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There is a highly-increasing demand for the DC power transmission and distribution in modern power systems for the integration of newly-installed renewable energy resources and storage systems to the existing utilities. Application of DC power systems in electric ships, battery energy devices, high-voltage DC networks, smart grids, electric vehicles, microgrids, and wind farms is a recent trend that is being highly investigated. The fault protection of DC systems is an essential but challenging issue that needs careful attention to maintain system operation reliability and device safety. In this research, the specification, control, and application of Z-source breakers (ZCBs) are investigated for DC network protection. Initially, the power loss associated with the topology of ZCBs is a key consideration in the design, and thus, the most efficient ZCB topology is identified. In this study, the topology of inter-cross-connected bi-directional ZCB (ICC-BZCB) was selected due to its least power loss when operating in a steady-state condition. Based on ICC-BZCB, a new approach of parameter specification is proposed by considering the reverse-recovery time of thyristors. The proposed approach ensures the turnoff action of ZCB in practical application. Its effectiveness was verified by experimental tests on a hardware testbed in the laboratory. Secondly, a new method of specifying the Z-source capacitances is proposed to identify the high-impedance faults in DC power networks. The method defines the principle of HIF detection and interruption by monitoring the status of Z-source capacitances. Finally, the assessment of cable length limit for ZCB application is analyzed for the DC system applications. |
