Transients in Electricity Networks with Distributed Generation

by Yunqi Wang

Institution: University of New South Wales
Department: Electrical Engineering & Telecommunications
Year: 2015
Keywords: Stability; Micro-grid; Transient
Record ID: 1050947
Full text PDF: http://handle.unsw.edu.au/1959.4/54266


Micro-grids are becoming very popular due to the plug-and-play nature of their integration. However, the high penetration of distributed generators (DGs) may also create potential instability due to the special characteristics of DG units and their low inertia. With the increase of DG penetration level, the overall dynamics of the power system may become significantly impaired. Thus, the increasing penetration of distributed generation into the electricity network presents new challenges for reliable operation of the whole system. This thesis investigates the micro-grid dynamic performance caused by different kinds of common disturbances such as sudden switching of Photovoltaic (PV) source, loss of a large system load and three-phase fault. The simulations and experiments are conducted in different micro-grid configurations. The critical clearing time (CCT) of the micro-grid under the three-phase fault condition is also discussed. The research results, from both computer simulations and laboratory experiments, show that the micro-grid transient performance is affected by a number of factors including micro-grid operation mode, energy storage capacity, DG penetration level and disturbance level. It is shown that the application of distributed generation can help enhance the micro-grid transient performance. However, it is difficult for the micro-grid to maintain stability under a disturbance without any energy storage as the characteristics of the DG make it incapable to adjust the system parameters during the transient. The DG power output may reduce, and in the worst situation, the protection will operate to isolate the DG from the micro-grid. This will lead to a loss of power generation and result in a more serious disturbance in the grid. The application of battery storage can improve the micro-grid transient performance considerably. The power rush can be absorbed by this device and the micro-grid dynamic response is substantially improved. However, the disturbance in the micro-grid is unpredictable and it is difficult to determine the capacity and location of the storage device, which are the two main factors that will affect the battery performance. The research also shows that the CCT of the micro-grid with multiple DGs is different from the traditional network with only synchronous generators. The CCT is affected by the DG penetration level, wind turbine protection insertion time and battery storage capacity level.