SILICON CARBIDE JFET BASED SOLID STATE CIRCUIT BREAKERS FOR MEDIUM VOLTAGE DC SYSTEMS

In application areas such as data centers, electric ships and dc microgrids, dc systems are better systems than ac counterparts, however lack of a fast, reliable and cost effective dc circuit breaker is a big obstacle on the way of development and wide usage of these kind of systems. Nowadays since the demand for electric power and especially, access to renewable energy sources such as solar thermal generation which are located in deserts and off-shore wind power, continuously increases the demand and interest in High Voltage Direct Current (HVDC) and Medium Voltage Direct Current (MVDC) systems. In order to accept and rely on such systems, availability of fast and robust circuit breakers is inevitable which makes them one of the key enabling technologies. This thesis introduces a novel design for solid state circuit breakers (SSCB) for MVDC systems. This SSCB is inactive during normal operation and when a fault occurs, by getting power from the fault condition will be triggered on and clear the fault. This SSCB is consisted of a fast startup flyback-forward converter as a gate driver and two normally-on SiC JFETs as the main static switches which share the bus voltage equally during the fault condition. The operation principles of the SSCB are explained and analyzed in details. Moreover, prototypes are built and tested in short circuit tests. As observed in real test and experiments, the circuit breaker prototype can interrupt short circuit fault current up to 150 amperes at a dc bus voltage of 1000 volts within 3 microsecond.M.S. in Electrical Engineering, July 201