Research On Technology Of Grid-connection In DC Micro-grid With Distributed Generation

Energy is the material basis to support the progress of human civilization, and it is indispensable to the development of modern society. The development of China’s energy is faced with many challenges. Energy resource endowment is not high, per capita consumption of coal, oil and natural gas is low. In recent years, the growth of total energy consumption is rapidly, and the pressure of energy supply is increasing. Large-scale exploitation and utilization of fossil fuels is resulting in some degree of impact on the ecological environment. Man is now facing a huge historic change, its goal is that the use of fossil energy is transformed into the use of renewable energy.New energy is the inevitable choice to solve the problem of the human sustainable development. The development of new energy has become the consensus of all countries in the world. The wind and solar energy as a renewable clean energy have a good complementary to each other in time and space, wind-light complementary system has become a effective way to reasonably development and utilization of new energy. With the development of power electronic technology and control technology, DC micro grid has got the attention from all walks of life. Compared with AC micro grid, DC micro grid does not need to consider the phase voltage and frequency the operation of distribution network is more flexible and higher reliable.Based on the stable operation of the DC micro grid, all aspects of the Wind-Solar-Storage micro grid control strategy are studied in the paper. The study involves the system topology, maximum power point tracking(MPPT) methods of wind and PV power, the control strategy of inverter. And this paper has carried on the simulation the platform in the PSCAD environment, the simulation results are analyzed, which laid a foundation for the further study on the follow-up of the micro grid. The main study contents are discussed as follows:Firstly, we analyze the structure of DC micro grid and research the characteristics and the access mode of the distributed power supply. The relevant characteristics of the wind turbine, photovoltaic array and battery are analyzed which have laid a good theoretical foundation for the model establishment and the control strategy.Secondly, we make a detailed study of maximum power point tracking(MPPT) methods of wind energy and solar energy. In a photovoltaic module, based on the traditional MPPT control strategy, Cuckoo Search (CS) is proposed. It is acknowledged that CS exhibits several advantages which include fast convergence, higher efficiency using fewer tuning parameters and lower complexity. While we select the optimum torque which does not need to measure wind speed control as the maximum power point tracking strategy in the tracking method of maximum wind power point.Thirdly, a detail study on the problem of interface which include distributed power supply, DC micro grid and the AC network have been carried on. We put forward the corresponding control strategy for energy storage module and grid module, which lays a foundation for the further study of DC micro grid.Finally, for the whole of DC micro grid system, we have proposed a new hierarchical control strategy, and set up a corresponding simulation model of DC micro grid in the PSCAD environment, the model includes the PV module, the wind power generating module, storage module and network module and load module. The effectiveness of the proposed control strategy is validated through simulation.