인버터 기반 독립형 마이크로그리드의 고장전류 보호시스템

Abstract

Faced with environmental issues, many countries around the world have changed their obligations to reduce greenhouse gases, which were only applied to advanced countries, to a universal system in which all countries participate in reflecting their circumstances through the Paris Agreement in 2015. As a result, renewable energy resources are being installed in microgrids such as islands. One of the ways to increase the penetration rate of renewable energy resources in a stand-alone microgrid is that the ESS generates a reference voltage through CVCF controller. However, this method can't supply the fault current in the event of a phase to earth or phase to phase short circuit fault. Therefore, the protective relays are impossible to operate. In this paper, a protection system is proposed that only the fault feeder can be eliminated in the event of an asymmetrical fault when ESS generates a reference voltage. The proposed protection system can only eliminate fault feeder through low voltage and negative sequence current when over current is generated by a fault. The PCS outputs a low voltage when an over-current is measured and determines if the fault has been resolved through the negative sequence current. The feeder's protective relay is opened when a low voltage and the negative sequence current are detected. This method requires no communication between the PCS and the protective relay, and protection cooperation can be established by the user. To verify the proposed protection system, a stand-alone microgrid was modeled through the PSCAD/EMTDC program. The simulation was performed by dividing cases by phase to earth and phase to phase short circuit fault.