Research Of Coordinated Control Strategy Between Grid-connected And Island Mode For The DC Micro-grid

As a new method to solve the traditional power problems,the micro-grid technology has developed rapidly in recent years.With a large number of DC loads and DC interface units access,the DC micro-grid gradually become the focus of research.Firstly,the topology of the DC micro-grid with photovoltaic and energy-storage is analyzed.And the energy-storage and photovoltaic is modeled respectively.Then these models are proved to be consistency with the theory according to the output characteristics of the photovoltaic and energy-storage by the simulation.Secondly,each interface converter is studied.In view of the stability control of the system under the isolated mode,the double closed loop control strategy of the energy-storage is proposed.Considering making full use of solar energy,the MPPT control strategy of the photovoltaic is taken.And in order to achieve the energy flow between micro-grid and power grid,the double closed loop voltage regulation based on the coordinate transformation is adopted for grid connected converter.Then to reduce the harmonics pollution of the power grid,the grid filter is designed by using trial and error.The thesis makes further research on the coordinated control of the DC micro-grid.In order to solve the problem that the traditional coordinated control strategy based on the DC bus voltage makes controlling errors,the coordinated control strategy based on the energy management system for the grid-connected mode and the island mode is designed.And then several operation modes of the system are analyzed;the running states of each micro power source are established under these modes according to the energy management system.The effectiveness of the proposed control strategy is verified by simulation.Lastly,the thesis analyze that the parameters of the traditional PI controller keep constant,which makes difficult to adapt to the time-varying system,and also this traditional PI controller does not have the ability to resist periodic disturbance.Considering that fuzzy control can deal with the time-varying and nonlinear systemwhose accurate mathematical model is difficult to establish,the adaptive fuzzy PI control strategy is designed to improve the traditional control strategy.And the results show that the improved strategy has a better performance on the stability control of the system,and also reduce the harmonic pollution and improve the robustness of the system.