Study On Analysis And Control Strategy For Power Sytem With Large-scale Wind Power

The increasing scale of power grid and wind power integration has made the analysis,operation and control of the power system more complex.On the one hand,the interconnections of regional power networks and the high voltage,long-distance,high-capacity power transmission mode make a great change in the power grid's characteristics compared with the previous condition.The complexity and nonlinearity of power grid have been greatly enhanced,bringing new risks to the security and stability of the power grid.On the other hand,with increasing wind power penetration,the performance of power system is no longer only influenced by controllable synchronous generators,but also a large number of stochastic and fluctuating asynchronous generators(wind turbine generators,WTG),which changes the modern power system into a complex stochastic-deterministic coupling power system.In this complex power system,complex coupling and interaction exist between wind turbines and conventional units,making the damping characteristic of the power system change greatly due to the huge difference between the wind turbine and conventional power unit.Meanwhile,the wind power's random fluctuations make the stability of low-frequency oscillations in power system also show the nature of randomness.In this case,the study on the impact of power system's nonlinearity and large-scale wind power's integration on low-frequency oscillations has important theoretical and practical significance.Therefore,combining the long-distance,high-voltage transportation characteristics of wind power and surrounding the impact of power system's nonlinearity and large-scale wind power's integration on low-frequency oscillations,this dissertation explored the mechanism of low frequency oscillation considering the nonlinearity and the analysis,warning and control of power system with large-scale wind power integration.The primary contents and original contributions of this dissertation are as follows:1.Concerning some low frequency oscillations in the power system which features low frequency oscillation with positive damping,the influence of nonlinear factors on the low frequency oscillation in power system is pointed out and the dynamic damping effect is put forward on the basis of the actual power-angle curve considering damping power and the study of damping torque's nonlinearity in this article.That is,in the process of oscillation,damping will dynamically change and will be less than that at the stable operating point especially when the angle of the stable operating point and the oscillation amplitude are larger.Based on this viewpoint,the explanation is put for these unknown low-frequency oscillation phenomena which may provide new ideas for the analysis and control of some low frequency phenomena with unknown mechanism.2.As for the impact of large-scale wind power integration on the damping characteristics of low-frequency oscillation,adopting catastrophe theory,we established a small signal stability region boundary model of an interconnected power system with large-scale wind power in two-dimensional power injection space and extend the 2D model to multi dimensions to obtain the small signal stability region boundary model in multidimensional power injection space.Based on these models,using the model of wind farm integration to the single-machine infinite bus power system,this paper studies the impact of wind power integration scale and the coupling strength with synchronous generator on small signal stability through the comparison of the stability region boundaries.The research in this paper greatly expands the view of the previous research,thus its result offers a good interpretation to the contradiction of previous studies from a qualitative point of view.3.On account of the random fluctuation characteristics of wind power output,the multi-scale low-frequency oscillation instability probability is studied based on Markov chain.Firstly,the basic principle of Markov chain was introduced,based on which we studied the uncertainty of wind power by adopting the transition matrix and the wind speed-power output transformation model and established the probability distribution model of multi-scale wind power.Then the boundary-based small-signal stability instability evaluation method was used to establish an evaluation model of multi-scale low-frequency oscillation stability probability of power system with wind farms.Compared with the previous studies,the transfer characteristic of the wind speed was stress-considered and the instability probability of multi-scale can be analyzed.The study of this paper greatly expands the time scales of past research and provides a new method and support for analyzing the low frequency oscillation instability probability of power system with wind farms.4.Based on the previous three parts of research,a new warning and control strategy for low-frequency oscillation was proposed in this article.Aimed at power system with large-scale wind power,based on small signal stability region boundary and considering the uncertainty of wind power,two low frequency oscillation warning indicators were proposed:stability margin and the probability that the power system loses stability at the next moment for rapid warming and to provide corresponding control strategy for certain operation mode.Compared with the previous studies,the low-frequency oscillation of warning and control strategy proposed in this article have faster computing speed,better adaptability for various operation modes and has the ability to effectively evaluate system's operation condition and give reasonable control strategies if necessary.