| With the increasing demand for electric energy,the pressure of climate change and the continuous advancement of scientific and technological means,the modern power system is gradually developing towards a high proportion of renewable energy and a high proportion of power electronic equipment(that is,"double-high").Compared with the traditional power system,the renewable energy power system represented by wind power has undergone profound changes in the power generation side and power transmission and transformation,resulting in changes in the dynamic characteristics and stability of the system.Subsynchronous oscillation is one of the important issues affecting the safe and stable operation of wind power integrated systems.The subsynchronous oscillation in the traditional power system is usually caused by the torsional vibration of the shafting of the turbine generator,which is limited to a certain area of the system.However,the subsynchronous oscillation of the wind power integrated system has the characteristics of complex generation mechanism,large time-varying range,many components involved and wide range of influence.Therefore,combining the typical subsynchronous oscillation events that have occurred in wind power integrated systems in recent years,it is of great theoretical value and practical significance to study innovative methods for stability analysis,oscillation detection and traceability issues,and to construct a research framework for subsynchronous oscillation analysis.This dissertation takes subsynchronous oscillation in wind power integrated system as the research object,and the major research contents and contributions are as follows:(1)The mathematical modeling and stability analysis of subsynchronous oscillation in wind power integrated systemAn analytical method is proposed for establishing a detailed model of the power system and an oscillatory signal model with state-space equations.On the one hand,the subsynchronous oscillation analysis model is constructed according to the detailed parameters of the power system.Taking into account the characteristics of subsynchronous oscillation,such as many influencing factors,complex fluctuations,and large-scale time-varying characteristics in wind power integrated systems,to ensure that it meets the model accuracy requirements and reproduces power system oscillation events,a method based on small-signal dynamic equations,eigenvalues analysis and stability analysis method of time-domain simulation to study the mechanism of subsynchronous oscillation.The influence of important factors such as AC power grid connection,loading level,and control parameters on the characteristics of subsynchronous oscillation is analyzed,and the correctness of the theory is verified by the electromagnetic transient equation.On the other hand,the oscillatory signal is modeled for electrical signals containing subsynchronous oscillations.The oscillation is studied from the perspective of data,and the waveform signal in the time domain is transformed into a synchrophasor data signal in the frequency domain.Through spectrum analysis,the characteristics of the system’s fundamental frequency and subsynchronous oscillation in the frequency domain are linearly superimposed.This lays the foundation for the research of oscillation detection and identification.(2)The detection method of subsynchronous oscillation in wind power integrated systemAn automatic subsynchronous oscillation detection framework is proposed based on synchrophasor data,multisynchrosqueezing transform,mean-shift cluster algorithm and least squares method.Firstly,the synchrophasor data is processed through multisynchrosqueezing transform to obtain the coefficient expression of the signal in the time-frequency spectrum and the start and end time of the oscillation.Then,the Meanshift algorithm is utilized to cluster the non-zero coefficients to determine the number of modes and corresponding frequencies contained in a subsynchronous oscillation signal.The subsynchronous oscillation signal is reconstructed using the inverse transformation for each mode.Finally,the least squares method is used to process the reconstruction signal to obtain the parameters of each oscillation mode.Taking the IEEE second benchmark model and the modified IEEE first benchmark model as examples,the effectiveness of the proposed method is verified.(3)The parameter identification technique for subsynchronous oscillation in wind power integrated systemThis dissertation presents a method for identifying subsynchronous oscillation parameters based on damped Hanning window function and synchrophasor measurement data.First,according to the subsynchronous oscillation signal model obtained in(1),the expression of the windowed synchrophasor data is obtained,and the relationship between the fundamental frequency and the subsynchronous component in the frequency domain is derived.Then,the damped Hanning window function and the three-point interpolation method are utilized,to identify parameters such as frequency,damping factor,amplitude and phase of the subsynchronous oscillation.By testing the simulation and simulation signals under the conditions of oscillation parameter changes,fundamental frequency dynamic fluctuations,and high or low signal-to-noise ratios,it is verified that the proposed method can effectively suppress spectrum leakage and fence effect,and has high identification accuracy and robustness.(4)The traceability strategy of subsynchronous oscillation source in wind power integrated systemOn the basis of the above research on subsynchronous oscillation,the method of tracing the source of subsynchronous oscillation in wind power integrated systems is further explored.This dissertation proposes two strategies for identifying the oscillation source: Strategy I proposes a subsynchronous oscillation traceability method based on multisynchrosqueezing transform and dissipating energy flow method.Strategy II proposes a source traceability method based on sub/supersynchronous power.The subsynchronous power is extended to SSCI power,and the method of extracting SSCI power and the source identification criterion are proposed.The correctness and feasibility of two strategies are effectively verified through the cases of the wind farm system model in the electromagnetic transient and real-time simulation platform.The proposed two strategies can be utilized to trace sub-synchronous oscillations for the external characteristics of electrical equipment or wind farms respectively,which are not only very simple in method design and not affected by system model parameters,but also due to their low computational complexity and the ability to effectively deal with strong time-varying signals,the oscillation source identification strategies all have excellent engineering application capabilities. |
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