This paper presents a detailed comparison between two voltage source converter high-voltage dc transmission systems. The first is based on the neutral point-clamped converter (also known as HVDC-Light) and the second is based on a modular multilevel converter (known as HVDC-Plus). The comparison focuses on reliability issues of both technologies, such as, fault ride-through capability and control flexibility. To address these issues, the neutral point-clamped and three-level modular converters are considered at both stations of a dc transmission system. Several operating conditions are considered, including, symmetrical and asymmetrical faults. Computer simulation is used to confirm the validity of the results.