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Research on the current commutation in a novel hybrid HVDC circuit breaker

Recent development renewable energy increases the requirement in constructing multi-terminal HVDC systems or HVDC grids. To increase the system reliability, an HVDC circuit breaker will be required. However the existing HVDC breakers developed in recent years use large amount of IGBTs. Considering the cost reduction in real HVDC grids, this paper presents a novel hybrid HVDC circuit breaker. The proposed topology is based on anti-parallel thyristors and full bridge sub module technique with bidirectional interruption. In normal operation, the fast mechanical switch and small amount of IGBTs handle the low conduction loss. In case of interruption, the faulted current is forced to the snubber capacitor of transfer branch in order to turn off thyristors. The proposed breaker has significant technical advantage compared with other solutions especially in terms of current breaking ability and semiconductor cost. The modular unit design could improve the voltage application easily. Moreover, the voltage stress over the load commutation switch is analyzed based on a simplified model. It is observed that the parameters of snubber circuit and time delay of commutation time have great influence on the voltage stress. A principle prototype has been built and tested with an adaptive triggering board. A current commutation test procedure is developed to verify the voltage stress.