Z-Source Circuit Breaker for DC-Network Protection

Direct current (DC)-nature distributed energy resources like solar and fuel cells are emerging in electric power systems as a part of DC microgrids/nanogrids, MVDC and HVDC transmission and distribution networks. DC microgrids, which is considered as coupling points of many renewable energy resources and distributed generators in modern power systems, cannot be widely applied until appropriate solutions of fault current limitation and interruption are proposed. But limitation of fault current in DC network is an essential challenge that needs careful attention. Due to the lack of a zero-crossing point in DC unlike alternative current (AC), most of commercial AC circuit breakers cannot be applied into DC power systems directly. A couple of Z-Source circuit breaker (ZCB) topologies have been introduced with capabilities of bi-directional power flow and automatic/controllable turnoff. In this work, the power loss analyses of three bi-directional ZCB topologies during normal steady-state operation have been performed. From our study, the Z-Source breaker with least losses has been considered and its power loss distribution which is a major consideration in breaker selection, along with its configurable tripping time is evaluated. By performing comparative study, we found that the inter-cross connected bi-directional ZCB has the minimum loss during steady-state operation. The relationship between steady-state power loss and configurable tripping time is determined by specifying the parameters of ZCB. It is found that the increase in configured tripping time would decrease the efficiency of ZCB relatively. From theoretical analysis and laboratory tests, it has been verified that when the tripping time is configured to be equal or less than 0.1 ms, the ZCB can operate at a high efficiency (say \u3e 98%), which makes it a good candidate for DC protectionhttps://digitalcommons.odu.edu/engineering_batten/1005/thumbnail.jp