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Most of HVDC systems consist of line commutated converters. The demand of reactive power is supplied by filter or capacitor banks which are connected on the primary side of the converter transformer. This conventional design is well known and proven during last decades. However, such conventional converters suffer commutation failures when they operate as inverter at a weak AC system. A series capacitor between converter transformer and thyristor valves (CCC: Capacitor Commutated Converter) can improve the immunity of inverter against commutation failure. Two concepts for the transmission with a high power capacity using HVDC technology are compared in this paper. These include the conventional and the CCC-inverters, connected to weak AC systems. The simulation results are presented using MATLAB/SIMULINK.