| With large scale and high installed capacity of wind power integrated into the grid, the wind power has became one of the important and mature power technology. With a large amount of wind power replacing conventional energy, it has been reduced the consumption of conventional fossil energy and made the power system a step closer to the direction of green and low-carbon. But due to the stochastic volatility of itself, the change of wind may not be a constant speed. Different speed of wind lead to different input power and has different effects on the power system. At the same time, the potential ramp event of wind power could have resulted in power fluctuation, which not only brought some risks of normal operation of power grid, but the power voltage collapse would happen in a more risk situation. In this thesis, a typical three-node power system model consisting of the flexible dual mass model of wind power generation has been established and taken to study the influence of bifurcation in different wind speed, using the bifurcation analysis software AUTO 07.In this thesis, the bifurcation of DFIG has been taken to study in different speed of wind. The thesis selected the reactive power as the bifurcation parameter to analyze the bifurcation of DFIG by setting different input power under different winds. The thesis has found that different bifurcation points would appear under different speed of wind, not only the traditional Hopf bifurcation, ordinary static bifurcation or saddle bifurcation have been researched, but also Fold bifurcation point has been found through using the AUTO 07. The results have showed that different speed of wind has different impact on the voltage stability of the system when the DIFG parallels in the grid. When the speed of wind increase to a high value, the system is more likely to occur dynamic instability and the endurance ability of reactive power of power is also reduced.At the same time, this paper has studied the stability of the wind power when the ramp-up event of the wind power happens. Ramp threshold was defined by ramp rate and used the ramp threshold to distinguish the seriousness of the ramp event. Because the expression of threshold was not continuous, the thesis innovatively uses the mathematical methods to reduce the dimension of equations and introduce the mathematical model into the whole system. By analyzing the influence of different threshold on power system, the effects of ramp event have been judged. The results have showed when the ramp events happen, the system will be instability more easily than a constant wind state. The Hopf bifurcation will occur more easily when the system is offered in a high ramp rate, leading the system to a dynamic instability. The safety of power system would have declined when the system work on a high ramp rate.It will lead the system to stay in a dangerous state. |
