Research On Modeling And Control Strategy Of DC Micro-grid

Energy crisis promotes renewable distributed generation develop rapidly. Inorder to reduce the impact of distributed source that directly connected to the maingrid, a new microgrid combined of different distributed sources is typicallydeveloped and then it is connected to the main grid. AC microgrid is the mainstreamform, but with the increase of the DC load and the development of DC distributedpower source, AC microgrid is caused a lot of problems. If DC load and DCdistributed sources are directly combined as DC microgrid, it will bring lots ofbenefit, such as lower investment, better power quality and better systemcontrollability. And with the development of power electronic technology, DCmicrogrid can be controlled flexibly and the superiority will naturally be exerted.The structure of DC microgrid, the principle of power interface circuit and itscontrol method are deeply analyzed in the paper, and connected model of DCmicrogrid is constructed in Matlab/Simulink. For photovoltaic systems, MPPTbased on index variable step size perturbation and observation method, and constantvoltage control strategy are both proposed. For DC/DC interface, charge anddischarge control strategies are proposed to achieve a two-way battery charging anddischarging control model. Low-power direct-drive wind turbine simulation modelis applied to the system in the last step, and the studied DC microgrid is morepractical.There is no need to take frequency and phase into consideration in DCmicrogrid and voltage of DC bus is considered as the only indicator measure thestability of the system, so it is of great importance to keep the voltage of DC busstable. For photovoltaic systems, coordinated voltage control strategy is proposedand according to this, the operating state of DC microgrid is divided into three basiccategories. Based on bus voltage and SOC%(State of Charge), conversion betweenthe basic state is easy and both stability control and energy management can beachieved. Low power wind turbine is connected to the DC microgrid and its priorityto act as regulator is different in daytime and during night is taken intoconsideration. By this, voltage-control work of DC microgrid is fully achieved.Finally, simulation work is carried out and the results show that the proposedcoordinated voltage control strategy can ensure the stable operation and seamlesslyswitching between respective state of DC microgrid.