| As the growth of electrical load, the reliability and stability of power grid are reduced, the utilization ratio of energy is low,energy crisis and environmental problems are more and more serious, and electrical industry is facing greate challenge. In view of the above problems, distributed generation technologywith advantage of environment friendly, high efficiency and feasibility is researched in all countries. As a low voltage distribution network with different distributed generations, MicroGrid conbines generators, energy storage devices and load to a single controllable unit. It not only solves the problem of large-scale access of DGs, make full use of distributed generators, but also increases the reliability and stability of power supply, bring the users a variety of other benefits.Quality ofelectrical power supply can be seriously influenced due to the variety, intermittence and fluctuation of the power output and complicated control of DGs in MicroGrid, which is the key reason for keeping it from gird-connected. As a power energy buffer device, storage can improve quality of power supply, increase the reliability and stability of microgrid and make aimportant role in it. Different kinds of storage applying in power system are researched in the paper, including battery, flywheel,ultracapacitor, and so on. Operation mechanism, charge and discharge characteristic, application scope are eliminated in the paper, and dynamic modeling and simulation of the storages in MATLAB/Simulink can precisely imitate the action of the storage.Favorable control strategyis the foundation of various DGs in MicroGrid operating coordinately, MicroGrid can operate flexibly both in grid-connected mode and isolated mode, effective switch between the two modes. Different kinds of control strategies are designed in this paper. PQ control(fix power control) is used to make the inverter to supply a given active and reactive power set-point, V/f control can stabilize the voltage and frequency of the inverter, but it can only operate in isolated mode. VSI (voltage source inverter) is used to make the inverter to feed the load with pre-defined values for voltage and frequency,the out-put power of the VSIis automatically defined by the well known frequency droop characteristic. VSI control can operate both in grid connected mode and isolated mode. The bi-DC/DC converter of energy storage is used to connect storage and DC bus, enable the energy to flow in bi-direction and make the storage to follow the reference power. There are two control strategies for MicroGrids operation:SMO(single master operation) and MMO(multiple master operation). Two MicroGrids, one is the typical MicroGrid which contains 3 buses and 14 nodes, the other is the mode of a MicroGrid laboratory of Zhejiang electrical power test and research institution, are modeled and simulated,results show the correcthness and effectiveness of the control strategy proposed in the paper.Compound storage technology applying in smoothing the fluctuation of power output of wind-PV hybrid power system is researched in this paper. Optimizingcoordination control strategy such as variable time-constant control, maximum power limitation control for multi-type energy storage is proposed, which optimize the operation of storage components, reduce the demand for storage capacity and prove the economical efficiency of the hybrid system.To present the simulink models of DGs or MicroGrids in the mode of owing intellectual property rights, independent developed and operated.versatile software architecture is used to handle and pack these models,and MicroGrid numerical simulation platform is developed. This software can supply the flexible construction and the function of modifying parameters for MiroGrid, as while as interaction simulation with PSCAD. It can precisely simulate the operation of MicroGrid for observing the dynamic process of voltage, current, frequency and so on, and provide the basis for further research in MicroGrid. |
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