| As the environmental and energy situation become more and more serious, DG technology has got powerful development, however, its drawbacks such as uncontrollability also bring disadvantages to the Smart Grid that limits its own development ,while the micro-grid can solve the problem. The micro-grid is a kind network combined by various DER to provide electric power for the load. The DER is one of hot research topics at home and abroad, it is near the load ,so it mainly choose the low voltage level. Considering the limitations and complexity to establish a experimental micro grid, the model of micro grid is generally established by simulation software to do the research of the micro-grid's protection, operation control, planning, and etc. The DER was connected into the micro grid by power electronics port that increases the flexibility control requirements of DER port. Many factor such as the various operation state of micro grid make it more difficult to sustain frequency stability and keep the energy balance. How to connect different types DER and form the micro grid? How to realize reasonable control? Both of these are problems which must be soved.In this thesis, the construction cost, operation flexibility and the reliability of micro network are all taken into account. Then, the initial wiring schemes are chosen. Studied three control methods of microsource, that is Droop control, frequency voltage (VF) control and PQ control, and analyzed their different structures. Cases of droop control and mix control are simulated in PSCAD, the results show that Micro-Grid can keep its stability during isolated, and thus prove the effectiveness of control schemes. The microsource need to readjust its output when Micro-Grid reconnect to the main grid under any control scheme, thus can ensure a smooth transition of Micro-Grid operation mode. |
