| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 97 === The application of DC distribution system combined with power electronic techniques is the way to solve energy issues. In addition, the amount of energy consumption in data centers is always an issue worthy to be considered. The advantage in DC power system lies on the features of transmission efficiency within low distance or high voltage. Higher transmission efficiency can be achieved due to the absence of reactive power. There are kinds of products which adopt digital electronic loads or variable-frequency motors in order to enhance the performance. Since most renewable energy generators like solar cell and fuel cell, AC/DC conversions stages can be saved while applying to DC system.
In the DC distribution grid, when grounded fault is detected at load side or distributed generation side, the DC circuit breakers should provide a fast interruption capability for the fault current and prevent the local grid from collapses. DC circuit breakers can be categorized into mechanical and solid-state types. The mechanical types have the advantages of low conduction losses, but the mechanical turn-off time is long so that the fault current is larger. For this reason the devices should be chosen at higher rating and have the capability to extinguish the occurring arc. The solid-state types have shorter turn-off time and no occurring arc. However, while a semiconductor device is used as main switch, the conduction loss is large which leads to thermal problems. The AC mechanical circuit breakers are available on the market. However, the design of circuit breakers for DC distribution system is a challenge compared with AC circuit breakers due to the absence of natural zero crossing. Therefore, in this thesis, except that the feasibility of DC distribution systems will be discussed, some topologies of DC circuit breakers in DC environment are proposed with the verification by simulation and experiment results.
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