Research On Energy Micro Grid Control System Based On The Structure Of FREEDM

Due to the depletion of fossil fuels and global warming, the development of human has been limited. To solve this problem, on the one hand, the Chinese and foreign scientists are looking for sustainable, clean and renewable resources to generate electricity; on the other hand, researchers in worldwide are studying how to effectively coordinate and make use of intermittent energy relying on the control technology, communication technology, energy storage technology and power electronics technology. Speeding up the construction of Energy Internet and overcoming the technical bottlenecks can effectively combine a variety of new energy together and make them available for human. This can address the growing energy and environmental issues, which has a great significance for human subsistence and development.Energy Internet is a paramount invent related to human’s subsistence and development. Because the Energy Internet is a grand and long-term development plan, in this article, only one micro-network is chosen and built model for. This paper is based on the FERRDM system, and a computer network control system is analogized to construct the micro-grid energy FREEDM structure.Firstly, the paper introduces the FREEDM system’s composition, technical characteristics, solid state transformers’ principles, and intelligent energy management system. It also mentions the principles and classifications of several current important distributed renewable energy, some energy storage devices and an assumption based on the large-scale renewable energy system, the FREEDM system, then analogies this system with the computer network. Under the FREEDM system, the topological structure of the energy micro-grid is built using the photovoltaic arrays, wind power and energy storage element as distributed power.FREEDM system includes solid state transformers, intelligent energy management and distributed renewable energy, distributed energy storage devices and load. In this paper, solid transformer is the core of the FREEEDM system mainly including AC/DC single-phase rectifier module, isolated DC/DC converter module and DC/AC three-phase inverter module. The transformer is modeled and the control strategy for each module is determined in this paper. It also studied the principles of photovoltaic cells, wind power systems and energy storage device, and built their equivalent model.Secondly, we studied two typical operation modes of the Energy Internet---the grid-connected mode and island mode, two methods to control with single micro-power-----PQ control and V/f control and two strategies to control micro-grid energy----master-slave control and peer-to-peer control. and we select the appropriate control strategy for this design according to the actual demand and the model.Finally, in this paper, we have built a simulation model for the solid state transformer, simulated and analyzed its AC/DC single-phase rectifier module, isolated DC/DC converter module and DC/AC three-phase inverter module. Built a math model based on physics theory of PV cell and analyze its voltage current characteristic. Take photovoltaic cells for example, we have simulated the single-phase photovoltaic grid, and obtained the PV output voltage curve, DC voltage curve after boosted and maximum power curve; established the simulation model of renewable power integration based on FREEDM system, gotten high voltage DC bus voltage, transformer’s primary voltage, transformer’s secondary voltage, low voltage DC bus voltage and the inverter’s current waveform. According to the topological structure of the FREEDM system, we have established a simulation model of the solar and wind storaging micro-grid, and simulated the model under the islanding operation mode and grid-connected operation mode.