Voltage control for an HVDC convertor

A voltage control scheme for an HVDC convertor is proposed which uses bypass thyristor valves connected to tapping points on the secondary windings of the transformer. Fast and continuous control of the DC voltage is possible with good operational characteristics and low values of reactive volt-ampere absorption. The application to bidirectional and unidirectional power-flow schemes is examined, including the feasibility of operation without the conventional onload tap changer on the convertor transformer.