Integration of Z-Source Breakers Into Zonal DC Ship Power System Microgrids

The next-generation electric ships will feature a medium-voltage dc architecture for distribution of electric power. For higher reliability and flexibility, this dc microgrid is divided into zones each zone having its own protection and load center. The research presented in this paper explores how Z-source dc breakers can be integrated into zonal-based distribution microgrids. Specifically, this paper looks into the practical problems and solutions for running two Z-source breakers in parallel to supply current to the same load center. It is shown that the basic structure of two breakers in parallel can be replicated over a system with multiple zones to protect the entire grid. This paper presents a detailed look into the gate control of the SCRs in Z-source dc breakers. The path of the fault current for shunt faults created at various locations is traced. Using that information, a fault detection algorithm is presented and applied. The measured currents collected during faults and steady state operation will determine the gate signals for the SCRs. The postfault operation might include reclosing of a Z-source breaker if deemed necessary by the control. The simulation and hardware results verify the concepts proposed in this paper.