Voltage source converter

A voltage source converter comprising first and second DC terminals for connection to a DC electrical network, the voltage source converter further including a plurality of limbs connected between the first and second DC terminals, each limb including:

• a phase element including a plurality of switching elements to interconnect the DC electrical network and an AC electrical network;
• and
• an auxiliary sub-converter configured to be controllable to act as a waveform synthesizer to modify a first DC voltage presented by the limb to the DC electrical network,
• wherein the voltage source converter further includes a controller configured to selectively control each auxiliary sub-converter to modify the respective first DC voltage to include at least two auxiliary harmonic components, each auxiliary harmonic component being a positive integer multiple of a 2nd harmonic component.

A voltage source converter comprising first and second DC terminals for connection to a DC electrical network, the voltage source converter further including at least one limb connected between the first and second DC terminals, the or each limb including:

• a phase element including a plurality of switching elements to interconnect the DC electrical network and an AC electrical network;
• an auxiliary sub-converter configured to be controllable to act as a waveform synthesizer to modify a first DC voltage presented to the DC electrical network;
• and
• a tertiary sub-converter connected with the phase element in an electrical block, the auxiliary sub-converter being connected in parallel with the electrical block, the tertiary sub-converter being configured to be controllable to act as a waveform synthesizer to modify a second DC voltage presented to a DC side of the phase element,
• wherein the voltage source converter further includes a controller configured to selectively control the or each tertiary sub-converter to generate a compensatory DC voltage component for presentation to the DC side of the or the respective phase element so as to compensate for a change in real power and/or reactive power generated or absorbed at an AC side of the or the respective phase element.

A voltage source converter comprising first and second DC terminals for connection to a DC electrical network, the voltage source converter further including at least one limb connected between the first and second DC terminals, the or each limb including:

• a phase element including a plurality of switching elements to interconnect the DC electrical network and an AC electrical network;
• an auxiliary sub-converter configured to be controllable to act as a waveform synthesizer to modify a first DC voltage presented to the DC electrical network;
• and
• a tertiary sub-converter connected with the phase element in an electrical block, the auxiliary sub-converter being connected in parallel with the electrical block, the tertiary sub-converter being configured to be controllable to act as a waveform synthesizer to modify a second DC voltage presented to a DC side of the phase element,
• wherein the voltage source converter further includes a controller configured to selectively control the or each tertiary sub-converter and/or the or each auxiliary sub-converter in a fault operating mode so as to minimise a fault current flowing or block a fault current from flowing through the voltage source converter when a fault occurs, in use, in the DC electrical network.