마이크로그리드의 재생에너지 이용률 확대를 위한 MVDC 연계 방안

Abstract

.Currently, some islands of South Korea are receiving electric power through the generation of distributed facilities. Distributed resources usually consist of wind turbine generator (WTG), photovoltaic (PV), energy storage system (ESS) and diesel generator (DG). When the power of renewable generatioin sources is larger than power loads continuously, the state of charge (SOC) in ESS reach the upper limit. And the power system operator of the microgrid limit the output of renewable energy. If the weather condition is deteriorating for long time, the DGs have to operate since the SOC is at the low limit. These problems decrease penetration ratio of renewable energy and have the environment pollution. To expand penetration ratio of renewable generation sources and stabilize the microgrid, this thesis proposes the introduction of medium voltage direct current (MVDC). The Gapado Island is selected as the model of microgrid site for applying the proposed method. DC line of the MVDC is connected with the Gapado Island to Jeju power system in order to make the best use of the established facilities. To verify the validity of introducing MVDC, the computer simulation with PSCAD/EMTDC program will be carried out three cases : First, the situation of WTG stop by the ESS SOC limit. Second, disconnection of connected battery line with back to back converter. Third, the appearance of a ground fault in Jejudo grid.