Modeling And Control Strategy Researching Of A Micro Grid

Micro grid is a new kind of power system which developed on distributed generation. It's called micro grid because the area and the amount of components of a micro grid are both small. A self-contained micro grid should have such components as distributed generators, distributed energy storage system, loads, control system and other accessorial elements. The problem of islanded operation brought by distributed generation has been solved by micro grid, which is able to operate both in grid-connected operation mode and in islanded operation mode. Then the loads in a micro grid can always operate steadily whether the main gird is normal or broken down, in other words, the reliability of electrical power supply is improved by the micro grid.The control strategy of grid-connected operation and islanded operation of micro grid has been researched detailedly and deeply in this paper. When in grid-connected operation mode, the distributed generators in the micro grid should work in invariable power control mode to inject invariable active and reactive power to the main grid. and the generators which use green energy should work at the upper limit to make good use of green energy. The micro grid should come into islanded operation mode if some faults occur in the main grid. If the capacity of the micro grid is less than loads, a distributed energy storage system is needed to control the voltage and frequency to maintain the steady work of loads at the beginning of islanded operation, and the distributed generators are still work in invariable power control mode in this period. If the energy of the distributed energy storage system exhausts but the micro grid hasn't reconnect to the main grid yet, the minor loads and distributed energy storage system should be cut off from the micro grid, one distributed generator with a higher capacity and faster response rate should switch to work in voltage/frequency control mode, other generators are still work in invariable power control mode. The micro grid should get back to grid-connected operation mode after the faults in main grid disappear, and the distributed energy storage system should recharge to get ready for the next islanded operation.A simulation model containing main grid, distributed generator module, distributed energy storage system module and loads is modeled in Matlab. The convertor is the interface of distributed generators and energy storage system, and all the control strategies are implemented on the convertor too. The results show that the conclusion of control strategy of this paper is feasible, and the operating performances of grid-connected operation, islanded operation, and the transition process of these two modes, are all good.