Investigate advanced approaches on direct current solid-state circuit breakers

Reza Kheirollahi

doi:10.17918/00001662

Direct current (dc) power systems are gaining more attention in academia and industry due to their advantages compared with conventional alternating current (AC) power networks. DC systems present higher efficiency at the same voltage levels, they need no frequency synchronization and reactive power compensation, and they ease the integration of renewable energies. Despite the advantages of dc power systems, there are still several technical and practical challenges that slow down their widespread adoption and development worldwide. One of the primary technical challenges that must be addressed is the development of dc circuit breakers (DCCBs). Among DCCBs, dc solid-state circuit breakers (SSCBs) use semiconductor devices to conduct load currents during the normal operation and hold dc bus voltages during the breaker OFF-state. Among many benefits, SSCBs present an ultrafast response speed, a modular structure, no arc problems, extended operation cycles, and a high compactness, fulfilling the urgent needs of emerging technologies such as electric ships. However, solid-state switches used in SSCBs have limited voltage/current turn-off capability and thermal capacity, requiring more investigations in the field. This thesis focuses on advanced techniques to enhance lifetime, safety, and reliability in dc SSCBs. There are four main contributions as follows. Firstly, soft turn-off dc SSCBs are introduced, where compact and fast active injection circuits (AIC) are used to eliminate the transient energy and mitigate gate voltage oscillations in solid-state switches during current interruption, extending the SSCBs lifetime. Second, active snubbers in dc SSCBs are discussed, and novel topologies are presented to extend the maximum allowable dc bus voltage on SSCBs, remove the voltage on passive components during the SSCBs OFF-state, and solve the reliability issue of varistors in SSCBs. Next, fault current bypass-based dc SSCBs are proposed, where fault currents are reduced to zero at the load side or faulty sections within microseconds regardless of the dc system's line inductance, improving safety. Finally, SSCBs are studied at the system-level, and a new protective scheme is developed to optimally coordinate dc ultrafast SSCBs in multi-source dc microgrids. In summary, dc SSCBs play a key role in newly established dc power systems. SSCBs present a fast response speed, a modular structure, and high compactness. In this thesis, advanced techniques are introduced to improve lifetime, safety, and reliability in dc SSCBs at device- and system-level.

Investigate advanced approaches on direct current solid-state circuit breakers

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Investigate advanced approaches on direct current solid-state circuit breakers

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