The high proportion of power electronic equipment connected to the grid not only improves the flexibility of power conversion,but also introduces the multi-feature oscillation problem of different forms.However,most of the existing researches focus solely on the macroscopic causes of oscillation,and there are few studies on the accurate extraction of oscillation information and the analytical calculation of oscillation power.Based on a recent field constant amplitude oscillation event,a steady state analysis method for AC circuits under amplitude-frequency modulation excitation based on dq transformation is proposed.First,the waveform characteristics of the medium amplitude oscillation of the event are described,and the shortcomings of the existing methods in extracting the oscillation components directly by discrete Fourier decomposition are explained.The decomposition method of amplitude frequency modulation signal based on dq transform and the measurement method of amplitude frequency modulation signal based on PLL are proposed.Then,the amplitude and frequency excitation signals are calculated to complete the calculation of the active and reactive power of the oscillation,and the analytical expression of the power is given to explain the characteristics of the oscillation waveform.Finally,the proposed method can not only make up for the lack of clear physical meaning of the traditional signal decomposition method,but also clearly reflect the amplitude-frequency nature of oscillation and the influence process of different components on the oscillation power,so as to provide a reference for the analysis and suppression of oscillation.
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