| In order to achieve the grand goal of " peak carbon dioxide emissions " and "carbon neutral",and realize the solemn promise of carbon emission target,the electronization of power sources,network and loads has become the inevitable trend of the development of modern power system,and it is also a significant change in the history of power system development.The electronization of power system meets the demand of clean energy,however causes a series of oscillation problems which threaten the safe and stable operation of power system.Carrying out the research about basic problems of oscillation and technical innovation are the urgent needs to ensure the safe and stable operation of power system.Generally speaking,the existing model-based analysis methods lack of mechanism and universality when applied to the analysis of multi-machine and nonlinear systems.While The data-based analysis method is not affected by the scale of the system and can fully retain the nonlinear characteristics of the system.However,most of the existing methods are based on the understanding of the dynamic process of linear systems and analyze the characteristics of stationary signals.Lack of general understanding of the nonlinear dynamic process of the system leading to the lack of characteristics analysis methods for non-stationary oscillation signals.For the purpose of understanding the system oscillation process from the actual signal characteristics,it is necessary to form a generalized analysis method for non-stationary signal analysis based on the physical process of signal formation.Therefore,based on the physical process of signal formation and aiming at signal characteristic analysis,this paper explores the signal analysis perspective,signal characteristic description method and characteristic analysis method which applicable to non-stationary signal analysis of power system.The main research content of this paper is divided into the following three aspects:(1)The physical meaning of the instantaneous amplitude and frequency modulation and the basic meaning of signal modulation are introduced.The internal voltage of synchronous generator and VSC after disturbance and the response of network are amplitude/frequency varying nonstationary signals.According to the truth,the deficiencies of the harmonic perspective in the analysis of non-stationary signals compared with the amplitude-frequency perspective are summarized from the two aspects of time-frequency resolution and the physical meaning represented by the result.(2)Taking the scene of VSC oscillating after being disturbed at the equilibrium point as the research subject.From the perspective of amplitude and frequency,the basic variation law of the instantaneous amplitude and frequency of internal voltage during the oscillation process is understood.The amplitude-frequency variation characteristics of small perturbations diverging to constant amplitude oscillations are emphatically studied.In this process,new modulation characteristics appear constantly in amplitude and frequency.At the same time,the quantitative analysis of amplitude and frequency modulation characteristics shows that it is impracticable to explain the amplitude and frequency variation laws of the internal voltage signal when the amplitude of oscillation is large in the form of single amplitude and frequency modulation based on the modal analysis.Combined with the idea of multiple amplitude-frequency modulation of state variable in power system,a signal feature description method based on multiple amplitude-frequency modulation is presented.(3)Based on the basic feature of multiple amplitude-frequency modulation signals,a new idea of modulation characteristics extraction is formed,and a method of modulation characteristics quantity extraction is presented.Taking the actual oscillation waveform as the subject,the amplitude-frequency modulation characteristics is analyzed,and the amplitude-frequency modulation characteristics is quantitatively described by the extraction of the amplitude-frequency modulation characteristic quantity,so as to further understand the amplitude-frequency time-varying characteristics of the oscillation signal,and to clarify the cause of the harmonics. |
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