Research On Smart Microgrid Protection Method Based On Wide Area Information

Climate change concerns due to the rising amounts of the carbon gas in the atmosphere have in the last decade or so initiated a fast pace of technological advances in the renewable energy industry. Such developments in technology have made renewable resources based Distributed Generators(DGs) more desirable. However, it is a known fact that rising penetrations of DGs have adverse impacts on the grid structure and its operation. The microgrid concept is a solution proposed to eliminate the adverse impacts of DGs and make conventional grids more suitable for large scale deployments of DGs. Unlike traditional distribution network, microgrids are designed to operate in one of two modes, grid connected and islanded. Short circuit levels in islanded mode tend to be small compared to those in grid connected mode. Moreover, power flows in microgrids are not always unidirectional. For these reasons, it is difficult to protect microgrids using relaying strategies traditionally used in distribution systems.A three-layer smart microgrid protection method based on wide area information is proposed based on in-depth analysis of fault feature under grid-connected and islanded mode. The protection system consist of microgrid protection center(MPC) and local protection unit(LPU). The decision-making process of main protection is centralized. MPC makes a comprehensive decision according to the measurement information uploaded by LPUs and sends a trip signal. A decentralized backup is proposed in case that the trip signal is lost. LPU considers the main protection fails and exchanges information with LPUs in its communicating area and makes a protection decision. In case of communication system failure, a backup protection method based on local information is proposed. LPUs discriminate the fault element based on local measurements and trip the corresponding circuit breakers to complete the fault isolation.Finally, a medium-voltage microgrid model is established in the Matlab/Simulink software to verify the feasibility of the protection method under different operating modes and different types of faults.