Research On Energy Optimization Control Of DC Micro-Grid

Worldwidely speaking, successive accidents of large area blackout occurred in recent years, which fully exposed the fragility of large power system. Distributed energy (Distributed Generation, DG) has got much attention from many governments and become one of the trends of power system. However, there are still many problems in DG, such as higher cost of single access and more difficulties in control. In order to reduce the impact of DG to power grid, DG has to be limited and segregated so that DG cannot be given full play to their potential. For the sake of harmonizing the contradiction between power grid and DG and making full use of DG, the concept of micro grid is proposed.By integrating the micro power supply, load, energy storage devices and control devices, micro-grid become a single controllable independent power supply system. Its operation is flexible and have higher request for the control strategy. Among them, DC micro-grid, compared to AC micro-grid, has few power conversion links and higher efficiency, controllability and reliability and it don’t need to track the phase and frequency of the voltage. Hence DC micro-grid is more suitable for the access of DG and loads. Research of optimization control of DC bus is, as yet, very poor. How to uniformly and harmonically control the distributed generations in DC micro-grid, improve the energy utilization efficiency of DC bus, maximize the use of clean energy and realize the economic operation of the micro-grid are problems of important researching value that must be solved during the development process of DC micro-grid.Research has been conducted from three aspects:maximum power point tracking of DG, control of bi-directional DC/DC converter and power optimization control of DC bus. Main research achievements are as follows.(1)Give the simulation model of wind power generation using Matlab/Simulink, and analysis the output characteristics. And achieve MPPT of wind power generation with duty ratio perturbation method.(2)Give the simulation model of photovoltaic using Matlab/Simulink, and analysis the output characteristics. The variable step size disturbance maximum power point tracking method based on power prediction is presented and tested in the Matlab/Simulink environment.(3)Charging and discharging simulation model of battery is set up and the control strategy of bi-directional DC/DC converter is verified by simulation.(4)Energy optimization method of DC bus is proposed, which improves the energy utilization efficiency of DC bus through controlling micro sources working in the MPPT mode or bus voltage tracking mode. Take a wind/solar power system, for instance. Simulation result verifies the effectiveness of the proposed method...