Devices Selection and Topology Comparison for Medium Voltage DC Solid State Circuit Breakers

Abstract

DC grid has been treated as a viable solution to solve green-house effect and reduce the cost of fossil fuels. Compared with AC grid, DC grid shows many inherent advantages, such as high efficiency power delivery, less expensive to deploy and no need for phase and frequency synchronization. However, over current protection for DC grid require fast response. To solve this problem, solid state DC circuit breakers need to be promoted. In this thesis, thermal property was taken into consideration to find the most suitable semiconductor devices. Per unitized thermal resistance of the heat sink to the ambient was used to find the reasonable conducting current. Module MOV topology and one MOV topology were compared to see the voltage and current stress ANSYS Simplorer is used to assist in the process. Simulation is used to see the waveform of the current stress and the voltage stress under ideal and non-ideal condition. According to the results, during the ideal condition the current stress and the voltage stress are almost the same. However, under the non-ideal condition, the current stress and voltage stress are different, and the module MOV mode topology is much more reliable and has less current and voltage stress.