| With a large number of wind farms connected to the power system,the modern power system has been transformed into a random-deterministic coupling system.Unlike the regulation of conventional thermal power,the randomness and fluctuation of the output of wind power system may bring more adverse factors to the regulation and control of power system operation.The influence of this random fluctuation on the small interference stability of power system with wind power is also huge.However,the traditional stability analysis methods have some limitations on the stability impact caused by this random fluctuation.It is necessary to study with the theory of stochastic differential equations,which is still weak.Therefore,this paper studies the small disturbance stability of power system caused by wind power random fluctuations caused by wind speed fluctuations.In this paper,stochastic differential equations and stability theory are combed.Wind power fluctuation is modeled dynamically by using the Wiener process,and the mechanical power fluctuation input by asynchronous fan is considered as random excitation.Considering the coupling function relationship between the random fluctuation of wind power and the random part in the coefficient matrix of system state equation,a small disturbance stability analysis model of power system considering the fluctuation of wind power is established based on the Ito type time-varying stochastic differential equation system.It lays a foundation for the subsequent analysis of small interference stability of wind power system.Secondly,the small disturbance random stability mechanism and analysis method of wind power system with random coefficients of state equation under wind power fluctuation are explored,and the mean square stability of wind power grid with random coefficients is equivalent to that of deterministic system.A random mean square stability criterion and a calculation method of mean square stability probability for asynchronous fan-connected system considering wind power fluctuation characteristics are presented.At the same time,an improved EM numerical method is used to solve the random stability analysis model,and the relationship between wind power fluctuation intensity,mean square stability dividing interval and mean square stability probability is obtained.The criterion is verified by simulation.The validity of the calculation method based on the mean square stability probability.Then,the factors that affect the oscillation probability of the fan parallel-connected system are analyzed,and the conclusion that the line parameters and stator reactance are the dominant factors is obtained.An additional filter to reduce the oscillation probability is presented for the dominant factor.At the same time,the quantum-behaved particle swarm optimization is introduced to optimize the filter parameters with the maximized system stability dividing interval as the objective function.Finally,the validity of the proposed oscillation probability suppression method is verified by a three-machine nine-node simulation example. |
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