Research On Low Frequency Oscillation Modes And Influencing Factors Of Wind Power Regional Power Grid Based On EWT And Improved Prony Algorithm

Large-scale wind farms are integrated into the power grid instead of traditional synchronous generators.The access of wind farms will not only reduce the inertia of the system,but also change the power flow path and the interaction with the existing synchronous motors to affect the power system.Therefore,the stability problem of the high wind power penetration rate power grid is far more serious than that of the traditional power grid.At the same time,due to the increase of random fluctuation and uncertainty of wind power,the transmission power range of the tie line between regional power grids is expanded,and the low frequency oscillation mode identification of the regional power grid including wind power The methods and influencing factors need to be studied in depth.(1)This article first introduces the mathematical model of doubly-fed wind farms,and then introduces the mechanism of low-frequency oscillation and its analysis methods,and uses empirical wavelet transform to solve the problem of Prony algorithm’s sensitivity to noise when identifying low-frequency oscillations(EWT)combined with the improved Prony algorithm to identify low-frequency oscillations.EWT is a new adaptive decomposition algorithm.It first decomposes the noisy low-frequency oscillation signal through EWT to obtain the low-frequency oscillation modal components,and then reconstructs to achieve the filtering effect.Then the Prony parameter identification is performed on the filtered low-frequency oscillation signal.The results show that the EWT algorithm has better anti-noise ability,and the improved Prony algorithm has good identification accuracy.(2)This paper uses different examples to verify that the identification accuracy of EWT combined with improved Prony algorithm is better than EMD combined with improved Prony algorithm and directly used Prony algorithm.Next,this paper conducts a simulation analysis on the impact of large-scale wind farm integration on the low-frequency oscillation of the power system.The doubly-fed wind turbine(DFIG)is connected to the four-machine two-region system,and the inertia change and wind power of the regional power grid with wind power are studied.The impact of power fluctuations on the low-frequency oscillation of the system as the transmission power of the system tie line changes.(3)Under the limit of transmission power,the introduction of virtual inertia control parameters for doubly-fed wind turbines is studied: the influence of droop control and inertia control with power changes on the oscillation mode,and the suppression of low-frequency oscillations of the regional power grid containing wind power is proposed under different transmission powers.The virtual inertia parameter setting value.This article analogously analyzes the rotor motion equation of the synchronous machine and DFIG after introducing virtual inertia.According to the system angular frequency change rate is inversely proportional to the virtual inertia,the virtual inertia can be adaptively changed according to the rotational speed change and the rate of change within a frequency period.Increase the inertia when the product of frequency change and rate of change is positive to provide dynamic support for the system in real time.Through adaptive inertia control,different virtual inertias are provided for frequency oscillations at different times,which effectively reduces frequency overshoot and suppresses the occurrence of low-frequency oscillations.