A new hybrid multi-level Voltage-Source Converter with DC fault blocking capability

Voltage-Source Converters have brought numerous advantages to HVDC transmission. However, they suffer from high losses and are usually weak against faults on the DC-side. In this paper, a new topology which brings together some concepts from traditional Current Source Converters and multi-level converters, is presented. Two stacks of H-bridge cells alternate to construct the converter voltage using director switches made of IGBTs in series. The resulting converter generates AC current with low harmonic content and with low loss. Furthermore, the converter is still very responsive in case of a fault. This paper first explains the composition and the working of this converter, then detailed simulations at 20 MW illustrate the performances and low losses of this converter under normal conditions. The ability of this topology to deal with abnormal conditions is also demonstrated, especially its ability to keep control of the current despite the collapse of the DC bus voltage, e.g. a DC-side fault.