Analysis On Static Voltage Stability Of Isolated Micro-Grid Based On Bifurcation Theory

In recent years, there have been many large areas of power outages in the world, which makes people’s dependence on traditional large power networks become low. With continuous improvement of the new energy and the growing popularity of the power generation technology, a new distributed power generation (microgrid) has been recognized, and voltage stability problem has always been the power system’s basic problem, so the microgrid’s research of voltage stability problem has a important significance.The bifurcation theory is applied in the isolated micro grid to analyse its static voltage stability in this paper. The saddle node bifurcation point is used as the voltage collapse critical point, using continuous power flow (CPF) algorithm to analyze the voltage stability of a small isolated micro-grid with four nodes, then tracing the equilibrium solution manifold curve of the system, and according to the characteristics of the root to determine whether there is a saddle node bifurcation point in the curve. A small isolated microgrid system is built, then establishing the mathematical model of each node, and the node types are classified. The load growth factor is as the control parameter to analyse the effect of different load model on the static voltage stability of microgrid, the simulation shows that the system with constant power will lose voltage stability easier than second type of dynamic load. For analyzing the voltage stability of the micro grid system with wind farm, the input active power of the wind turbine is controlled as a parameter to trace its equilibrium solution manifold curve. The experiments show that when the wind power generator terminal without shunted reactive power compensation device, with the increase of the input active power of the wind turbine, the micro network system’s saddle node bifurcation point will occur, if we continue to increase the output power, the system will lead to the phenomenon of voltage collapse; The static voltage stability of the system will be improved after the reactive power compensation device is connected in parallel with the generator of the wind generator; In addition, the stability of the micro grid system can be improved by the wind-solar hybrid.The stability limit of the reactive power compensation and non reactive power compensation system voltage are calculated respectively, to obtain the voltage stability margin of load node, and two kinds of reactive power compensation devices are compared:the effects of SVC and STATCOM on the voltage stability margin of the system are analyzed. The experiments show that the voltage stability margin of the system can be improved after adding the reactive power compensation device and the power output limit of power generation can be improved. At the same time, because of reactive power output characteristics of the STATCOM, which is more effectively than SVC in improving system voltage stability margin and delaying the occurrence of saddle node bifurcation point, then improving the system voltage stability margin.