HW-DFT-Based Measurement Method of Frequency-Coupling Characteristics Considering Fundamental Frequency Deviation for Stability Analysis

Impedance measurement is an effective method to obtain the impedance characteristic of the renewable power generator. Discrete Fourier transformation (DFT) is commonly used to extract measurement signals. However, when there is a slight fundamental frequency deviation (FFD), the frequency resolution of DFT may be insufficient due to spectral leakage (SL). Under this circumstance, the measurement signals will be overlapped with the fake spectra caused by the SL and unable to be extracted precisely. Besides, when the frequency-coupling characteristic exists, FFD will also lead to a change in coupling frequencies. Thus, SL will also happen at the coupling frequencies, making it more difficult to extract measurement signals. Targeting this issue, this article analyzes the mechanism of SL and grasps the characteristics of fake spectra caused by SL. Accordingly, a Hann-window-based method is proposed to accurately extract the measurement signals during FFD. The superiority of the proposed method is none of the requirements to extend the original measurement time. Finally, the experiments based on control-hardware-in-loop are carried out to verify the effectiveness of the proposed method.