A VSC based series hybrid converter for HVDC transmission

The paper presents how voltage sourced HVDC converters can be added to an existing conventional Dc converter to enhance the power transfer capability and to improve the dynamic performance. The fact that the VSC converter can operate without reactive power support implies that the increase in power transfer capability can be achieved without the expenditure on additional compensation equipment. Moreover, the VSC can be controlled rapidly and has the ability to generate reactive power and hence maintain bus voltage making such a hybrid converter promising for operation into very weak AC systems. A control system suitable for operation into an ac network with a very low snort circuit ratio (SCR) is developed and the operation of the hybrid scheme is demonstrated using electromagnetic transients simulation