separated by a third terminal connectable to the second electrical network. The converter further including a second chain-link converter connected to the third terminal and a control unit configured to selectively operate one or more chain-link modules to generate a discontinuous pulse width modulation voltage waveform. The converter further including a controller configured to selectively operate each chain-link converter to control the configuration of a discontinuous pulse width modulation voltage waveform at the third terminal.

Abstract: In the field of high voltage direct current (HVDC) power transmission, a converter comprises three converter limbs, each corresponding to a respective phase of the converter, each extending between first and second DC terminals and each including first and second limb portions separated by an AC terminal. Each limb portion that is operable to provide a stepped variable voltage source. The converter also includes a first controller that is programmed to selectively operate for one converter limb at a time the chain-link converter in each limb portion thereof to simultaneously adopt a current-conducting configuration and thereby define a fully-conducting converter limb to sequentially route via each said fully-conducting converter limb a DC current demand (IDC) between the first and second DC terminals.

Abstract: In the field of high voltage direct current power transmission networks, a method of controlling a converter that includes at least one converter limb which corresponds to a respective phase of the converter, is described. The method includes obtaining a respective AC current demand phase waveform for each converter limb which the corresponding converter limb is required to track, and a DC current demand which each converter limb is also required to track. The method further determining a limb portion current for each limb portion that the limb portion must contribute to track the corresponding required AC current demand phase waveform and the required DC current demand, and providing a limb portion voltage source for each limb portion to achieve the corresponding limb portion current. The method carrying out mathematical optimization to determine one or more optimal limb portion currents and/or provide optimal limb portion voltage sources.

Abstract: In the field of high voltage direct current (HVDC) power transmission, a converter comprises three converter limbs, each corresponding to a respective phase of the converter, each extending between first and second DC terminals and each including first and second limb portions separated by an AC terminal. Each limb portion includes a chain-link converter that is operable to provide a stepped variable voltage source, and a primary switching element to selectively switch the respective limb portion into and out of circuit. The converter also includes a first controller that is programmed to selectively operate for one converter limb at a time the primary switching element in each limb portion thereof to simultaneously switch both the first and second limb portions into circuit and thereby define a fully-conducting converter limb to sequentially route via each said fully-conducting converter limb a DC current demand (IDC) between the first and second DC terminals.