I. Introduction
Currently, with adaption to the new characteristics of power market, the concept of energy internet, through integration of the power grid with the internet information network, can greatly meet the multi-directional and complex trend of the future power grid as well as the personalized needs of users. According to the Future Renewable Electric Energy Delivery and Management (FREEDM) Project supported by the National Science Foundation of the United States, energy internet can be interpreted as a new type of power grid structure with a variety of load compositions. By comprehensively utilizing the advanced power electronic technology, the information technology, the intelligent management technology as well as the acquisition and storage technology of the distributed energy, energy internet enables two-way flows of energy, peer-to-peer exchange and sharing [1]–[3]. Combined with internet thinking, the classic energy internet is interconnected by several energy LANs, with each one consisting of the energy router, the power generation equipment, the energy storage equipment and the AC-DC loads, which can be operated either in a grid-interconnection mode or in an independent off-grid mode in a single LAN. At present, the six key technologies to be solved urgently by energy internet are: the advanced energy storage technology, the solid transformer technology, the intelligent energy management technology, the intelligent fault management technology, the safe, reliable and efficient communication technology as well as the planning and analysis technology of the flexible power grid system [1].