Abstract

The operation of HVDC systems using conventional Line Commutated Converters (LCCs) operating with weak AC systems becomes unreliable due to frequent commutation failures which can occur for any small disturbance in the AC networks. The thesis starts with a brief survey of the present state of the art in HVDC systems. This is followed by the descriptions of different subsystems of the CIGRE benchmark model. The basic control characteristics of HVDC systems are discussed and their implementations are described using block diagrams. Finally, different tests are carried out by applying varying faults and step changes in the control parameters. PSCAD/EMTDC simulation package is used to model the CIGRE benchmark and its various control circuits. The performance of the CCC is compared with conventional LCC using the same benchmark model. Finally, a modified version of CCC configuration, namely Hybrid Converter Combination (HCC) configuration is presented. This configuration uses a combination of both a traditional LCC and a CCC. Its viability is assessed in terms of technical suitability and lower overall cost